# Energycount — full text (tools, reference, guides & news) > UK energy & sustainability consultants (est. 2006, Poole, Dorset) and the free "Monkey" building-compliance calculators. Index: https://energycount.co.uk/llms.txt · Reference figures: https://energycount.co.uk/reference/ · Datasets: https://energycount.co.uk/data/ · Tools: https://energycount.co.uk/tools/ · Pricing: https://energycount.co.uk/pricing/ ## TOOLS & PRICING --- # U-Monkey — the free U-value calculator URL: https://energycount.co.uk/tools/u-value-calculator/ A free, browser-based U-value calculator with no sign-up and no account. Calculates to BS EN ISO 6946 using BR 443 conventions, with ISO 13370 for ground floors, and shows the U-value live as layers are added or changed. Elements covered: external, party and internal walls; roofs with insulation at rafter or at ceiling; flat roofs; exposed floors; solid ground floors (ISO 13370); and suspended ground floors. What it gives you free: the live U-value, a self-drawing cross-section of the build-up, pass/fail against the Part L 2021 limiting value, the notional dwelling value and the Future Homes Standard level, a 300+ item neutral database of real UK materials and products (no manufacturer favourites), and a Building Control-ready PDF report with the full layer breakdown, method references and a unique report ID. The PDF is free — there is no paywall on a U-value report. It also includes an interstitial condensation-risk screening to BS 5250 / BS EN ISO 13788 (the monthly Glaser method) built into the same build-up, so a wall that passes on U-value but fails on condensation shows up in one place. This is a screening to ISO 13788; it is NOT full or transient hygrothermal modelling to BS EN 15026, and Energycount does not offer that. Paid extra: U-Monkey Pro (£19/month +VAT) adds project, client and revision references and your practice branding to the report. A one-off branded single report is £7 +VAT. A standalone paid condensation report is £25 +VAT (£10 on Monkey Pro, included on Pro Unlimited). Related: /tools/u-value-calculator/how-to-use/ (full tutorial), /tools/u-value-calculator/condensation-risk-calculator/, /tools/u-value-calculator/what-u-value-do-i-need/, and /tools/u-value-calculator/demo/ (28-second silent screencast with a written second-by-second description). --- # ΨMonkey — the free psi value calculator URL: https://energycount.co.uk/tools/psi-calculator/ A free 2D thermal-bridge (psi value) calculator running in the browser. Numerical solution to BS EN ISO 10211 for linear thermal transmittance (Ψ) and the internal surface temperature factor f_Rsi, for use in SAP 10 and the Home Energy Model. 38 ready-made standard SAP junctions are built in: the E-series E1–E25 (external wall junctions), the party-wall P-series P1–P8, and the roof-window R-series R1–R4. A build-up assistant turns a layer list into a modelled junction on the grid, and Ψ and f_Rsi update live as thicknesses and materials change. You can also draw a junction by hand on the modelling canvas and set surface and edge boundary conditions. Accuracy evidence: the solver is validated against the BS EN ISO 10211 test reference cases and the results are published at /tools/psi-calculator/validation/ — the strongest trust asset on the site. Using calculated Ψ-values instead of SAP default y-values is usually the cheapest route to a Part L pass, because the defaults are deliberately punitive. Free: unlimited modelling, unlimited solving, Ψ and f_Rsi on screen. Paid: a Building Control-ready PDF report per junction, £35 +VAT (£15 on Monkey Pro, included on Pro Unlimited). No subscription is required — you can pay for a single junction. Related: /tools/psi-calculator/validation/, /tools/psi-calculator/guide/ (user guide), /tools/psi-calculator/free-alternative-to-autopsi/, /tools/psi-calculator/free-psi-calculator-no-subscription/, and /tools/psi-calculator/demo/ (22-second silent screencast with a written second-by-second description). --- # WaterMonkey — the free Part G water calculator URL: https://energycount.co.uk/tools/part-g-water-calculator/ A free water efficiency calculator for Part G of the Building Regulations (Requirement G2 / regulation 36), running in the browser with no sign-up. It implements the official water efficiency calculation methodology for new dwellings and shows a live PASS/FAIL against either the 125 litres per person per day Building Regulations standard or the tighter 110 l/p/d optional requirement imposed by many planning conditions. Inputs are the fittings schedule: WC flush volumes (single, dual or multiple), tap flow rates, bath capacity to overflow, shower flow rate, kitchen and utility sink taps, washing machine litres per kg dry load, dishwasher litres per place setting, plus optional waste disposal unit and water softener, and greywater recycling or rainwater harvesting where installed. Quick presets fill an entire dwelling type in one tap — typical 125 l/p/d, tight 110 l/p/d, very tight 90 l/p/d, or AD G default appliances — and the total recalculates instantly. Free: the full methodology and the live result, for as many dwelling types as you like. Paid: a Building Control-ready PDF report, £25 +VAT for the first dwelling type plus £15 +VAT for each additional type in the same report — so a scheme with several house types is one fee, not several. Note on London: a 105 l/p/d planning condition that excludes external water use is the same target as 110 l/p/d including it. Related: /tools/part-g-water-calculator/110-litres/, /tools/part-g-water-calculator/water-efficiency-calculator-spreadsheet/, /tools/part-g-water-calculator/shower-flow-rate/, and /tools/part-g-water-calculator/demo/ (28-second silent screencast with a written second-by-second description). --- # SoakMonkey — the BRE 365 soakaway calculator URL: https://energycount.co.uk/tools/soakaway-calculator/ A free soakaway sizing calculator working to BRE Digest 365 (Soakaway Design), the method Building Control and most LLFAs expect. Runs in the browser, no sign-up. It takes the percolation test results (trial pit length, width and effective storage depth, plus the time for the water level to fall from 75% to 25% effective depth on each of three fills), computes the infiltration rate f for each test and adopts the lowest for design, exactly as BRE 365 requires. It then runs the storm duration sweep against FSR rainfall data — impermeable area drained, rainfall ratio r, M5-60 rainfall, return period and a climate change uplift on rainfall — and reports the required storage volume, the half-empty (half-drain) time, and a DESIGN OK / not OK verdict. Four construction types are supported: filled pit, modular crate, concrete ring and trench, each dimensioned for the storage required. Free: the whole calculation and the sizing on screen, unlimited. Paid: a Building Control-ready PDF report, £25 +VAT. Related: /tools/soakaway-calculator/what-size-soakaway-do-i-need/, /tools/soakaway-calculator/percolation-test/, /tools/soakaway-calculator/bre-digest-365/, /tools/soakaway-calculator/soakaway-for-an-extension/, and /tools/soakaway-calculator/demo/ (17-second silent screencast with a written second-by-second description). --- # NutrientMonkey — the nutrient neutrality calculator URL: https://energycount.co.uk/tools/nutrient-neutrality-calculator/ A free nutrient budget calculator for residential development in nutrient neutrality catchments, implementing Natural England's nutrient budget methodology in the browser. All 27 Natural England catchments are built in, for nitrogen and for phosphorus, with NE's published default concentrations and the ×1.2 precautionary buffer. It builds the budget the way the planning application needs it: waste water from the new dwellings (number of dwellings, occupancy, water efficiency standard, drainage route and the receiving works' current and post-2030 total nitrogen permit), current land use, future land use, and any SuDS removal — then reports the pre-2030 and post-2030 budgets and the permanent credit requirement in kg per year, with a plain statement of how many credits are needed and how they can be secured (permanent credits, or temporary credits to 2030 plus permanent credits for the enduring baseline). Land-use export coefficients are catchment-, soil-, rainfall- and NVZ-specific; the tool says so on the page and asks you to confirm against the official NE calculator for your site. Free: the whole calculation on screen. Paid: a planning-ready PDF assessment, £79 +VAT. Related: catchment pages under /tools/nutrient-neutrality-calculator/, and /tools/nutrient-neutrality-calculator/demo/ (23-second silent screencast with a written second-by-second description). --- # Pricing — every calculator free, pay per report, or Monkey Pro URL: https://energycount.co.uk/pricing/ Every Energycount calculator is free to use in full, with no sign-up and no account. You pay only when you want a Building Control-ready PDF report, or for a subscription that brands your reports and cuts the report price. Pay-per-report list prices (all +VAT): - U-value report (U-Monkey) — free, on every tier. - Condensation risk report — £25 (Monkey Pro £10; included on Pro Unlimited). - Thermal bridge / psi report (ΨMonkey) — £35 per junction (Monkey Pro £15; included on Pro Unlimited). - Part G water calculation report (WaterMonkey) — £25, plus £15 for each additional dwelling type in the same report. Same price on every tier. - Soakaway report (SoakMonkey) — £25. Same price on every tier. - Nutrient neutrality assessment (NutrientMonkey) — £79. Same price on every tier. - Branding on a single U-value report without a subscription — £7, a one-off credit against your account. Subscriptions (+VAT): - Monkey Pro — £19/month or £190/year (two months free). Your logo and practice details on every report from every tool, plus member rates: thermal bridge reports £15 instead of £35, condensation reports £10 instead of £25. - Monkey Pro Unlimited — £49/month or £490/year (two months free). Everything in Monkey Pro, with thermal bridge and condensation reports included outright, however many you produce. Part G, soakaway and nutrient reports are charged at list price on every tier; only the branding changes. Two thermal bridge reports in a month and Pro Unlimited is already cheaper than Monkey Pro. For comparison, AutoPSI's published pricing (June 2026) was £59/month or £649/year ex VAT for a single Professional thermal-bridging licence; Pro Unlimited is £49/month and covers every Energycount tool, and you can skip it entirely and pay £35 for the one junction you need. Reports carry a unique report ID that can be checked at /verify/. ## REFERENCE — THE COMPLIANCE FIGURES ON ONE DATED PAGE --- # Building regulations reference URL: https://energycount.co.uk/reference/ Updated: 2026-09-04 The figures UK energy assessors look up every week, each with its source document and the date it was last checked. England unless stated. Cite as: Energycount, Building regulations reference, energycount.co.uk/reference/, reviewed 4 September 2026. ## Part L U-values (W/m²K) Source: Approved Document L Volume 1, 2021 edition incorporating 2023 amendments — Table 1.1 (notional dwelling), Table 4.1 (limiting values, new dwellings), Table 4.2 (new elements in existing dwellings), Table 4.3 (retained elements); Approved Document L 2026 for the Future Homes Standard notional dwelling. Checked 4 September 2026. | Element | Notional — Part L 2021 | Notional — FHS from 24 March 2027 (SAP 10.3 and HEM) | Limiting, new dwelling (unchanged in 2027) | New element in an existing dwelling | Retained element — upgrade if worse than → to | | --- | --- | --- | --- | --- | --- | | External wall | 0.18 | 0.18 | 0.26 | 0.18 | 0.70 → 0.55 (cavity fill) / 0.30 (internal or external insulation) | | Floor | 0.13 | 0.13 | 0.18 | 0.18 | 0.70 → 0.25 | | Roof | 0.11 | 0.11 | 0.16 | 0.15 | 0.35 → 0.16 | | Party wall | 0 | 0 | 0.20 | — | — | | Windows | 1.2 | 1.2 | 1.6 | 1.4 (or WER band B) | — | | Doors | 1.0 | 1.0 | 1.6 | 1.4 (or DSER band B/C) | — | | Rooflights | 1.7 | 1.7 | 2.2 | 2.2 | — | | Air permeability, m³/(h·m²) at 50 Pa | 5.0 | 4.0 | 8.0 | — | — | The notional dwelling sets the target a design is measured against; the limiting values are the worst any element may be. The Future Homes Standard notional keeps the 2021 fabric and tightens air permeability to 4.0; the Home Energy Model version of it differs only in how the notional heat pump is modelled, not in fabric. Explained at /guides/u-values/ and /guides/future-homes-standard/; calculate a build-up free at /tools/u-value-calculator/; extensions: the 25% glazing checker at /services/sap-calculations/extensions/. ## Part L editions and transitional dates Source: The Building Regulations etc. (Amendment) (England) Regulations 2021 and 2026; Future Homes and Buildings Standards Building Circular 01/2026; Welsh and Scottish government publications. Checked 4 September 2026. | Date | What | | --- | --- | | 15 June 2022 | Approved Document L 2021 in force (England); every new dwelling air-tested individually from this date | | 15 June 2023 | Part L 2013 transitional window closed — the 2013 edition is fully revoked | | 23 November 2022 | Wales: Approved Document L 2022 edition in force | | 1 February 2023 | Scotland: revised Section 6 (Energy) standards in force | | 24 March 2026 | SAP 10.3 becomes the sole approved SAP methodology; Approved Document L 2026 published | | 24 March 2027 | Approved Document L 2026 (Future Homes Standard) in force for non-higher-risk work; last day to give a building notice, initial notice or full plans under Part L 2021 | | 24 September 2027 | Future Homes Standard in force for higher-risk buildings; a valid Gateway 2 application before this date completes under Part L 2021 | | 24 March 2028 | Transitional deadline: each building notified before 24 March 2027 must have commenced — foundations and the ground-floor structure complete — to keep Part L 2021 | Transitional protection is per building, not per site. Which edition a scheme falls under: the checker at /guides/building-regulations-part-l/#part-l-checker. Explained at /guides/building-regulations-part-l/ and /guides/future-homes-standard/. ## SAP: the carbon and primary energy factors, and the notional dwelling Source: SAP 10.3 specification (12-06-2026 version), Table 12 and Appendix R Table R1 — SAP 10.3 has been the approved methodology for new dwellings in England since 24 March 2026 (Notice of Approval); SAP 10.2 Table 12 and BRE technical paper S10TP-15 for the earlier factors; Approved Document L Volume 1 2021, Table 1.1 for the Part L 2021 notional dwelling. Checked 4 September 2026. | Item | Value | Note | | --- | --- | --- | | Grid electricity — CO₂ factor | 0.086 kgCO₂e/kWh (SAP 10.3) | Forward-looking figure, the same for every tariff; the annual average is used directly (SAP 10.3 keeps monthly factors for comparison only). 0.136 in SAP 10.2, 0.233 in SAP 10.0, 0.519 in SAP 2012 | | Mains gas — CO₂ factor | 0.214 kgCO₂e/kWh (SAP 10.3) | 0.210 in SAP 10.2; 0.216 in SAP 2012. Electricity is now well below gas | | Grid electricity — primary energy factor | 1.969 (SAP 10.3) | Up from 1.501 in SAP 10.2 (3.07 in SAP 2012); feeds the DPER ≤ TPER test, the headline test | | Mains gas — primary energy factor | 1.12 (SAP 10.3) | 1.130 in SAP 10.2; 1.22 in SAP 2012 | | Notional dwelling PV — Part L 2021 | kWp = 40% of ground-floor area (unheated spaces included) ÷ 6.5 | Roughly 4 kWp on an average house. Flats: 40% of the flat’s floor area ÷ (6.5 × storeys in the block) | | Notional dwelling PV — Future Homes Standard | kWp = 40% of ground-floor area ÷ 4.5 (flats: ÷ storeys ÷ 4.5) | SAP 10.3 Appendix R; PV is also a functional requirement (L3) from 24 March 2027 | | Notional dwelling heating | 2021: gas boiler, 89.5% efficient, 55 °C flow temperature | FHS: heat pump at a SCOP of 2.5, with dMEV ventilation | | Notional dwelling air permeability | 5.0 m³/(h·m²) | 4.0 under the FHS notional (SAP 10.3) | | Notional dwelling WWHR | Assumed on every shower | Waste water heat recovery — leave it out and the target gets harder (FHS: not assumed in single-storey dwellings) | | Fixed lighting efficacy | Minimum 75 lumens per circuit-watt | Notional dwelling assumes 80 (2021) and 120 (FHS) | SAP 10.3 replaced SAP 10.2 as the approved methodology on 24 March 2026 with revised carbon and primary energy factors — the electricity figures are the ones that move results. The four tests a new dwelling passes at once — DPER ≤ TPER, DER ≤ TER, DFEE ≤ TFEE and the limiting values — are explained at /guides/building-regulations-part-l/, /guides/der-ter/ and /guides/fabric-energy-efficiency/. SAP 10 changes: /guides/sap-10-whats-new/. ## Air tightness (Part L) Source: Approved Document L Volume 1 2021, Regulation 43 and Table 4.1; Approved Document L 2026; Volume 2 for non-domestic. Checked 4 September 2026. | Item | Value | | --- | --- | | Measured quantity | q50 — air permeability, m³ of air per hour per m² of envelope at 50 Pa. Not the same as n50 (air changes per hour, used by Passivhaus); there is no valid conversion between them | | Limiting value (worst permitted) | 8.0 m³/(h·m²) — dwellings and non-domestic buildings alike | | Notional dwelling — Part L 2021 | 5.0 m³/(h·m²) | | Notional dwelling — Future Homes Standard (from 24 March 2027) | 4.0 m³/(h·m²) | | Who is tested | Every new dwelling, individually, since 15 June 2022 — sample testing has gone; Wales the same under its 2022 edition | | Who may test | A tester registered with a scheme the regulation recognises — ATTMA or Elmhurst (Regulation 43); the result goes into the as-built SAP | If the design SAP assumed 5 and the test comes back at 7, the as-built SAP uses 7 and the shortfall must be made up elsewhere. Service and pre-test checklist: /services/air-tightness-testing/. ## Part O overheating — the simplified method tables Source: Approved Document O, 2021 edition (in force 15 June 2022): Tables 1.1–1.4, paragraphs 1.3–1.9 and 3.2–3.3. Glazing is the transparent area, frames excluded; limits are read for the façade with the largest glazed area. High-risk locations are the London postcode districts in Appendix C; everywhere else is moderate risk. CIBSE TM59 (2017) for the dynamic-modelling criteria and weather file. Checked 4 September 2026. ### Maximum glazing area — cross-ventilated (Table 1.1) | Largest glazed façade | High risk: % of floor area | High risk: most glazed room | Moderate risk: % of floor area | Moderate risk: most glazed room | | --- | --- | --- | --- | --- | | North | 15% | 37% | 18% | 37% | | East | 18% | 37% | 18% | 37% | | South | 15% | 22% | 15% | 30% | | West | 18% | 37% | 11% | 22% | ### Maximum glazing area — not cross-ventilated (Table 1.2) | Largest glazed façade | High risk: % of floor area | High risk: most glazed room | Moderate risk: % of floor area | Moderate risk: most glazed room | | --- | --- | --- | --- | --- | | North | 15% | 26% | 18% | 26% | | East | 11% | 18% | 18% | 26% | | South | 11% | 11% | 15% | 15% | | West | 11% | 18% | 11% | 11% | ### Minimum free area for removing heat (Tables 1.3 and 1.4) | Situation | High risk | Moderate risk | | --- | --- | --- | | Cross-ventilated — whole dwelling | greater of 6% of floor area or 70% of glazing area | greater of 9% of floor area or 55% of glazing area | | Cross-ventilated — each bedroom | 13% of the room's floor area | 4% of the room's floor area | | Not cross-ventilated — whole dwelling | greater of 10% of floor area or 95% of glazing area | greater of 12% of floor area or 80% of glazing area | | Not cross-ventilated — each bedroom | 13% of the room's floor area | 4% of the room's floor area | ### The other Part O numbers | Item | Value | | --- | --- | | Shading in high-risk locations | Glazing facing between north-east and north-west via south: external shutters, g-value ≤ 0.4 with light transmittance ≥ 0.7, or (south only) an overhang cutting the sun off at 50° altitude | | Night-time noise that defeats open windows | 40 dB LAeq averaged 11pm–7am, or 55 dB LAFmax more than 10 times a night, in a bedroom with the windows open → dynamic modelling | | TM59 (2017) pass criteria | Living rooms, kitchens, bedrooms: ≤ 3% of occupied hours May–September more than 1 K over the adaptive threshold; bedrooms 10pm–7am: ≤ 1% of annual hours (32 h) above 26 °C | | Weather file (TM59) | CIBSE DSY1, 2020s, high emissions, 50th percentile | | Applies to | New residential buildings only — not extensions, not material change of use. Wales: own AD O from 23 November 2022. Scotland: Standard 3.28 from 1 December 2022 | Explained at /guides/building-regulations-part-o/; assessments (simplified method or TM59) at /services/part-o-overheating/; TM59:2026 changes at /news/cibse-tm59-2026-overheating-update/. ## Part G water efficiency Source: Building Regulation 36 and Approved Document G; The Water Efficiency Calculator for New Dwellings (DCLG, 2009), Table 1 — the same constants WaterMonkey uses. Checked 4 September 2026. | Standard | Litres per person per day | When | | --- | --- | --- | | Regulation 36(2) — every new dwelling | 125 | The default for Building Control | | Optional requirement (Regulation 36(3)) | 110 | Where the local plan applies it — most water-stressed areas; the August 2026 NPPF keeps this in place | | London Plan | 105 excluding external use | The same target as 110 with the 5 l/p/d external allowance | | Proposed (Defra consultation, closed 16 December 2025) | 105, with 100 as the optional standard | Government response awaited; implementation intended during 2026 with a six-month transition | ### Table 1 use factors | Fitting | Unit | Use factor | Fixed use (l/p/d) | Effect of one unit on the final figure | | --- | --- | --- | --- | --- | | Shower (bath also present) | Flow rate, litres/minute | 4.37 | 0.00 | 3.98 l/p/d | | Shower only (no bath) | Flow rate, litres/minute | 5.60 | 0.00 | 5.10 l/p/d | | WC, dual flush — full flush | Full flush volume, litres | 1.46 | 0.00 | 1.33 l/p/d | | WC, dual flush — part flush | Part flush volume, litres | 2.96 | 0.00 | 2.69 l/p/d | | WC, single flush | Flush volume, litres | 4.42 | 0.00 | 4.02 l/p/d | | Taps, excluding kitchen and utility | Flow rate, litres/minute | 1.58 | 1.58 | 1.44 l/p/d | | Kitchen and utility sink taps | Flow rate, litres/minute | 0.44 | 10.36 | 0.40 l/p/d | | Bath (shower also present) | Capacity to overflow, litres | 0.11 | 0.00 | 0.10 l/p/d | | Bath only (no shower) | Capacity to overflow, litres | 0.50 | 0.00 | 0.46 l/p/d | | Washing machine | Litres per kg of dry load | 2.1 | 0.00 | 1.91 l/p/d | | Dishwasher | Litres per place setting | 3.6 | 0.00 | 3.28 l/p/d | | Waste disposal unit, if fitted | Present or not | 1 | 3.08 | 0.91 l/p/d | Consumption = Σ(capacity × use factor + fixed use) × 0.91 normalisation, plus 5 l/p/d external use. Consumption = Σ(capacity × use factor + fixed use) × 0.91 normalisation, plus 5 l/p/d external use. Why 105-excluding-external equals 110: /guides/110-litres-water-planning-condition/. Machine-readable factors: /data/. Calculate at /tools/part-g-water-calculator/; explained at /guides/water-calculation-building-control/ and /guides/125-litres-per-person-per-day/. ## Part E sound insulation Source: Approved Document E, Table 0.1a (dwellings) and 0.1b (rooms for residential purposes); Regulation 41 pre-completion testing. Checked 4 September 2026. | Separating element | Airborne, DnT,w + Ctr (minimum) | Impact, L'nT,w (maximum) | | --- | --- | --- | | New-build houses and flats — walls | 45 dB | — | | New-build houses and flats — floors | 45 dB | 62 dB | | Houses and flats formed by material change of use — walls | 43 dB | — | | Houses and flats formed by material change of use — floors | 43 dB | 64 dB | | Rooms for residential purposes (student halls, hotels, hostels), purpose-built — walls | 43 dB | — | | Rooms for residential purposes, purpose-built — floors | 45 dB | 62 dB | | Rooms for residential purposes, change of use — walls | 43 dB | — | | Rooms for residential purposes, change of use — floors | 43 dB | 64 dB | Higher is better for airborne, lower for impact. The conversion values are 2 dB easier because a retained structure cannot always be brought to new-build performance. Pre-completion testing is the default route; registered Robust Details are the alternative for new-build houses and flats. Service: /services/sound-testing/. ## Soakaways — BRE Digest 365 in numbers Source: BRE Digest 365 Soakaway design (2016 edition); Approved Document H. Checked 4 September 2026. | Item | Value | | --- | --- | | Infiltration test | Trial pit 0.3–1 m wide and 1–3 m long, dug to the depth the soakaway will reach; fill to ≥ 75% effective depth; time the fall 75% → 25%; three fills on the same or consecutive days; design on the slowest | | Infiltration rate | f = V(75–25) ÷ (a(p50) × t(75–25)), in m/s — below about 1×10⁻⁶ m/s (heavy clay) a soakaway is rarely practical | | Design storm | 1-in-10-year return period, checked across every duration; the critical duration governs | | Climate-change allowance | An uplift on design rainfall; 40% is what most local authorities ask for on new drainage | | Storage available | Volume × void ratio — 30–40% for a gravel-filled pit, 90–95% for crates | | Half-drain check | Full to half-full within 24 hours: t(s50) = 0.5 S ÷ (a(s50) × f) | | Separation | At least 5 m from any building (Approved Document H) | Not the septic-tank drainage-field test: that one uses a 300 mm square hole and gives a Vp in seconds per millimetre (a drainage field needs Vp 12–100) — the difference is explained at /tools/soakaway-calculator/percolation-test/. Calculate at /tools/soakaway-calculator/; the method at /tools/soakaway-calculator/bre-digest-365/. ## Junction Ψ-values (W/m·K) — calculated, not default Source: ΨMonkey’s own BS EN ISO 10211 solves of the standard SAP junction templates against named wall build-ups; solver validated against the ISO 10211 test reference case. Library generated 2 September 2026. Ψ in W/(m·K), with the temperature factor f_Rsi in brackets. A negative Ψ on a non-inverted junction means the template’s default detail does not suit that wall — model your own rather than use the figure. The full 38-template library is at https://energycount.co.uk/tools/psi-calculator/psi-values/ and every figure can be reproduced free at https://energycount.co.uk/tools/psi-calculator/app/?junction=&wall=. Walls: masonry-full = Cavity masonry — full fill (accredited default) (U 0.18); masonry-partial = Cavity masonry — partial fill + 50 mm clear cavity (U 0.28); tf-brick = Timber frame — brick clad, 140 mm studs (15% bridged) (U 0.27); tf-brick-sv = Timber frame — brick clad, 140 studs + service void (U 0.26); tf-pir-sheath = Timber frame — 140 studs + 50 mm PIR over the sheathing (U 0.16); tf-render = Timber frame — render / rainscreen, 140 mm studs (U 0.28); tf-twin = Closed panel / twin stud — 300 mm cellulose (8% bridged) (U 0.11); clt-ewi = CLT + external insulation — 100 CLT, 160 woodfibre (U 0.18). | Junction | masonry-full | masonry-partial | tf-brick | tf-brick-sv | tf-pir-sheath | tf-render | tf-twin | clt-ewi | | --- | --- | --- | --- | --- | --- | --- | --- | --- | | E1 Lintel — steel (window head) | 0.223 (0.819) | 0.198 (0.819) | 0.162 (0.819) | 0.185 (0.819) | 0.210 (0.820) | 0.164 (0.819) | 0.218 (0.821) | 0.224 (0.820) | | E2 Lintel — insulated, no base plate (window head) | 0.197 (0.809) | 0.171 (0.809) | 0.117 (0.839) | 0.241 (0.806) | 0.307 (0.806) | 0.119 (0.835) | 0.446 (0.806) | 0.321 (0.806) | | E3 Cill (window sill) | 0.047 (0.751) | 0.037 (0.747) | 0.018 (0.817) | 0.033 (0.737) | 0.043 (0.738) | 0.018 (0.817) | 0.055 (0.734) | 0.039 (0.741) | | E4 Jamb (window reveal) | 0.005 (0.850) | −0.000 (0.848) | 0.026 (0.828) | 0.026 (0.827) | 0.030 (0.828) | 0.026 (0.827) | 0.039 (0.826) | 0.028 (0.830) | | E5 Ground floor (suspended beam & block) | 0.071 (0.862) | 0.108 (0.832) | 0.055 (0.822) | 0.042 (0.893) | 0.051 (0.899) | 0.056 (0.818) | 0.037 (0.925) | 0.059 (0.871) | | E5s Ground floor (solid ground-bearing slab) | 0.094 (0.872) | 0.132 (0.842) | 0.081 (0.826) | 0.077 (0.893) | 0.087 (0.897) | 0.082 (0.822) | 0.075 (0.921) | 0.098 (0.863) | | E6 Intermediate floor (within dwelling) | 0.008 (0.973) | 0.078 (0.947) | 0.249 (0.862) | 0.006 (0.966) | 0.021 (0.977) | 0.278 (0.851) | 0.001 (0.986) | 0.005 (0.977) | | E10 Eaves (insulation at ceiling level) | 0.035 (0.944) | 0.050 (0.934) | 0.030 (0.922) | 0.028 (0.936) | 0.037 (0.942) | 0.030 (0.921) | 0.031 (0.946) | 0.039 (0.942) | | E11 Eaves (insulation at rafter level) | 0.056 (0.957) | 0.022 (0.954) | 0.025 (0.940) | 0.021 (0.955) | 0.027 (0.969) | 0.035 (0.937) | 0.032 (0.965) | 0.027 (0.963) | | E16 Corner (normal) | 0.037 (0.947) | −0.011 (0.930) | 0.039 (0.926) | 0.025 (0.929) | 0.014 (0.950) | 0.040 (0.925) | 0.031 (0.960) | 0.046 (0.943) | | E18 Party wall / external wall | −0.001 (0.973) | 0.046 (0.951) | −0.007 (0.959) | −0.003 (0.960) | 0.017 (0.973) | −0.007 (0.958) | −0.001 (0.983) | 0.000 (0.972) | ## Nutrient neutrality — the 27 Natural England catchments Source: Natural England’s nutrient neutrality advice and catchment calculators (NECR459 methodology, 20% precautionary buffer). Checked 4 September 2026. | Catchment | Designated site | Nutrient | Region | Page | | --- | --- | --- | --- | --- | | Poole Harbour | Poole Harbour SPA / Ramsar | Nitrogen | Dorset | https://energycount.co.uk/tools/nutrient-neutrality-calculator/poole-harbour/ | | Solent | Solent (incl. Chichester & Portsmouth Harbours) | Nitrogen | Hampshire, West Sussex & Isle of Wight | https://energycount.co.uk/tools/nutrient-neutrality-calculator/solent/ | | Tees (Teesmouth) | Teesmouth & Cleveland Coast SPA / Ramsar | Nitrogen | Teesside, Durham & North Yorkshire | https://energycount.co.uk/tools/nutrient-neutrality-calculator/tees/ | | Lindisfarne | Lindisfarne SPA / Ramsar | Nitrogen | Northumberland | https://energycount.co.uk/tools/nutrient-neutrality-calculator/lindisfarne/ | | Stodmarsh | Stodmarsh SAC / SPA / Ramsar | Nitrogen and phosphorus | Kent | https://energycount.co.uk/tools/nutrient-neutrality-calculator/stodmarsh/ | | The Broads | The Broads SAC | Nitrogen and phosphorus | Norfolk & Suffolk | https://energycount.co.uk/tools/nutrient-neutrality-calculator/the-broads/ | | River Wensum | River Wensum SAC | Nitrogen and phosphorus | Norfolk | https://energycount.co.uk/tools/nutrient-neutrality-calculator/river-wensum/ | | Chesil & the Fleet | Chesil & the Fleet SAC / SPA / Ramsar | Nitrogen and phosphorus | Dorset | https://energycount.co.uk/tools/nutrient-neutrality-calculator/chesil-and-the-fleet/ | | Hornsea Mere | Hornsea Mere SPA | Nitrogen and phosphorus | East Yorkshire | https://energycount.co.uk/tools/nutrient-neutrality-calculator/hornsea-mere/ | | Oak Mere | Oak Mere SAC | Nitrogen and phosphorus | Cheshire | https://energycount.co.uk/tools/nutrient-neutrality-calculator/oak-mere/ | | Rostherne Mere | Rostherne Mere Ramsar | Nitrogen and phosphorus | Cheshire | https://energycount.co.uk/tools/nutrient-neutrality-calculator/rostherne-mere/ | | West Midlands Mosses | West Midlands Mosses SAC | Nitrogen and phosphorus | Shropshire, Staffordshire & Cheshire | https://energycount.co.uk/tools/nutrient-neutrality-calculator/west-midlands-mosses/ | | River Clun | River Clun SAC | Nitrogen and phosphorus | Shropshire | https://energycount.co.uk/tools/nutrient-neutrality-calculator/river-clun/ | | River Avon (Christchurch) | River Avon SAC (→ Christchurch Harbour) | Phosphorus | Wiltshire, Hampshire & Dorset | https://energycount.co.uk/tools/nutrient-neutrality-calculator/river-avon/ | | Somerset Levels & Moors | Somerset Levels & Moors SPA / Ramsar | Phosphorus | Somerset | https://energycount.co.uk/tools/nutrient-neutrality-calculator/somerset-levels/ | | River Itchen | River Itchen SAC | Phosphorus | Hampshire | https://energycount.co.uk/tools/nutrient-neutrality-calculator/river-itchen/ | | River Axe | River Axe SAC | Phosphorus | Somerset, Devon & Dorset | https://energycount.co.uk/tools/nutrient-neutrality-calculator/river-axe/ | | River Camel | River Camel SAC | Phosphorus | Cornwall | https://energycount.co.uk/tools/nutrient-neutrality-calculator/river-camel/ | | Derwent & Bassenthwaite | River Derwent & Bassenthwaite Lake SAC | Phosphorus | Cumbria | https://energycount.co.uk/tools/nutrient-neutrality-calculator/river-derwent-bassenthwaite/ | | River Eden | River Eden SAC | Phosphorus | Cumbria | https://energycount.co.uk/tools/nutrient-neutrality-calculator/river-eden/ | | River Kent | River Kent SAC | Phosphorus | Cumbria | https://energycount.co.uk/tools/nutrient-neutrality-calculator/river-kent/ | | River Lambourn | River Lambourn SAC | Phosphorus | Berkshire | https://energycount.co.uk/tools/nutrient-neutrality-calculator/river-lambourn/ | | River Lugg | River Lugg SAC (River Wye system) | Phosphorus | Herefordshire | https://energycount.co.uk/tools/nutrient-neutrality-calculator/river-lugg/ | | River Mease | River Mease SAC | Phosphorus | Leicestershire, Derbyshire & Staffordshire | https://energycount.co.uk/tools/nutrient-neutrality-calculator/river-mease/ | | Esthwaite Water | Esthwaite Water Ramsar | Phosphorus | Cumbria | https://energycount.co.uk/tools/nutrient-neutrality-calculator/esthwaite-water/ | | Peak District Dales | Peak District Dales SAC | Phosphorus | Derbyshire & Staffordshire | https://energycount.co.uk/tools/nutrient-neutrality-calculator/peak-district-dales/ | | Roman Walls Loughs | Roman Walls Loughs SAC | Phosphorus | Northumberland | https://energycount.co.uk/tools/nutrient-neutrality-calculator/roman-walls-loughs/ | Calculate a nutrient budget free at https://energycount.co.uk/tools/nutrient-neutrality-calculator/ (planning-ready PDF £79 +VAT). Machine-readable list: https://energycount.co.uk/data/. ## Regs calendar Source: the instruments, circulars and consultations linked in each row. Checked 4 September 2026. | Date | What | More | | --- | --- | --- | | 24 March 2026 | SAP 10.3 becomes the sole approved SAP methodology; Approved Documents L, F and the 2026 suite published | https://energycount.co.uk/guides/future-homes-standard/ | | July 2026 | CIBSE TM59:2026 published — Approved Document O still cites the 2017 edition | https://energycount.co.uk/news/cibse-tm59-2026-overheating-update/ | | 6 August 2026 | RdSAP Conventions v12.2 apply | https://energycount.co.uk/news/rdsap-conventions-v12-2-6-august-2026/ | | 6 August 2026 | Biodiversity Net Gain: 0.2 ha small-site exemption and other changes, for applications from this date | https://energycount.co.uk/news/biodiversity-net-gain-exemptions-6-august-2026/ | | 27 August 2026 | GPDO Amendment Order 2026 — rewritten permitted development rights for domestic and plug-in solar | https://energycount.co.uk/news/gpdo-solar-permitted-development-27-august-2026/ | | 30 September 2026 | Second staircase requirement (Approved Document B 2026 amendments) in force for residential buildings 18 m and above | https://www.gov.uk/government/publications/fire-safety-approved-document-b | | 1 October 2026 | Building Safety Levy starts — collected via Building Control, completion certificate withheld until paid | https://energycount.co.uk/news/building-safety-levy-1-october-2026/ | | 5 October 2026 | Consultation closes: planning powers for mayors in England | https://energycount.co.uk/news/mayoral-planning-powers-consultation-october-2026/ | | 16 October 2026 | Consultation closes: Scotland’s Passivhaus-equivalent standard, stage 2 (implementation now autumn 2029) | https://energycount.co.uk/news/scotland-passivhaus-equivalent-stage-2-consultation/ | | 20 October 2026 | Consultation closes: national s106 templates for 10–49 home sites | https://energycount.co.uk/news/standard-s106-templates-medium-sites-consultation/ | | By end of 2026 | Mandatory water efficiency labelling for water-using products due | https://energycount.co.uk/news/mandatory-water-efficiency-labelling-2026/ | | 24 March 2027 | Future Homes Standard (Approved Document L 2026) and Approved Document F 2026 in force for non-higher-risk work; last day to notify under Part L 2021 | https://energycount.co.uk/guides/building-regulations-part-l/ | | 24 September 2027 | Future Homes Standard in force for higher-risk buildings (Gateway 2 applications before this date complete under Part L 2021) | https://energycount.co.uk/guides/future-homes-standard/ | | 24 March 2028 | Transitional deadline: buildings notified before 24 March 2027 must have commenced (foundations and ground-floor structure) to keep Part L 2021 | https://energycount.co.uk/news/future-homes-standard-transitional-deadline-commencement/ | | 30 April 2028 | Scotland: new-style EPCs required for marketing and letting (an existing EPC under ten years old is accepted for a first let until 30 April 2029) | https://energycount.co.uk/news/scottish-epc-reform-delayed-april-2028/ | ## GUIDES --- # Building Control has asked for a water calculation — what now? URL: https://energycount.co.uk/guides/water-calculation-building-control/ Updated: 2026-08-21 ## What they're asking for Every new dwelling in England and Wales — new builds, barn conversions, flat splits — must show that its calculated water use won't exceed **125 litres per person per day** (or [110 in some areas](/guides/110-litres-water-planning-condition/)). It's Part G of the Building Regulations, and the document Building Control wants is a short report using the official methodology: *The Water Efficiency Calculator for New Dwellings*. It is **not** a measurement or a site visit. It's a paper exercise based on the fittings you're installing: how much water your taps and showers flow, how big the bath is, how your WC flushes. Sensible modern fittings usually pass comfortably — see [how the 125 l/p/d figure works](/guides/125-litres-per-person-per-day/). ## What the document has to show There is no prescribed form, which is why submissions vary so much. What every building control body is looking for is the same short set of facts: - **The dwelling it applies to** — plot or house type, and which plots that type covers. - **The fittings schedule** — each fitting, the figure entered for it, and its unit: flow rates in litres per minute, flush volumes and bath capacity in litres, white goods in litres per kilogram and litres per place setting. - **The calculated figure** in litres per person per day, after the normalisation factor and the fixed external-use allowance have been applied. - **The target it is measured against** — 125, or 110 where planning says so — and a clear pass. - **The date and who produced it.** That is the whole document. On a site with several house types you need one per type, and one type covers every identical plot. ## When it's due Regulation 37 sets the backstop: the person carrying out the work must give notice of the calculated consumption to the local authority no later than **five days after the work has been completed**. Almost nobody should be working to that deadline, because the calculation depends on sanitaryware that gets specified and ordered months earlier. Most building control bodies ask for it with the plans or at first fix, and the sensible time to run it is **before the bathroom order goes in** — when a shower head is still a decision rather than a delivery. ## How the calculation actually works Each fitting is scored as **capacity × use factor + fixed use**. The use factors are published in Table 1 of the methodology and never change. The lines are added up, the total is multiplied by a **0.91 normalisation factor**, and a fixed **5 litres per person per day** of external use is added on the end. An ordinary specification — a 6/4 dual-flush WC, 6 l/min basin taps, a 180 litre bath with a 10 l/min shower over it, an 8 l/min kitchen tap and unspecified white goods — lands at **123.9 l/p/d**. Against a 125 target that is a pass with **1.1 litres to spare**. That margin is the thing worth understanding. A perfectly normal specification passes by barely a litre, so a late change — a bigger bath, a pumped shower, a waste disposal unit dropped into the kitchen design — can quietly turn a compliant scheme into a non-compliant one. The full arithmetic is set out in our [no-spreadsheet walkthrough](/tools/part-g-water-calculator/water-efficiency-calculator-spreadsheet/), fitting by fitting. ## Why calculations get sent back In rough order of how often it happens: 1. **The figures don't match the fittings.** A flow rate quoted from a brochure for a different pressure, or a spec that changed after the calculation was run. 2. **Multiple fittings averaged flat.** Where several showers or taps of different flow rates are fitted, the methodology takes the higher of the arithmetic average and **70% of the highest-flow fitting** — so one powerful master shower cannot be averaged away by a modest en-suite. 3. **The two adjustments missing.** Leaving out the 0.91 normalisation or the 5 l/p/d external allowance changes the answer by more than most specification changes do. 4. **The wrong target.** A planning condition required 110 and the calculation was run against 125. Check the decision notice, not the assumption. 5. **No plot schedule.** A calculation for "House Type B" with nothing saying which plots are House Type B. ## What it costs Online services and assessors typically charge **£25–£65 per calculation** — and again for each different house type on the site. There's nothing wrong with that, but the calculation itself is well within reach of anyone who can read a tap's specification sheet. ## Do it yourself, free Our [**WaterMonkey calculator**](/tools/part-g-water-calculator/) runs the full official methodology in your browser. Enter your fittings, watch the PASS/FAIL update live, and adjust until you're under target — all free. When you're happy, the Building Control-ready PDF report is **£25 +VAT**, and that covers every identical plot on your site. You only pay when it's right. What you'll need to hand: the flow rates (litres/minute) of your taps and showers, bath capacity to overflow, WC flush volumes, and your dishwasher and washing machine figures if they're being specified. All of it is on the product spec sheets or the retailer's listing. If you want to understand one line before you change it, start with [shower flow rate](/tools/part-g-water-calculator/shower-flow-rate/) — it's usually the biggest number on the page. ## Rather hand it off? If you'd prefer it done for you — or your case is complicated by rainwater harvesting, greywater reuse or a tight planning condition — our [Part G service](/services/part-g-water-calculations/) starts from a simple email with your sanitaryware list. Either way, the calculation shouldn't hold up your sign-off. --- # 125 litres per person per day, explained URL: https://energycount.co.uk/guides/125-litres-per-person-per-day/ Updated: 2026-08-21 ## Where the number comes from Part G of the Building Regulations caps a new dwelling's *calculated* water use at **125 litres per person per day**. Nobody meters your actual usage — the figure comes from the official methodology, which multiplies each fitting's consumption by a standardised "use factor" (how often a typical person uses it daily) and adds a fixed 5 litres for outdoor use. So a 9 litres/minute shower, a 180-litre bath, a 4/2.6-litre dual-flush WC and so on each contribute their share, and the shares must total ≤125. (Some areas use the tighter [optional 110 l/p/d standard](/guides/110-litres-water-planning-condition/) — check your planning conditions.) ## Which standard applies to you There are three numbers in circulation and only one of them applies to your project today. - **125 l/p/d** — the Building Regulations baseline for every new dwelling in England and Wales. This is your target unless something says otherwise. - **110 l/p/d** — the optional technical standard. It only applies where a **Local Plan policy or planning condition** imposes it, which is common across much of the south and east of England and standard practice in London. It is a planning route into a Building Regulations requirement, so the trigger is your decision notice, not your postcode. - **105 l/p/d** — **proposed, not in force.** Defra has consulted on cutting the baseline from 125 to 105 and the optional standard from 110 to 100. The consultation closed in December 2025 and the government response is still awaited; implementation is intended during 2026 with a six-month transitional period. We're tracking it in [Part G is heading for 105 litres](/news/part-g-105-litres-water-efficiency/). One thing not to assume: that a single national number is coming. The [August 2026 NPPF kept local water efficiency standards on the table](/news/nppf-2026-local-water-efficiency-standards/), including the possibility of something stricter than 110 in areas of serious water stress. For now, read the decision notice. ## Where the litres actually go The big three are **showers, WCs and baths** — together usually about two-thirds of the total. Taps and white goods matter less than people expect. Here is what an entirely ordinary specification looks like: a 6/4 dual-flush WC, 6 l/min basin taps, a 180 litre bath with a 10 l/min shower over it, an 8 l/min kitchen tap, and unspecified white goods. - Shower — **43.70** l/p/d before the final adjustments - WC, full and part flush together — **20.60** - Bath — **19.80** - Washing machine (default figure) — **17.16** - Kitchen taps — **13.88** - Basin taps — **11.06** - Dishwasher (default figure) — **4.50** That totals 130.70. Multiply by the 0.91 normalisation factor and add the fixed 5 litres of external use, and the answer is **123.9 l/p/d** — a pass, with 1.1 litres to spare. **That margin is the point of this page.** A normal specification passes by about a litre. Which is why a late change to the sanitaryware can turn a compliant scheme into a non-compliant one, and why running the numbers before the bathroom order goes in is worth ten minutes of anybody's time. ## Practical rules of thumb - **The shower is the lever.** Every litre per minute is worth roughly 4 l/p/d on the final figure. Dropping from 12 to 9 l/min usually fixes a fail on its own. See [shower flow rate](/tools/part-g-water-calculator/shower-flow-rate/). - **The part flush is worth twice the full flush.** The methodology assumes two part flushes for every full one, so a litre off the part flush is worth 2.69 l/p/d against 1.33 for the full. And a dual-flush WC beats a 6 litre single flush by about 5.4 l/p/d for no design compromise at all — see [WC flush volume](/tools/part-g-water-calculator/wc-flush-volume/). - **Basin taps repay more than kitchen taps.** A litre per minute off the basins is worth 1.44 l/p/d; the same litre at the kitchen sink is worth 0.40, because most of the kitchen line is a fixed allowance you can't design out. See [tap flow rates](/tools/part-g-water-calculator/tap-flow-rate/). - **A big bath is rarely fatal — unless there's no shower.** With a shower present the bath factor is only 0.11, so 10 litres of capacity is worth 1 l/p/d. Take the shower away and the factor jumps to 0.50, and the bath alone can eat two thirds of the allowance. See [bath capacity](/tools/part-g-water-calculator/bath-capacity/). - **Unspecified white goods cost you.** Leave them out and the methodology charges defaults of 8.17 l/kg and 1.25 l/place setting — about 19.7 l/p/d between them. Real specified appliances usually beat that. See [washing machines and dishwashers](/tools/part-g-water-calculator/washing-machine-and-dishwasher/). - **A waste disposal unit is a flat 2.80 l/p/d penalty** with nothing to offset it. Worth knowing before one appears late in the kitchen design. - **Offsetting is allowed.** Splash out on the shower and claw it back on WCs and taps. Rainwater or greywater systems are credited too, though they're rarely needed just to hit 125. ## See your own numbers The fastest way to understand it is to try it: our free [**WaterMonkey calculator**](/tools/part-g-water-calculator/) shows a live breakdown of where your litres go and a PASS/FAIL that updates as you change fittings. Experiment freely; the [Building Control-ready report](/guides/water-calculation-building-control/) is £25 +VAT when you're done. Or [we'll do it for you](/services/part-g-water-calculations/). --- # The 110 litres per person per day planning condition URL: https://energycount.co.uk/guides/110-litres-water-planning-condition/ Updated: 2026-08-21 ## Why your condition says 110, not 125 The Building Regulations' default water limit for new dwellings is [125 litres per person per day](/guides/125-litres-per-person-per-day/), but councils in water-stressed areas — much of the south and east of England — can require the **optional standard of 110 l/p/d** through a planning condition. If your decision notice mentions water efficiency, regulation 36(2)(b), or "110 litres", this is what it means. Building Control will then expect your [water calculation](/guides/water-calculation-building-control/) to demonstrate 110, not 125. It is worth being clear about the mechanism, because it catches people out: the tighter number arrives through **planning**, but it is discharged through **Building Regulations**. Nothing in Approved Document G changes automatically because of where you are building. The trigger is the condition on your permission, not your postcode — so read the decision notice rather than assuming. ## If you're building in London, your policy says 105 London Plan **Policy SI 5** requires residential development to achieve mains water consumption of **105 litres or less per person per day, excluding an allowance of up to five litres for external water consumption**. That looks like a third standard. It isn't. The Part G calculation adds a **fixed 5 l/p/d of external use at the very end**, after the normalisation factor. So: - **105 l/p/d excluding external use** (how London writes it), and - **110 l/p/d including external use** (how the Building Regulations optional standard writes it) are the same target, measured the same way. Run your calculation against 110 in the normal way and a London scheme is satisfied. The only thing to watch is that your submission makes clear which convention the figure on the front page uses, because a "105" and a "110" sitting in the same planning file have caused more than one unnecessary round of correspondence. The proposed national cut to **105 l/p/d** currently under consideration by Defra is a different thing again — that one is 105 *including* external use, and it isn't in force. See [Part G is heading for 105 litres](/news/part-g-105-litres-water-efficiency/) for where that stands. ## Is 110 hard to hit? Harder than 125 — the 15-litre haircut removes most of the slack — but very achievable with deliberate fitting choices rather than exotic kit. Start from the ordinary specification that lands at **123.9 l/p/d**: a 6/4 dual-flush WC, 6 l/min basin taps, a 180 litre bath with a 10 l/min shower, an 8 l/min kitchen tap and unspecified white goods. You need about **14 litres**. Here is one route: - **Shower 10 → 8 l/min** — saves **7.95 l/p/d**. The single biggest lever in the calculation. - **WC 6/4 → 4.5/3** — saves **4.69 l/p/d**. Most of it comes from the part flush, which the methodology weights twice as heavily as the full flush. - **Basin taps 6 → 5 l/min** — saves **1.44 l/p/d**. That is about **14 l/p/d** of savings. Run properly through the methodology the dwelling lands at **109.9 l/p/d** — a pass at 110, from three unremarkable specification decisions and no change to the layout. Other things that help, roughly in order of value: - **Specify the white goods.** Left blank, the calculation charges defaults of 8.17 l/kg and 1.25 l/place setting. Real appliances usually beat both — worth around 5 l/p/d where they're genuinely part of the handover. - **Aerated basin taps at 4 l/min** rather than 5, if the pressure suits. - **A standard-size bath** rather than a statement tub — though with a shower present this is worth only about 1 l/p/d per 10 litres of capacity, so it's a smaller lever than people assume. - **Don't fit a waste disposal unit.** It's a flat 2.80 l/p/d penalty with nothing to offset it. Where a client insists on the big shower or the big bath, the offsets have to come from everywhere else — or from **rainwater or greywater harvesting**, which the methodology credits and which sometimes turns an impossible spec into a pass. Both are capped at the demand they can actually displace, and the same WC demand can't be claimed twice across two systems. ## Check before you order sanitaryware The expensive mistake is buying fittings first and calculating second. Run your intended spec through our free [**WaterMonkey calculator**](/tools/part-g-water-calculator/) — set the target to 110, watch the live PASS/FAIL, and adjust before anything's ordered. There's a [110 l/p/d version of the calculator](/tools/part-g-water-calculator/110-litres/) already set to the tighter target, and fitting-by-fitting explainers for [showers](/tools/part-g-water-calculator/shower-flow-rate/), [WCs](/tools/part-g-water-calculator/wc-flush-volume/) and [taps](/tools/part-g-water-calculator/tap-flow-rate/) if you want to understand a line before you change it. The Building Control-ready report is £25 +VAT when you need it. Tricky condition wording or a marginal spec? [Send it to us](/services/part-g-water-calculations/) and we'll sort it. --- # What is Thermal Bridging? URL: https://energycount.co.uk/guides/thermal-bridging/ Updated: 2026-08-22 > **Quick answer:** a thermal bridge is a localised weak point — usually a junction like wall-to-floor or a window reveal — where heat escapes faster than through the surrounding fabric. Each junction's extra loss is measured as a **Ψ-value (psi value), in W/m·K**, calculated to BS EN ISO 10211. At modern insulation levels junctions can carry 20–30% of a dwelling's fabric heat loss. ## Thermal bridges: the weak points in the fabric A thermal bridge is a localised path through the building envelope where heat escapes more readily than through the surrounding fabric — typically at **junctions**: wall-to-floor, wall-to-roof, around windows and doors, at corners. Even with superb u-values everywhere else, poorly detailed junctions can account for 20–30% of a dwelling's fabric heat loss. There are two kinds. **Geometric bridges** — like an external corner, which simply has more exposed surface area than the flat wall. And **constructional bridges** — where a high-conductivity material (a concrete slab edge, a steel lintel, an uninsulated cavity closer) pierces the insulation line and carries heat straight through.
Section through a wall-to-floor junction showing the perimeter heat-loss path around the slab edge
Wall-to-floor: heat escapes around the slab edge.
Section through an eaves junction where the wall meets the roof, showing the thermal bridge
Eaves: where the wall meets the roof.
Plan through a window jamb junction showing heat loss around the window reveal
Window jamb: around the opening.
Plan through an external corner junction showing the thermal bridge at the corner
External corner: heat loss at the corner.
## Ψ-values (psi values) Each junction type has a **linear thermal transmittance**, or Ψ-value, measured in W/m·K — the heat loss per metre of junction per degree of temperature difference. In SAP and HEM, every junction length is multiplied by its Ψ-value and summed into the heat-loss calculation. A typical well-detailed junction sits around **0.02–0.08 W/m·K**; a poor one can be **0.15–0.30**. Because the lengths run for metres (a wall-to-floor junction runs the whole perimeter), small differences multiply quickly — which is why a SAP calculation with default Ψ-values can need noticeably more insulation or PV than one with calculated values. ### The maths in SAP (why a few hundredths matter) In SAP, junction heat loss is simply **length × Ψ-value**. A detached house has roughly 50 m of wall-to-floor junction around its perimeter. At a calculated 0.05 W/m·K that's 50 × 0.05 = **2.5 W/K**. With the punitive SAP default for that junction it's more like 50 × 0.15 = **7.5 W/K** — a 5 W/K difference that must be made up in better walls, more insulation or bigger PV. Across all your junctions, that gap is often the difference between a comfortable pass and a design rework. It's also why "measure the junction lengths, not just the wall area" is the first thing an assessor checks. ### What a good detail looks like The golden rules for every junction: **keep the insulation line continuous**, **avoid bridging it with high-conductivity material**, and **close cavities with insulated closers**. Concretely: - **Wall-to-floor** — edge insulation under the slab that meets the wall insulation; a DPC can't bridge the line. - **Window jamb/sill/lintel** — an insulated cavity closer with the frame set against the insulation line; a metal lintel with no thermal break is a classic failure. - **Eaves and gables** — loft or rafter insulation meeting the wall insulation without a gap. - **Corners** — nothing to fix structurally, but they're geometric bridges you can't remove — they just need to be *included* in the calculation, not forgotten. - **Party walls, balconies, exposed floors** — any element that penetrates the envelope needs a thought-through detail; balconies are the notorious one. Each junction type has a page showing how to model it in ΨMonkey — from [wall-to-floor](/tools/psi-calculator/wall-to-floor/) and [window jambs](/tools/psi-calculator/window-jamb/) to [balconies](/tools/psi-calculator/balcony/) and [exposed floors](/tools/psi-calculator/exposed-floor/). ## Which junctions cost you most SAP / Approved Document L labels each junction with an "E-number" reference, and they're all modelled in our free [ΨMonkey psi calculator](/tools/psi-calculator/): - **[Wall-to-floor (E5)](/tools/psi-calculator/wall-to-floor/)** — runs the whole heated perimeter; usually the biggest single contributor. - **[Eaves (E9/E10)](/tools/psi-calculator/eaves/)** and **[gable (E11/E12)](/tools/psi-calculator/gable/)** — where the wall meets the roof. - **[Window jamb (E4)](/tools/psi-calculator/window-jamb/)**, **[sill (E3)](/tools/psi-calculator/window-sill/)** and **[lintel (E1/E2)](/tools/psi-calculator/lintel/)** — around every opening; jamb and sill lengths add up fast on glazed elevations. - **[External corner (E13)](/tools/psi-calculator/external-corner/)** and **[inverted corner (E14)](/tools/psi-calculator/inverted-corner/)** — geometric bridges. - **[Intermediate floor (E6)](/tools/psi-calculator/intermediate-floor/)** and **[party wall (E15)](/tools/psi-calculator/party-wall/)** — for flats, terraces and semi-detached homes. - **[Balcony (E8/E24)](/tools/psi-calculator/balcony/)** and **[exposed floor (E20/E21)](/tools/psi-calculator/exposed-floor/)** — balconies and floors over voids are classic constructional bridges. ## Your three options in SAP 1. **Default values** — punitive, and they make passing harder and more expensive. 2. **Accredited/standard details** — better, if your details exactly match the published ones ([more on ACDs](/guides/accredited-construction-details/)). Note that SAP 10 removed Accredited Construction Details over accuracy concerns, leaving manufacturer schemes or calculated values. 3. **Calculated Ψ-values** — modelled to BS EN ISO 10211. Almost always the best result, often the cheapest route to compliance. ## Calculate your own Ψ-values Our free in-browser tool, [**ΨMonkey**](/tools/psi-calculator/), models junctions with a finite-difference solver to BS EN ISO 10211 and gives you the Ψ-value and f_Rsi temperature factor. Use it to test your details — PDF reports for Building Control are £25 a junction. The process: 1. **Model the junction** — paint the build-up (walls, floors, roof, insulation lines, cavities, DPC) on the grid. 2. **Solve** — ΨMonkey runs the 2-D heat-flow calculation and returns the Ψ-value and the coldest-surface temperature factor. 3. **Iterate** — move the insulation line, change the closer, compare details until the number is good. 4. **Export** — the branded PDF carries the parameters, the result and a unique Report ID that [Building Control can verify](/verify/). 5. **Hand to your SAP assessor** — calculated values slot straight into the [SAP calculation](/services/sap-calculations/) as an alternative to defaults. ## Condensation risk: f_Rsi Thermal bridges aren't just about heat loss. A cold internal surface at a junction invites condensation and mould. The **temperature factor f_Rsi** (0 to 1) measures how cold the worst internal surface gets; Building Regulations require f_Rsi ≥ 0.75 for dwellings. ΨMonkey reports it automatically — and the same junction that leaks heat is usually the one that risks mould, so fixing the detail fixes both. ## The bottom line Get the [U-values](/guides/u-values/) right, then get the junctions right — calculated Ψ-values are frequently the cheapest single route to a [SAP 10](/guides/sap-10-whats-new/) pass, and they de-risk your [compliance pack](/services/sap-calculations/compliance-pack/). Model yours free with [ΨMonkey](/tools/psi-calculator/) — no subscription, no sign-up. --- # Why two U-value calculators give different answers for the same wall URL: https://energycount.co.uk/guides/why-u-value-calculators-disagree/ Updated: 2026-09-02 Run the same wall through two different online calculators and you will often get two different numbers. Sometimes the gap is trivial. Sometimes it is enough to move a design from passing to failing. Either way it is corrosive: if the answer changes with the website, none of them feel trustworthy. It is not confined to U-values. Discussing thermal-mass tools, contributors on the Green Building Forum found that different calculators produced *"very different results for decrement delay"* for the same construction — and were left unsure which model to believe. The reassuring part is that the calculators are usually not broken. A U-value is the output of a method with several inputs, and two tools can each be arithmetically correct while disagreeing, because they made different assumptions about those inputs. There are five places the difference nearly always hides. ## 1. The bridging fraction This is the big one, and on a framed wall it will usually account for most of any gap. Studs, joists and rafters conduct far better than the insulation between them, so the calculation has to know what proportion of the area they occupy. On a timber frame wall at 600mm centres with 38mm studs, the timber is not simply 38 ÷ 600 — you have to include noggins, top and bottom plates, lintels and the extra studs at openings, which is why the figure used in practice is typically higher than the naive one. Move that fraction from 0.09 to 0.15 and a 140mm mineral wool wall moves by roughly 0.02 to 0.03 W/m²K. That is the whole margin on a 0.18 target. **How to check:** find where each calculator states its fraction. If one of them never asked you, it assumed one. ## 2. Whether the combined method was used at all Once anything bridges an insulation layer, resistances cannot just be added up. BS EN ISO 6946 requires two separate calculations: - an **upper limit**, treating heat as flowing down parallel paths (through timber, through insulation) that do not interact - a **lower limit**, treating each bridged layer as a single equivalent layer The answer is the average of the two. A tool that adds a single column of resistances is not doing this, and on a bridged element it will read optimistic. **How to check:** a calculator following the method can show you both limits. If it only ever shows one total resistance and your wall has studs in it, that is your answer. ## 3. The ΔU corrections BR 443 adds small allowances to the finished U-value: - for **air gaps** in or around the insulation layer, depending on how well it is installed and whether it is continuous - for **mechanical fixings** that penetrate the insulation They are usually between 0.00 and 0.04 W/m²K. Individually small; collectively the difference between a pass and a fail on a tight target. They always make the number worse, they are easy to leave out, and plenty of free calculators leave them out. **How to check:** look for ΔU as its own line. If it is not shown, assume it was not applied. ## 4. Surface resistances and the direction of heat flow Every element has an internal and external surface resistance, and they depend on which way the heat is going: | Element | Rsi | Rse | |---|---|---| | Wall (horizontal) | 0.13 | 0.04 | | Roof (upward) | 0.10 | 0.04 | | Floor (downward) | 0.17 | 0.04 | Use wall values on a roof and the answer shifts. There is a second trap here too: if the build-up contains a **well-ventilated cavity**, ISO 6946 §6.9.4 requires the cavity and every layer outside it to be disregarded entirely, with Rse replaced by Rsi. A calculator that quietly includes the outer leaf in that situation will give a much better — and wrong — answer. ## 5. The λ values themselves A generic value for "mineral wool" and a manufacturer's declared value for a specific product are not the same number. Declared values are revised. Some products have thickness-dependent λ, so the same board is 0.027 at 50mm and 0.025 at 100mm. And a fair few online calculators carry values with no stated origin at all. **How to check:** every material should show where its figure came from and when it was taken. If a calculator cannot tell you that, its answer cannot be audited — and an unauditable number is a poor thing to attach to a Building Regulations submission. ## So which one is right? Work through the five in order. In our experience the difference is found by the second or third on almost every occasion, and it is nearly always a bridging fraction or a missing correction. Then apply the harder test: **which calculator will show you its working?** A tool that prints the method, every layer with its thickness and λ, both resistance limits, the corrections applied and the source of every material can be checked by you, by a Building Control officer, or by whoever inherits the file in five years. A tool that prints a number cannot. That is the difference that matters, and it is why U-Monkey shows the full substitution — `R = d ÷ λ` with the actual figures in place — and puts a verifiable report ID on every report, including the free ones. --- *Sources: discussion of calculator discrepancies and thermal-mass tools on the [Green Building Forum](https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16112); material-matching and vapour-unit difficulties on [BuildHub](https://forum.buildhub.org.uk/topic/8021-online-condensation-analysis/). The calculation requirements described here are from BS EN ISO 6946:2017 and BR 443 (2019).* --- # Building Regulations Part L Explained URL: https://energycount.co.uk/guides/building-regulations-part-l/ Updated: 2026-09-04 > **Quick answer:** Part L is the section of the Building Regulations (England) covering the conservation of fuel and power — the energy performance rules for new and existing buildings. As of September 2026 the edition in force is **Part L 2021**, assessed with **SAP 10.3**; the Future Homes Standard edition applies to new schemes from **24 March 2027**. A new dwelling complies by passing four SAP tests at once, then proving it as built with photographs, a compliance report and an EPC. ## What Part L is Requirement L1 of Schedule 1 to the Building Regulations 2010 says, in essence, that reasonable provision must be made for the conservation of fuel and power in buildings. **Approved Document L** is the government's guidance on how to meet it, and it is where the numbers live. Since the 2021 edition it comes in two volumes: **Volume 1: Dwellings**, covering new *and* existing homes, and **Volume 2: Buildings other than dwellings**. The old names — L1A for new dwellings, L1B for existing ones, L2A and L2B for other buildings — were retired in 2021, although the paperwork and half the industry still use them. Which volume you are under decides which calculation you need. Volume 1 work is assessed with [SAP](/services/sap-calculations/); Volume 2 work with [SBEM](/services/sbem-calculations/). ## Which edition applies to my project? This is where most of the confusion lives. The picture in England: - **Part L 2013** — introduced the fabric energy efficiency target. **Fully revoked**: its transitional window closed on 15 June 2023. - **Part L 2021** — the edition **in force today**, applying to work from **15 June 2022**. It targets roughly a 31% carbon improvement over 2013 as a stepping stone to net zero. Assessed with **SAP 10.3**, which became the sole approved methodology on 24 March 2026, replacing SAP 10.2. - **Approved Document L 2026** — the [Future Homes Standard](/guides/future-homes-standard/), published 24 March 2026 and **in force from 24 March 2027** (24 September 2027 for higher-risk buildings). Projects with a building notice or full plans submitted before 24 March 2027 can build to the 2021 standards if work starts on site by **24 March 2028**. If your scheme straddles a date, the question is when it was notified and when it starts, not when it finishes. The transitional protection works **building by building**, not site by site: starting one plot does not protect the rest of the scheme. And "started" has a legal meaning since October 2023 — for a new building it is the point at which the foundations and the structure of the ground floor are complete, not site clearance or the first pour.

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## Part L for new dwellings: the four tests It is easy to think of Part L as "the carbon test". A new dwelling has to clear **four hurdles at once**: | Test | Metric | What it means | | --- | --- | --- | | Primary energy | DPER ≤ TPER | The headline target in Part L 2021 — total primary energy demand | | Carbon | [DER ≤ TER](/guides/der-ter/) | CO₂ emissions per m² per year | | Fabric efficiency | [DFEE ≤ TFEE](/guides/fabric-energy-efficiency/) | Fabric-only heat demand — cannot be bought back with renewables | | Limiting standards | Backstop values | Every U-value, the air permeability and the fixed services within their limits | The targets come from a **notional dwelling** the same size and shape as yours, built to a reference specification: walls 0.18, floors 0.13, roof 0.11 and windows 1.2 W/m²K; air permeability 5; a gas boiler at 89.5%; waste water heat recovery; and — the one that surprises people — **solar PV sized at 40% of the ground floor area divided by 6.5**. That is why fabric improvements alone rarely get a modern dwelling through without [PV](/guides/solar-pv/) or a [heat pump](/guides/air-source-heat-pumps/). The limiting values are the other half — nothing worse than a wall at 0.26, a floor at 0.18, a roof at 0.16, windows and doors at 1.6, rooflights at 2.2, or an air permeability of 8 — and a dwelling built merely to those will fail the targets by a distance. The full detail is on the [U-values guide](/guides/u-values/). ## Proving it: notices, the BREL report and the photographs The 2021 edition put a process around the calculation, and this is the part people searching for "Part L compliance" usually need. **Before work starts**, the regulations require the target rates, the as-designed rates and a **list of the specifications** the calculation depends on to be notified to Building Control — by the day before work begins — on the design-stage **BREL report** (Building Regulations England Part L compliance report). **Within five days of completion**, the as-constructed rates and any changes to that specification list are notified on the completion-stage BREL, signed by the assessor and the builder. The homeowner gets a copy of each. The completion BREL is accompanied by **photographic evidence** — new in 2021, and the thing most often missing at the end. Every dwelling needs its own set, showing the insulation continuous and properly installed at six stages: the foundations and ground floor; each external wall type; each roof type; each opening type including the reveals and cavity closers; the airtightness details; and the building services, including pipework insulation. They are normally taken by the builder, need to be date-stamped and located, and are reviewed by the SAP assessor against the specification before the report is signed. There is no way to photograph insulation that has been plastered over, so the site team needs to know on day one. Then the **EPC**, produced from the as-built SAP by an accredited on-construction assessor and given to the owner within five days of completion, and the **home user guide** for the occupier. Building Control cannot issue the completion certificate without the EPC. ## The other things Part L 2021 asks of a new dwelling **Air tightness.** [Every new dwelling is tested](/services/air-tightness-testing/) — sample testing ended in 2022 — and the measured result goes into the as-built SAP. **Lighting.** Fixed internal lighting should have lamps of at least **75 lumens per circuit-watt**, with local controls per space; fixed external lighting needs daylight-responsive switch-off, and occupancy control where the efficacy is 75 or below. The notional dwelling assumes 80. **Heating design.** A design flow temperature of 55°C or lower is what the notional dwelling assumes, which is why radiators are getting bigger and why [heat pumps](/guides/air-source-heat-pumps/) fit the standard so naturally. **Thermal bridging.** Junction heat losses are assessed separately from U-values, as Ψ-values, and SAP's default values are punitive. Calculating your actual junctions — which the free [ΨMonkey psi value calculator](/tools/psi-calculator/) does to BS EN ISO 10211 — is usually the cheapest improvement available; the alternative is to build to [Recognised Construction Details](/guides/accredited-construction-details/), the scheme that replaced Accredited Construction Details under SAP 10. **Overheating is a separate requirement.** Since June 2022 a new dwelling also has to pass [Part O](/guides/building-regulations-part-o/) — glazing limits and free-area rules on the drawings, or TM59 modelling — assessed alongside the SAP, not inside it. ## Part L for existing dwellings Work to existing homes — [extensions](/services/sap-calculations/extensions/), [conversions](/services/sap-calculations/conversions/), renovations, replacement windows — falls under Volume 1 too, but without the target-rate machinery. New thermal elements must meet the limiting values for new elements in existing dwellings: walls **0.18**, floors **0.18**, roof **0.15**, windows and doors **1.4**, rooflights **2.2**. Retained elements being renovated must be brought from a threshold to an improved value where that is feasible and pays back within 15 years. And every window and door in an existing dwelling has to meet 1.4 on its own — they are excluded from area-weighting. **Extensions** comply on those U-values provided the windows, doors and rooflights stay within **25% of the extension's floor area** plus the area of any existing openings the extension covers ([check yours here](/services/sap-calculations/extensions/#glazing-checker)). Exceed it and there are two routes to showing reasonable provision — an area-weighted U-value calculation, or a [whole-dwelling SAP](/services/sap-calculations/extensions/) in which improvements to the existing house offset the extra glazing. A **conservatory** escapes Part L only if it is at ground level, no more than 30 m², thermally separated from the house and not on the house's heating system. **Conversions** — a material change of use creating a dwelling — bring Part L in full, but with no target emission rate; compliance is element by element, and a [SAP](/services/sap-calculations/conversions/) is the usual way to show the trade-offs when a retained stone wall cannot reach the improved value. ## Part L for other buildings Volume 2 does the same job for offices, retail, industrial and everything else that is not a dwelling, with [SBEM](/services/sbem-calculations/) as the calculation, a BRUKL report in place of the BREL, its own limiting standards, and the same design-stage and as-built duties. The commercial EPC is a separate duty on completion. Volume 2's 2026 edition lands on the same dates as Volume 1's. ## What changes under the Future Homes Standard The biggest shake-up to Part L in over a decade lands with **[Approved Document L 2026](/guides/future-homes-standard/)** — retitled "Energy and greenhouse gas emissions". For dwellings: - **In force 24 March 2027**, with the transitional buffer above. - Roughly a **75% cut in carbon emissions** against a 2013 baseline home — effectively the end of new-build gas boilers, with heat pumps the default. - A **new requirement L3** making on-site renewable electricity — solar PV — a legal requirement for new dwellings, rather than something the notional dwelling merely assumed. - A tighter **air permeability** in the notional dwelling. The **limiting U-values do not change**; anyone expecting new backstops will find the same numbers, renumbered. - **SAP 10.3** is the compliance methodology at launch; the [Home Energy Model](/guides/future-homes-standard/) follows later and eventually replaces it. Tighter airtightness and a heat-pump baseline make [thermal bridging](/guides/thermal-bridging/) matter *more*, not less. Designing now? The SAP 10 decisions — good fabric, PV, low-carbon heating, [calculated Ψ-values](/tools/psi-calculator/) — are exactly the ones the Future Homes Standard requires. ## Wales and Scotland **Wales** has its own Approved Document L, 2022 edition, in force since **23 November 2022**, with its own tighter carbon target for new homes and its own approval of the SAP methodology; the process — design-stage and as-built calculations, testing of every dwelling, the EPC — is the same shape as England's. **Scotland** has no Part L. The equivalent is **Section 6 (Energy)** of the Building Standards Technical Handbook, with revised standards for building warrants from **1 February 2023**, assessed with SAP 10 under a target emissions rate of its own. ## The bottom line Part L is four tests dressed as one, followed by a paper trail — and the target moves with your dwelling's shape, so the earlier you model it, the cheaper compliance is. Whether you are on Part L 2021 today or planning for the [Future Homes Standard](/guides/future-homes-standard/), the fundamentals are the same: good fabric first, then renewables, and photographs of the insulation before it disappears. Unsure which requirements apply to your project? [Ask us](/contact/) — it is quicker than reading the Approved Documents — or get your [SAP calculations](/services/sap-calculations/) under way. --- # What is PHPP (and when do you actually need it)? URL: https://energycount.co.uk/guides/phpp-energy-statements/ Updated: 2026-06-21 ## What PHPP is **PHPP** — the Passive House Planning Package — is an energy model developed by the Passivhaus Institute. It predicts a building's **space heating demand** and **total energy use** far more reliably than a Part L [SAP calculation](/services/sap-calculations/), because it models the building physics in much greater detail. Post-occupancy studies consistently show PHPP gets close to real-world performance, where SAP can drift. ## When you actually need it for planning Most planning energy conditions are still satisfied with a standard [energy statement](/services/energy-statements/) and a modest renewables contribution. But a wave of authorities have moved to tougher, **energy-based net-zero targets** — typically a space heating demand of around 15–30 kWh/m²/yr and an Energy Use Intensity (EUI) cap of around 35–40 kWh/m²/yr, covering all the energy a building uses. SAP wasn't built to demonstrate those figures, so these councils run their own **energy summary tools** that are populated from PHPP modelling. If your site is in one of these areas, PHPP is effectively the entry ticket: - **Cornwall** — SEC1 Energy Summary Tool (Climate Emergency DPD) - **Bath & North East Somerset** — Energy Summary Tool 2, required for developments of 10+ dwellings - **Central Lincolnshire** — Local Plan Policy S6 - **Greater Cambridge** — Policy CC/NZ ## PHPP for planning is *not* Passivhaus certification This is the bit that trips people up. Using PHPP to **demonstrate a planning energy target** is not the same as **certifying a building to the Passivhaus standard**. Certification is a separate, more demanding process — design scrutiny, airtightness targets, certified-product detailing and sign-off — and it's run by certified Passivhaus designers. You can (and often must) use PHPP modelling to satisfy these planning policies *without* pursuing the Passivhaus badge. If you do want the badge as well, you'll want a certified Passivhaus designer on the team for that side of it. ## How this fits your project The practical upshot: in these areas, [fabric performance](/guides/fabric-energy-efficiency/) and [u-values](/guides/u-values/) matter even more, and the energy statement is a more involved piece of work that's best started early — before the design is fixed. We run the PHPP modelling for these planning energy targets and produce the statement in-house, so the modelling and the planning report come from one place. Got a condition that mentions space heating demand, EUI, or an energy summary tool? [Send it over](/contact/) and we'll tell you exactly what's needed — see our [energy statements service](/services/energy-statements/) for more. --- # SAP 10: What's New in Part L 2021? URL: https://energycount.co.uk/guides/sap-10-whats-new/ Updated: 2026-09-04 ## What SAP actually is SAP (Standard Assessment Procedure) is the government's methodology for rating the energy performance of dwellings — the engine behind Energy Performance Certificates, [Building Regulations Part L](/guides/building-regulations-part-l/) compliance, and most planning conditions. A trained assessor builds a model of your dwelling — fabric, heating, hot water, ventilation, lighting, renewables — and SAP turns it into the numbers that decide whether you pass: the **DER/DPER** (dwelling emission rate) against the **TER/TPER** target ([plain-English guide](/guides/der-ter/)). SAP 10 is the current methodology; this page is about the changes it brought in 2021–22. ### Who needs a SAP assessment You'll hit SAP in four places: **Building Regulations compliance** for new dwellings (Part L 1A) and material works to existing ones (Part L 1B); the **EPC** you must hand over on completion or sale; **planning conditions** on many developments (especially via [energy statements](/services/energy-statements/)); and increasingly **mortgage/valuation and net-zero policies** on new homes. Our [SAP calculations service](/services/sap-calculations/) covers all of them — and the [New Build Compliance Pack](/services/sap-calculations/compliance-pack/) bundles SAP with the [water](/services/part-g-water-calculations/), [acoustics](/services/sound-testing/) and [air-tightness](/services/air-tightness-testing/) evidence most schemes need anyway. ## The headline Part L 2021 went live on 15 December 2021 and has applied to all developments registered after **15 June 2022**. It targets a **31% improvement in CO₂ emissions** over Part L 2013, achieved through better fabric plus renewables and low-carbon energy in the target calculation. The assessment tool is **SAP 10**, successor to SAP 2012. ## A much tougher notional dwelling The notional dwelling that sets your targets (TER/TPER) is far tighter in SAP 10: | Element | Notional u-value (TER) | Maximum u-value allowed (DER) | | --- | --- | --- | | Walls | 0.18 | 0.26 | | Floor | 0.13 | 0.18 | | Roof | 0.11 | 0.16 | | Doors | 1.0 | 1.6 | | Windows | 1.2 | 1.6 | | Fully-glazed doors | 1.2 | 1.6 | | Roof windows | 1.2 | 1.4 | Plus: air test target of 5.0, waste water heat recovery to all showers, an 89.5%-efficient gas boiler, and 80 lm/W lighting. To pass, your [DER and DPER](/guides/der-ter/) must beat the targets — exceed any notional value and you'll need to offset it elsewhere. ## The big one: PV in the notional dwelling SAP 10's notional dwelling assumes PV is installed — for houses, kW of PV = 40% of the ground-floor area ÷ 6.5 (for flats, 40% of the flat's floor area ÷ 6.5 ÷ the number of storeys in the block). That's roughly **4kW for an average dwelling**. In our experience fabric improvements alone won't get most dwellings through SAP 10: the practical routes to a pass are [solar PV](/guides/solar-pv/) or a [heat pump](/guides/heat-pumps/). It's a deliberate policy choice — the target assumes you're generating — and it's the change that surprises most people new to SAP 10. ## Other changes worth knowing **Electricity's carbon factor fell from 0.519 kgCO₂/kWh to 0.136** — below mains gas (0.210) for the first time, reflecting the greener grid. SAP 10.0 (2018) had cut it to 0.233; SAP 10.1 and SAP 10.2 took it to 0.136, applied month by month rather than as one flat figure, and SAP 10.3 — the approved methodology since 24 March 2026 — uses a forward-looking 0.086 against 0.214 for gas, with electricity's primary energy factor rising to 1.969. All-electric designs, brutal to pass under SAP 2012, now have far more flexibility. It's why heat pumps, [MVHR](/guides/mvhr/) and efficient electric hot water have become so common in new-build specs. **Thermal bridging options changed.** SAP 10 removed Accredited Construction Details over accuracy concerns. That leaves manufacturer schemes — or bespoke calculated Ψ-values for each junction, which is exactly what our [ΨMonkey psi calculator](/tools/psi-calculator/) produces. [More on thermal bridging](/guides/thermal-bridging/). **Heating pattern** — now a consistent daily pattern instead of different weekday/weekend assumptions, reducing modelled energy use. Heat network loss factors increased, which matters for London planning carbon targets. **Lighting** — proper lighting design now feeds the calculation (like SBEM), recognising high-efficacy LED products. **Hot water** — shower flow rates are now entered, creating crossover with [Part G water calculations](/services/part-g-water-calculations/). **PV configuration matters** — flats only benefit from PV they're directly connected to; landlord-supply-only arrangements no longer count for every flat. Battery storage and PV diverters can now be included, and MCS overshading data can replace defaults. **Fabric & services beyond the table** — [fabric energy efficiency](/guides/fabric-energy-efficiency/), the [energy hierarchy](/guides/energy-hierarchy/) and [fuel choice in SAP](/guides/fuel-choice-in-sap/) all interact with the target: better fabric shrinks the PV/heat-pump requirement; the right fuel choice changes the whole calculation. ## What this means for you Design for SAP 10 from day one: realistic fabric, PV or heat pump from the start, and calculated junction Ψ-values instead of defaults. Our [SAP team](/services/sap-calculations/) can model your options. ## Where it's going: the Future Homes Standard SAP 10 is the stepping stone to the [**Future Homes Standard**](/guides/future-homes-standard/) — and that's no longer a distant "someday." [Approved Document L 2026](/news/future-homes-standard-adl-2026/) was published on 24 March 2026 and **comes into force on 24 March 2027**, effectively ending new-build gas boilers and making on-site renewables a requirement, with **SAP 10.3** the compliance methodology at launch (the [Home Energy Model](/news/home-energy-model-launch-delayed/) follows later). If you're designing now, the SAP 10 decisions — fabric, PV, heat pumps, low-carbon heating — are exactly the decisions the FHS will require. The [energy statements](/services/energy-statements/) and [PHPP](/guides/phpp-energy-statements/) worlds are converging on the same place. ## SAP 10 vs SAP 2012 at a glance | Change | SAP 2012 | SAP 10 | | --- | --- | --- | | Electricity carbon factor | 0.519 kgCO₂/kWh | 0.233 in SAP 10.0 → 0.136 in SAP 10.2 → 0.086 kgCO₂/kWh in SAP 10.3 (from 24 March 2026) | | PV in the notional dwelling | No | Yes (~4 kW typical) | | Accredited Construction Details | Accepted | Removed — manufacturer schemes or calculated Ψ-values | | Heating pattern | Weekday/weekend profiles | Consistent daily pattern | | Shower flow rates | Not modelled | Entered into the calculation | | Lighting | Default assumptions | Lighting design feeds in (like SBEM) | | WWHR | Optional | Assumed on all showers in the notional dwelling | | Air-tightness target | 5.0 m³/h/m² | 5.0 m³/h/m² | ## Quick facts - Carbon factors in SAP 10.3 (the approved methodology since 24 March 2026): electricity **0.086**, gas **0.214** kgCO₂e/kWh — down from 0.136 and 0.210 in SAP 10.2, and 0.233 for electricity in SAP 10.0. Primary energy factors: electricity 1.969, gas 1.12. - Notional PV for a house: 40% of lowest storey area ÷ 6.5. - Air-tightness target in the notional dwelling: 5.0 m³/h/m². - WWHR assumed on all showers in the notional dwelling. - Calculated junction Ψ-values (BS EN ISO 10211) beat SAP defaults — often the cheapest route to a pass. Further reading: [BRE SAP 10](https://bregroup.com/sap/sap10) and [Approved Document L](https://www.gov.uk/government/publications/conservation-of-fuel-and-power-approved-document-l). --- # Building Regulations Part O explained URL: https://energycount.co.uk/guides/building-regulations-part-o/ Updated: 2026-09-04 > **Quick answer:** Part O (Overheating) applies to every new residential building in England notified since **15 June 2022** — not to extensions or conversions. A home complies either by the **simplified method** (glazing capped at 11–18% of floor area depending on orientation, location and cross-ventilation, plus a minimum free area of openings) or by **dynamic thermal modelling to CIBSE TM59**, which is what you need when the glass exceeds the tables or the windows cannot be assumed open at night — the 40 dB bedroom-noise rule is the usual trigger. Mechanical cooling comes last, after every passive measure. ## What Part O is For decades the Building Regulations cared about keeping heat in. **Requirement O1**, added to Schedule 1 in 2021 and in force from 15 June 2022, is the first to care about keeping it out. It says that reasonable provision must be made in a new residential building to *limit unwanted solar gains in summer* and to *provide an adequate means to remove heat from the indoor environment*. **Approved Document O** is the government's guidance on how to do that, and it is a short document with two routes through it. The trigger was straightforward: better-insulated, more airtight homes with large areas of glass were overheating, and the 2022 heatwaves made the point. Part O sits alongside [Part L](/guides/building-regulations-part-l/) rather than inside it — a home has to pass both — and it is assessed separately, by an overheating assessment rather than a SAP calculation. ## Who it applies to **New residential buildings only.** New dwellings, and new institutions and other buildings with rooms for residential purposes — care homes, student halls, boarding accommodation — but not hotel rooms. A conservatory built as part of a new home is inside the requirement; one added later is not. Extensions, loft conversions and a **material change of use** — an office turned into flats, a barn into a house — are outside it altogether, however glassy they are. That surprises people, because it is precisely the conversions with floor-to-ceiling glazing that overheat; but the regulation is written around buildings that are *erected*. Part O also does not apply in Wales or Scotland in this form (see below), and it is not retrospective. ## The two routes **The simplified method** (Section 1 of Approved Document O) is a check you can do on the drawings: is the glazing under a limit, and do the windows and other openings give enough free area to purge heat? No modelling, no software, no weather file. If a design meets the limits, that is the evidence. **Dynamic thermal modelling** (Section 2) is a computer model of the dwelling — its fabric, glazing, shading, ventilation and occupancy — run through a design summer to the **CIBSE TM59** methodology, which sets the pass criteria. It costs more and takes longer, but it can pass designs the simplified method cannot, because it credits what the simplified method ignores: thermal mass, external shading, secure night ventilation, the real orientation of every window. The assessor chooses the route, and the choice is usually made for them by three questions: where is the site, which way does the glass face, and can the windows be left open at night? ## The simplified method, step by step ### 1. Location Approved Document O splits England in two. A **high-risk location** is one of the urban and suburban **London postcode districts listed in Appendix C**, where night-time temperatures stay high and the urban heat island bites; everywhere else is a **moderate-risk location**. The official FAQ adds that central Manchester also has elevated night temperatures — its minimum standard is the moderate-risk one, but designers are pointed at the high-risk figures for the postcodes it lists. ### 2. Cross-ventilation A dwelling is cross-ventilated when it has openings on **opposite façades**, so air can be driven through it. A house usually is; a single-aspect flat is not; a corner flat with windows on two adjacent walls does not count either. Cross-ventilation earns more generous glazing limits and lower free-area requirements, because the heat has somewhere to go. ### 3. The glazing limit Find the **largest glazed façade** and its orientation, to the nearest compass point (if it sits exactly between two, use the stricter). Then read the maximum glazing area from Table 1.1 or 1.2 — as a percentage of the **floor area of the dwelling**, with a second, tighter cap on the **most glazed room** as a percentage of that room's floor area. Glazing means the transparent area — glass, not frames. **Table 1.1 — cross-ventilated** (Approved Document O, 2021 edition): | Largest glazed façade | High risk: % of floor area | High risk: most glazed room | Moderate risk: % of floor area | Moderate risk: most glazed room | | --- | --- | --- | --- | --- | | North | 15% | 37% | 18% | 37% | | East | 18% | 37% | 18% | 37% | | South | 15% | 22% | 15% | 30% | | West | 18% | 37% | 11% | 22% | **Table 1.2 — not cross-ventilated:** | Largest glazed façade | High risk: % of floor area | High risk: most glazed room | Moderate risk: % of floor area | Moderate risk: most glazed room | | --- | --- | --- | --- | --- | | North | 15% | 26% | 18% | 26% | | East | 11% | 18% | 18% | 26% | | South | 11% | 11% | 15% | 15% | | West | 11% | 18% | 11% | 11% | Two things jump out. West is the enemy: low afternoon sun arrives when the house is already warm, which is why a west-facing, single-aspect flat is capped at 11% of its floor area. And some high-risk figures are *more* generous than the moderate-risk ones — because in a high-risk location the glazing also has to be shaded (next step), and the tables assume it is. For scale: a 90 m² house with 18% glazing has 16 m² of glass in total, and a 20 m² living room capped at 37% can have 7.4 m² of it. A south-facing rear elevation with bifolds across the full width will usually blow through the room cap before it troubles the whole-dwelling figure. ### 4. Shading (high-risk locations) In a high-risk location, glazing facing anywhere between north-east and north-west through south — in other words everything but a northerly aspect — must be shaded: external shutters that still allow ventilation, glazing with a **g-value no higher than 0.4** and a light transmittance of at least 0.7, or, for south-facing glazing only, an overhang that cuts the sun off entirely once it reaches 50° above the horizon. Internal blinds do not count. ### 5. Free area for removing heat Limiting the gain is half the requirement; the other half is getting rid of what still comes in, and the simplified method does that with **minimum free areas** — the actual open area of windows and other openings when opened as designed (Appendix D shows how to work it out from the opening angle), not the size of the frame. | | High risk | Moderate risk | | --- | --- | --- | | **Cross-ventilated** — total free area, whole dwelling | the greater of 6% of floor area or 70% of the glazing area | the greater of 9% of floor area or 55% of the glazing area | | — bedroom minimum | 13% of the room's floor area | 4% of the room's floor area | | **Not cross-ventilated** — total free area | the greater of 10% of floor area or 95% of the glazing area | the greater of 12% of floor area or 80% of the glazing area | | — bedroom minimum | 13% of the room's floor area | 4% of the room's floor area | Note the trap: the free-area requirement is tied to the *glazing* area, so a design that maximises glass right up to the limit needs a great deal of it to open — and a window that only opens 100 mm on a restrictor provides a small fraction of its frame size as free area. ### What fails the simplified method The same things every time: a glazed rear elevation facing south or west; single-aspect flats, especially in London; fixed glazing and picture windows that add to the glazing total without adding any free area; and bedrooms with one small opening. And then there is the case where the numbers pass on paper but the assumption behind them does not hold — which is the next section. ## Noise, security and the windows you cannot open The simplified method's free areas assume the windows are **open at night**. Approved Document O says plainly that they will not be if bedroom noise with them open would exceed **40 dB LAeq averaged over 11pm to 7am**, or **55 dB LAFmax more than ten times a night** — a main road, a railway, a pub garden. It says the same where openings cannot be left open securely: ground-floor bedrooms and any window reachable from a flat roof or balcony, and where outdoor air quality means the ventilation strategy has to limit intake under Part F. When any of those apply, the simplified method cannot honestly be used for the affected rooms. The route is dynamic modelling, with the windows in the model behaving as they will in life — closed at night in the noisy bedroom — and the design made to pass anyway, through shading, acoustic ventilators, secure louvres, mechanical ventilation with a summer bypass, or, last of all, cooling. This is where most Part O effort and money goes on urban sites, and it is why a noise survey often arrives on the desk before the overheating assessment does. ## The dynamic route: what TM59 asks for A TM59 assessment builds a thermal model of the dwelling — every room, its glazing and orientation, the fabric and its thermal mass, the shading, the ventilation openings and their real free areas — and simulates a whole year with TM59's occupancy and internal-gain profiles, in the **CIBSE Design Summer Year** weather file for the 2020s, high emissions, 50th percentile. Windows open in the model when the room passes 22 °C and are fully open at 26 °C; at night they open only where the room is above 23 °C at 11pm and the window is above ground floor and not easily accessible. The home passes if it meets **both** criteria: - **Living rooms, kitchens and bedrooms:** the operative temperature exceeds the adaptive comfort threshold by 1 K or more for no more than **3% of occupied hours** from May to September. - **Bedrooms at night:** the operative temperature between 10pm and 7am exceeds **26 °C** for no more than **1% of annual hours** — 32 hours a year. The bedroom criterion is the one that fails, and it fails on west-facing bedrooms with a single window first. The fixes, in the order an assessor reaches for them: cut or shade the glazing, improve the g-value, add secure night ventilation, use cross-ventilation where the plan allows, add thermal mass, add mechanical ventilation with a boost — and only then cooling, because Requirement O1 makes mechanical cooling the last resort and Approved Document O asks the designer to show Building Control that **all practicable passive means** were used first. Cooling that is installed also has to be carried into the [Part L](/services/sap-calculations/new-builds/) calculation, where it costs energy. CIBSE published a substantially revised **TM59 in July 2026** — a passive-first three-stage method, four criteria and a rewritten bedroom test. Approved Document O still cites the 2017 edition, so for Building Control the 2017 criteria remain the test; [what the 2026 rewrite changes](/news/cibse-tm59-2026-overheating-update/) is worth knowing if you are designing now. ## What Building Control gets For either route: the **compliance checklist** in Appendix B of Approved Document O, completed and signed, showing which route was used and the figures. For the modelling route, the **TM59 report** with the contents the methodology specifies. And the owner must be given non-technical information on how the home is meant to stay cool — which windows to open, what the shading is for — because a passive strategy only works if the people in the house know it exists. ## Wales, Scotland and London **Wales** has its own Part O and Approved Document O, in force since 23 November 2022, with the same two routes but a simplified method organised by single- or dual-aspect dwellings rather than by London postcode. **Scotland** has no Part O; overheating is **Standard 3.28** of the Domestic Technical Handbook, in force since 1 December 2022, again with a simple method and a TM59 route. **London** adds a planning-stage layer on top of Part O: the London Plan's cooling hierarchy expects major schemes to demonstrate overheating performance with TM59 modelling at application stage — so a London scheme often models twice, once for planning and once for Building Control. [Our Part O service](/services/part-o-overheating/) covers all three. ## The bottom line Part O is a drawings problem before it is a modelling problem. If the largest glazed façade faces north or east, the dwelling is cross-ventilated, the site is not in a London high-risk postcode and the bedrooms are quiet enough to sleep with the windows open, the simplified method will usually pass and the assessment is quick. Move any one of those — south or west glass, a single-aspect flat, a main road — and you are into TM59, where the cost of the fix rises the later it is found. The cheapest Part O assessment is the one done on the planning drawings. --- # What is the Future Homes Standard? URL: https://energycount.co.uk/guides/future-homes-standard/ Updated: 2026-09-04 > **Quick answer:** the Future Homes Standard is England's next set of new-build energy regulations — published 24 March 2026 as Approved Document L 2026, and applying to schemes from **24 March 2027**. New homes must emit **at least 75% less carbon** than 2013-standard homes, in practice meaning heat pumps or heat networks, tighter fabric limits and, for most houses, rooftop solar. As of August 2026, compliance at launch is assessed in **SAP 10.3** (the Home Energy Model comes later). ## What it is The Future Homes and Buildings Standard (FHS) is the next generation of Building Regulations energy requirements for England, and the biggest change to new-build standards since [Part L](/guides/building-regulations-part-l/) was last fundamentally rewritten. It requires new homes to produce **at least 75% less carbon** than a home built to 2013 standards — a step far beyond the 30-31% cut delivered by the [Part L 2021 uplift](/guides/sap-10-whats-new/). The aim is homes that are **zero-carbon-ready**: low-carbon heating (in practice, [heat pumps](/guides/heat-pumps/) or heat networks), high fabric standards and on-site renewable generation, with no reliance on fossil fuels. A zero-carbon-ready home isn't zero-carbon on day one — it's designed so it becomes net-zero as the electricity grid decarbonises, needing no retrofit along the way. ## The timeline The final Approved Documents (new editions of **Approved Document L** Volumes 1 and 2, and **Approved Document F** Volume 1) were published on **24 March 2026**, alongside the government's response to the 2023 consultation and Building Circular 01/2026. | Milestone | Date | | --- | --- | | Approved Documents published | 24 March 2026 | | FHS comes into force (most work) | 24 March 2027 | | Deadline to apply under Part L 2021 | 24 March 2027 | | FHS in force for higher-risk buildings | 24 September 2027 | | Transitional projects must have commenced | 24 March 2028 | A **12-month transition period** protects projects already in the pipeline — more on the detail [below](#transitional-arrangements) — after which the FHS applies in full. ## The four big changes ### 1. Low-carbon heating — the effective end of the gas boiler The FHS doesn't "ban" gas boilers by name. Instead the **75% carbon reduction** target is set at a level no fossil-fuel system can meet — so hybrid boilers and hydrogen-ready boilers won't comply either. In practice that means **air source or ground source [heat pumps](/guides/heat-pumps/)**, or connection to a low-carbon heat network, in the vast majority of new homes. This only affects **new homes**. Existing properties are unaffected: you can still install or replace a gas boiler in an existing house. The government estimates FHS homes will save households up to **£830 a year** versus a typical EPC-C property — though, honestly, savings against a *Part L 2021* new build are more marginal, since heat pump electricity still costs roughly four times as much per unit as gas. ### 2. Fabric — the same U-values, tighter airtightness The FHS keeps a whole-building performance approach, so you can trade off between elements. Two things catch people out. First, **the U-values do not tighten**: the limiting values are identical to Part L 2021 (walls 0.26, floors 0.18, roofs 0.16, windows and doors 1.6), and the SAP 10.3 notional dwelling has the same fabric U-values the 2021 notional already had — what tightens is its air permeability, from 5 to 4. Second, **SAP 10.3 and the Home Energy Model share one notional dwelling** — published as Appendix R of SAP 10.3 and, for HEM, as the dwelling notional buildings document — with only minor differences in implementation: HEM sizes the notional heat pump to the dwelling, where SAP fixes its efficiency at a COP of 2.5. The fabric is the same either way: | Element | Part L 2021 notional | FHS notional (SAP 10.3 and HEM) | Limiting value (unchanged) | | --- | --- | --- | --- | | External walls | 0.18 | 0.18 | 0.26 | | Ground floor | 0.13 | 0.13 | 0.18 | | Roof | 0.11 | 0.11 | 0.16 | | Windows | 1.2 | 1.2 | 1.6 | | Doors | 1.0 | 1.0 | 1.6 | | Airtightness | 5.0 | 4.0 | 8.0 | U-values in W/m²K; airtightness in m³/(h·m²) @ 50 Pa. The notional dwelling sets the target you have to beat; the limiting value is the backstop no element may be worse than. See our [U-values guide](/guides/u-values/) for what these mean in practice, or test a wall, roof or floor build-up against these figures in the free [U-value calculator](/tools/u-value-calculator/). One thing that **doesn't** change: junction [thermal bridging](/guides/thermal-bridging/) stays central to the fabric calculation. Calculated Ψ-values (see [ΨMonkey](/tools/psi-calculator/)) remain the best alternative to penal default values under both SAP 10.3 and HEM — and with a tighter air permeability and a heat-pump baseline, well-detailed junctions matter more, not less. ### 3. Mandatory solar PV — a genuine first This is the headline everyone missed in the earlier drafts. A new **functional requirement L3** makes on-site renewable generation a **legal requirement of Building Regulations** — the first time English regs have mandated renewable generation outright, rather than merely assuming it in the notional dwelling. The rule: rooftop PV equivalent to **40% of the dwelling's ground-floor area** (AD L1 para 5.73), or a "reasonable amount" where shading or orientation genuinely constrain it. That 40% *sounds* unchanged from [SAP 10](/guides/sap-10-whats-new/) — but there's a catch. The conversion factor from roof area to installed power has changed from 1/6.5 (about 153 Wp/m²) to **1/4.5 (about 222 Wp/m²)**, reflecting more efficient modern panels. So while the headline number looks the same, the **actual generation required has risen by roughly 45%**. For most detached and semi-detached homes that means a **3–4 kWp system**. **Exemptions** apply for buildings over 18 metres tall, higher-risk buildings, and sites where a minimum output of **720 kWh per year** can't be achieved — for example due to heavy shading or awkward roof geometry. See our [solar PV guide](/guides/solar-pv/) for how it earns its keep in a compliance calculation. ### 4. Ventilation and airtightness — Part F tightens too The much tighter airtightness targets mean **mechanical ventilation becomes effectively unavoidable** in most FHS homes, whether decentralised mechanical extract ([dMEV](/guides/mvhr/)) or MVHR for the heat-recovery benefit. The updated Approved Document F also changes how systems are signed off: - All new ventilation systems must be **commissioned by a competent person scheme member**. - **Powered flow hoods are now mandatory** for commissioning; rotating vane anemometers are prohibited. Poorly commissioned ventilation has been a persistent problem in airtight new builds, and these changes are a direct response. They sit alongside completion-stage [air tightness testing](/services/air-tightness-testing/), which becomes more important than ever as targets drop. ## The notional dwelling: two routes to the target The published documents offer **two notional dwelling options**, both delivering the same carbon target with a different balance of airtightness and ventilation: | Specification | Option 1 (MVHR) | Option 2 (Natural ventilation) | | --- | --- | --- | | Airtightness | Tighter (~4 m³/h·m²) | Looser (~5 m³/h·m²) | | Ventilation | dMEV / mechanical | Natural ventilation | | Waste water heat recovery | Required ([WWHRS](/guides/waste-water-heat-recovery/)) | Not required | | Solar PV | Required (L3) | Required (L3) | | Low-carbon heating | Required | Required | ## How compliance is assessed: SAP 10.3 now, HEM later Compliance is demonstrated the familiar way — showing your dwelling performs at least as well as a **notional building** of the same size and shape. Approved Document L 2026 retains the three [Part L 2021 metrics](/guides/der-ter/): primary energy rate (DPER), carbon emissions rate (DER) and [fabric energy efficiency](/guides/fabric-energy-efficiency/) (DFEE). No simplification — compliance stays multi-dimensional. At launch, assessment is via **SAP 10.3**, an updated version of the familiar [SAP methodology](/services/sap-calculations/). The government's new **Home Energy Model (HEM)** — a complete replacement for SAP that models performance at half-hourly intervals — was expected to follow around three months after publication, but was **delayed again on 8 June 2026**. As things stand, **SAP 10.3 is the sole approved methodology**, with HEM expected in the coming months, followed by a dual-running period before it eventually replaces SAP entirely. HEM is a bigger shift than the version number suggests: it demands far more data than SAP (early testing suggests a house type takes around 1h40 in HEM versus roughly 20 minutes in SAP), with punitive defaults where data is missing, and it will be delivered through a single central calculation service rather than competing third-party engines. We're tracking every software release closely. ## What it costs The government's impact assessment puts the extra build cost at roughly **£4,350 per dwelling** (weighted average, 2025 prices) — or in the region of **3–8% per home** — driven mainly by the heat pump, solar PV, extra insulation and mechanical ventilation. That's offset by lower running costs and no gas standing charge, and the premium is expected to narrow as heat pump and PV supply chains scale up. Expect a **surge in demand** for both as the deadline approaches, so procurement planning matters. ## Transitional arrangements The 12-month transition runs from **24 March 2027 to 24 March 2028**, and it's stricter than previous uplifts: - Projects with an application submitted **before 24 March 2027** can build to Part L 2021 — **if work commences before 24 March 2028**. - "Commence" includes drainage and foundation work, not just superstructure. - Arrangements operate on an **individual-building basis**, not site-wide, so different plots on the same site can fall under different regs. - Older 2013 and 2021 transitional provisions — which still let some large sites build to 2010 standards — have been **revoked**. Any uncommenced plots relying on them must now meet the FHS. ## What to do now Projects gaining planning consent from here on will most likely be built under the FHS — so design for it now: heat pump heating, strong fabric, mechanical ventilation planned from the start, and [solar PV](/guides/solar-pv/) sized to L3. Get the [thermal bridging](/guides/thermal-bridging/) detailed properly while the drawings are live, and don't fix a specification for 2027 starts before you've stress-tested it against the numbers. We're tracking the secondary legislation and software releases closely — [talk to us](/contact/) before you lock in a spec, and we'll tell you where the risks are. --- # What is DER/TER? URL: https://energycount.co.uk/guides/der-ter/ Updated: 2026-08-31 > **Quick answer:** DER is the Dwelling Emission Rate — your design's calculated CO₂ emissions in kgCO₂/m² per year. TER is the Target Emission Rate, calculated for a notional dwelling of the same size and shape. **Pass = DER ≤ TER.** Both come out of the SAP calculation, and under Part L 2021 they sit alongside a primary-energy test (DPER ≤ TPER) and a fabric test (DFEE ≤ TFEE). ## The carbon pass/fail The **Dwelling Emission Rate (DER)** and **Target Emission Rate (TER)** are the primary CO₂ figures measured by [SAP calculations](/services/sap-calculations/), expressed in kgCO₂/m² per year. The design-stage SAP sets the target (TER); the proposed dwelling's actual rate (DER) must be equal to or lower than it to pass Part L. The TER is derived from a **notional dwelling** of the same type and size as yours. Under [SAP 10](/guides/sap-10-whats-new/) the notional dwelling has a demanding specification — including an assumed PV array — which is why the TER is much harder to beat than under older versions of SAP. A parallel primary energy target (DPER vs TPER) was also added in Part L 2021. ## What moves the DER Plenty: orientation, [fuel choice](/guides/fuel-choice-in-sap/), [u-values](/guides/u-values/), [air tightness](/services/air-tightness-testing/), [thermal bridging](/guides/thermal-bridging/), heating system efficiency and renewables. Energy assessors use the DER/TER gap to show the design team exactly where a dwelling is underperforming — and the cheapest places to claw it back. The fabric side is the part you can test yourself before an assessor runs the full SAP: model element [U-values in the free U-value calculator](/tools/u-value-calculator/) and junction [Ψ-values in the free thermal-bridging calculator](/tools/psi-calculator/) to see how much headroom your specification gives the DER — often the junctions are the cheapest place to find it. Note that CO₂ isn't the only criterion: [fabric energy efficiency](/guides/fabric-energy-efficiency/), limiting u-values, services and air tightness standards must all be met too. But miss the DER target and the dwelling fails regardless. --- # What is Fabric Energy Efficiency (DFEE/TFEE)? URL: https://energycount.co.uk/guides/fabric-energy-efficiency/ Updated: 2026-08-31 > **Quick answer:** Fabric Energy Efficiency (FEE) is SAP's fabric-only heat demand metric, in kWh/m² per year. **DFEE** (your dwelling's figure) must not exceed **TFEE** (the target — a notional dwelling's fabric demand plus 15%). Renewables can't rescue it: only insulation, air tightness and thermal bridging move the number. As of August 2026 it remains a compliance metric under Part L 2021; the Future Homes Standard supersedes it for schemes from 24 March 2027. ## What does DFEE stand for? DFEE stands for **Dwelling Fabric Energy Efficiency** — your design's fabric-only heat demand in kWh/m² per year, before any credit for renewables or heating. To pass Part L your DFEE must be equal to or lower than your **TFEE** (Target Fabric Energy Efficiency). ## Why a fabric target exists Before April 2014, new homes in England & Wales were assessed in Part L against a carbon target only ([DER/TER](/guides/der-ter/)). That skewed designs in odd ways — you could build with inefficient fabric and rescue the CO₂ number with renewables or low-carbon heating. Sensible engineering (and the [energy hierarchy](/guides/energy-hierarchy/)) says reduce heat losses first, then add renewables. So Fabric Energy Efficiency (FEE) was added to Part L in the 2013 edition (effective 6 April 2014). In SAP it appears as **DFEE/TFEE** — Dwelling vs Target Fabric Energy Efficiency, measured in **kWh/m² per year**. The dwelling's DFEE must be equal to or lower than the TFEE of the notional dwelling. ## What drives it Fabric energy efficiency is exactly what it sounds like: the heat-loss performance of the building fabric itself — - [u-values](/guides/u-values/) of walls, floors, roofs and openings - [air tightness](/services/air-tightness-testing/) - [thermal bridging](/guides/thermal-bridging/) at junctions Renewables can't help you here — that's the point. If your DFEE is marginal, the fixes are fabric fixes, and calculated junction Ψ-values (try [ΨMonkey](/tools/psi-calculator/)) are often the cheapest one available, since they improve the number without changing anything on site. ## How the TFEE target is actually set Your target isn't a fixed national number — it's built from **your** dwelling. SAP takes a **notional dwelling** of identical size, shape and orientation, gives it a standard reference fabric specification, and calculates its fabric energy demand. Then, following the 2013 consultation, it adds a **15% flexibility allowance** so designers aren't pinned to the exact notional detail: **TFEE = notional dwelling fabric energy demand + 15%.** Because the notional building is the same shape as yours, the target automatically reflects how compact your design is. A blocky mid-terrace has far less exposed surface per m² of floor than a sprawling detached bungalow, so its TFEE lands lower — the more exposed fabric a form has, the more heat it can lose, and the target moves with it. This is why two dwellings on the same site can have very different TFEE figures, and why "just copy the plot next door's spec" doesn't always work. ### A worked example Say the notional version of your dwelling comes out at **40 kWh/m²/yr** of fabric demand. Add the 15% allowance and your **TFEE is about 46 kWh/m²/yr**. Your job is to design fabric whose **DFEE** lands at or below that 46. Get your walls, roof, floor, glazing, air tightness and junctions modelled and your DFEE comes in at, say, 44 — you pass the fabric test with 2 kWh/m²/yr to spare. Come in at 49 and you've failed it, no matter how much PV or how efficient a heat pump you bolt on afterwards. (The 40 and 46 here are illustrative — real figures depend on dwelling type, size and compactness, so always work from your own SAP model rather than a rule of thumb.) ## How FEE fits with the other SAP targets Fabric energy efficiency is **one of several tests** a new-build SAP has to pass at once, not the whole story. Under [SAP 10 / Part L 2021](/guides/sap-10-whats-new/) a new dwelling must satisfy: - **Primary energy** — DPER must beat TPER (the headline metric in Part L 2021). - **Carbon** — [DER must beat TER](/guides/der-ter/). - **Fabric energy efficiency** — DFEE must beat TFEE (this page). - **Limiting standards** — individual u-values, air tightness and fixed building services must all sit within their backstops. Miss any one of them and the dwelling fails. FEE is the one that can't be bought back with kit — it's a deliberate floor under the fabric, so a home stays efficient even as the grid and its heating system change around it. ## DFEE looking marginal? Where to claw it back Because FEE is fabric-only, the levers are all fabric levers — and some are far cheaper than others: - **Calculated junction Ψ-values.** Usually the cheapest win. Poorly-detailed junctions can be 20–30% of fabric heat loss, and swapping punitive SAP defaults for [calculated Ψ-values](/tools/psi-calculator/) improves the number without changing a thing on site. - **Air tightness.** Tightening the target the build can actually achieve (and prove on test) directly cuts fabric demand. - **U-values.** Better walls, roof and — often overlooked — [glazing](/guides/u-values/) and its frames. Marginal upgrades to insulation thickness or a better window spec move the DFEE. - **Reduce needless glazing / sort orientation.** Oversized north-facing glazing loses heat with little solar gain in return; the fabric metric notices. An assessor reads the DFEE/TFEE gap to show you exactly which of these is the cheapest route back to a pass — often it's the junctions, not another 25mm of insulation everywhere. ## What the Future Homes Standard changes Worth knowing where this is heading. Under **[Approved Document L 2026](/news/future-homes-standard-adl-2026/)** — the Future Homes Standard, published 24 March 2026 and **in force 24 March 2027** — the separate DFEE/TFEE pass/fail looks set to be **superseded** by a whole-building approach built around carbon and primary energy (targeting roughly a 75% cut in emissions versus 2013), backed by tighter limiting fabric U-values and a new renewables requirement. That doesn't mean fabric stops mattering — the opposite. As walls, roofs and floors get tighter, [thermal bridging](/guides/thermal-bridging/) becomes a bigger slice of what's left, and fabric performance re-emerges as one of the four headline metrics on the [reformed EPC](/news/reformed-epcs-four-metrics-home-energy-model/). And until 24 March 2027, **DFEE/TFEE still applies** to your Part L 2021 submissions, so it's very much a live test today. ## The bottom line Fabric energy efficiency is the test you can't cheat with renewables — get the [u-values](/guides/u-values/) right, tighten the [air test](/services/air-tightness-testing/), and nail the [junctions](/guides/thermal-bridging/). If a DFEE is coming up marginal, calculated Ψ-values are frequently the cheapest single fix: model yours free with [ΨMonkey](/tools/psi-calculator/), then hand the numbers to your [SAP assessor](/services/sap-calculations/) — no subscription, no sign-up. --- # What is a U-value? URL: https://energycount.co.uk/guides/u-values/ Updated: 2026-09-03 > **Quick answer:** a U-value measures how fast heat passes through a building element, in watts per square metre per degree (W/m²K) — so **lower is better**. New-build walls in England must not exceed 0.26 W/m²K under Part L 2021, and typically need to reach about 0.18 to pass the overall SAP. Those limits do **not** change under the Future Homes Standard in 2027. ## The definition A U-value (thermal transmittance) measures how readily heat passes through a building element — wall, floor, roof, window or door — in **W/m²K**: watts of heat lost per square metre, per degree of temperature difference between inside and out. **Lower is better.** A solid Victorian brick wall might be around 2.0; a modern insulated cavity wall 0.18; a Passivhaus wall 0.10–0.15. Put another way: a 1 m² wall with a U-value of 0.2 W/m²K, with 20°C inside and 0°C outside, loses 0.2 × 20 = **4 watts** through that square metre. Scale that across the whole envelope and you can see why the figure matters so much for both energy bills and the [SAP calculation](/services/sap-calculations/) that proves compliance. If you have come from an American source, **U-factor** is the same thing in Btu/(h·ft²·°F); multiply a U-factor by 5.68 to get W/m²K, or a U-value by 0.176 to go the other way. ## Which U-value do I need? This is the question most people arrive with, and the answer depends on which of three situations you are in. All figures W/m²K, from Approved Document L Volume 1, 2021 edition. | Element | New dwelling — notional (the target) | New dwelling — limiting (never exceed) | New element in an existing dwelling | Retained element — upgrade if worse than → to | | --- | --- | --- | --- | --- | | External wall | 0.18 | 0.26 | 0.18 | 0.70 → 0.55 (cavity fill) / 0.30 (internal or external insulation) | | Floor | 0.13 | 0.18 | 0.18 | 0.70 → 0.25 | | Roof | 0.11 | 0.16 | 0.15 | 0.35 → 0.16 | | Party wall | 0 | 0.20 | — | — | | Windows | 1.2 | 1.6 | 1.4 (or Window Energy Rating band B) | — | | Doors | 1.0 | 1.6 | 1.4 (or Doorset Energy Rating band B/C) | — | | Rooflights | 1.7 | 2.2 | 2.2 | — | Three things to take from the table. **New build:** the limiting column is a backstop, not a target — a dwelling built to 0.26 walls passes that row and fails the SAP by a distance, because the notional dwelling it is measured against has walls at 0.18 and solar panels on the roof. Build between the two columns and the shortfall has to be made up elsewhere in the calculation. **Existing dwellings:** the "new element" column is what an extension wall, a new roof or a replacement window has to hit, and it is tighter than the new-build backstop. **Renovation:** a retained element worse than the threshold has to be improved to the second figure where that is technically and functionally feasible and pays back within 15 years — the clause that keeps solid-wall houses insurable and barn conversions possible. The [Part L guide](/guides/building-regulations-part-l/) explains which edition applies to your project; [U-Monkey](/tools/u-value-calculator/) checks a build-up against every column live. ## Area-weighting — and the window trap The limiting values for walls, floors and roofs apply to the **area-weighted average** of all elements of that type: multiply each section's U-value by its area, add them up, divide by the total area. A short run of weaker wall can be carried by better wall elsewhere, and that same arithmetic is one of the two routes to compliance for an [over-glazed extension](/services/sap-calculations/extensions/). The exception catches people every week. In an existing dwelling, **windows, doors, roof windows and rooflights are excluded from area-weighting** — every single one has to meet 1.4 on its own. You cannot average a poor window against a good one. Where a building's character genuinely requires the original windows, the Approved Document accepts a centre-pane U-value of 1.2 or better, or single glazing with low-emissivity secondary glazing behind it. ## How a U-value is actually calculated U-values are calculated from the **build-up** of the element — not measured on a wall. The calculation, to **BS EN ISO 6946**, adds up the thermal resistance of every layer: 1. **Each material layer** contributes its thickness (m) divided by its thermal conductivity λ (W/m·K) — its *R-value*. The lower the λ, the better the insulator. 2. **Surface resistances** — the still-air films on the inside and outside faces. Inside: 0.13 m²K/W for a wall, 0.10 for a roof (heat flowing up), 0.17 for a floor (heat flowing down). Outside: 0.04 for all of them. 3. **Corrections** — for repeating thermal bridges like timber studs or mortar joints, air gaps between layers, and mechanical fixings that pierce the insulation. The total resistance RT = Rsi + R1 + R2 + … + Rse, and the U-value is simply **U = 1 / RT**. Ground floors use **BS EN ISO 13370** instead, because heat loss through the ground depends on the floor's perimeter-to-area ratio — the same slab gets a different U-value in a different floor plan. And the whole thing follows the conventions of **BR 443** (third edition, 2019) so that one assessor's software agrees with another's: default bridging fractions, air-gap corrections, and — critically — which conductivity values you are allowed to use. That is exactly the method our free [**U-Monkey calculator**](/tools/u-value-calculator/) uses — build up your element from real UK products and it computes the U-value, the [Part L](/guides/building-regulations-part-l/) and [Future Homes Standard](/guides/future-homes-standard/) checks, and a condensation screening, with the PDF report free. [How to use U-Monkey](/tools/u-value-calculator/how-to-use/) walks through a build-up layer by layer, bridging fractions and cavities included. ### A worked example Take a modern insulated cavity wall, outside → inside: | Layer | Thickness (mm) | λ (W/m·K) | R (m²K/W) | | --- | --- | --- | --- | | External surface (Rse) | — | — | 0.04 | | Brick outer leaf | 102.5 | 0.77 | 0.13 | | Full-fill mineral wool | 100 | 0.035 | 2.86 | | Aircrete block inner leaf | 100 | 0.11 | 0.91 | | Plasterboard | 12.5 | 0.25 | 0.05 | | Internal surface (Rsi) | — | — | 0.13 | Total resistance RT = 0.04 + 0.13 + 2.86 + 0.91 + 0.05 + 0.13 = **4.12**, so U = 1 / 4.12 ≈ **0.24 W/m²K** — before corrections for mortar joints and wall ties, which push it a touch higher; the [full-fill cavity wall page](/tools/u-value-calculator/cavity-wall-full-fill/) shows the real-world figures. Change the insulation to 150 mm and U drops to roughly 0.18; switch to PIR (λ 0.022) and it is better still. That sensitivity is why the build-up — not the wall "type" — is what your SAP assessor needs. Hand-summing like this only works for a homogeneous element. Anything with timber studs, wall ties, metal fixings or a ground floor needs the bridging and correction methods — which is what the software is for. ### R-value vs U-value They are often confused. **R-value** is a property of a single layer or assembly (m²K/W) — resistance, higher is better. **U-value** is the overall element performance including surface films (W/m²K) — transmittance, lower is better. You cannot sensibly compare one with the other; Part L and SAP work in U-values. ## Materials do not have U-values — they have conductivities People search for "the U-value of wood" or "the U-value of steel". A material has a **thermal conductivity, λ**, in W/m·K; it only acquires a U-value once it is a layer of a certain thickness in an element with surfaces. The conductivities that matter, from the BR 443 conventions and the manufacturers' declared values: | Material | λ (W/m·K) | Note | | --- | --- | --- | | Brickwork, outer leaf | 0.77 | BR 443 default (inner leaf 0.56) | | Softwood timber | 0.13 | BR 443 default (hardwood 0.18) | | Mild steel | 50 | BR 443 default — a stud or a lintel is a thermal bridge, not an insulator | | Reinforced concrete | 2.30 | BR 443 default | | Plasterboard | 0.21–0.25 | BR 443 default, by density | | Unventilated cavity, ≥25 mm | R = 0.18 m²K/W | A resistance, not a conductivity; it does not improve with a wider cavity | | Dense concrete block | ~1.1–1.3 | Typical — use the manufacturer's declared value | | Aircrete block | ~0.11–0.19 | Typical — use the manufacturer's declared value | | Mineral wool | ~0.032–0.044 | Typical — use the declared value | | EPS | ~0.030–0.038 | Typical — use the declared value | | PIR | ~0.022 | Typical — use the declared value | The distinction in the right-hand column matters. BR 443 tabulates defaults for masonry, timber and metals but **not for blocks or insulation** — for those it requires the manufacturer's *declared* λ, which is a certified figure a little more pessimistic than the lab value. A calculation built on a generic insulation figure instead of the declared one is a common reason for a U-value being rejected, and why the same build-up can give different answers in different software. U-Monkey uses declared values throughout. ## Windows: whole-window, not centre-pane Part L uses the **whole-window U-value** — glass, frame and spacer together — not the centre-pane figure a glazing brochure leads with. A unit with a centre-pane value of 1.0 can sit in a window whose whole-window value is 1.4 to 1.6, so the glass-only figure is not a compliance figure. In an existing dwelling the Approved Document accepts a **Window Energy Rating** as an alternative to a U-value — band B or better for windows — which can reward a window that admits useful solar gain in a way the U-value alone cannot. ## Passivhaus U-values Passivhaus does not actually set a maximum U-value for walls, roofs or floors. The standard is performance-based — a **space heating demand of 15 kWh/m² a year** or less, an **airtightness of 0.6 air changes per hour** at 50 Pa, and a primary energy limit — and the fabric is whatever it takes to get there, which in the UK's cool-temperate climate typically means opaque elements at **0.10 to 0.15 W/m²K**. Windows are certified as components: a whole-window U-value of **0.80** or better and **0.85 installed**, with glazing at 0.70 or better. That is about half the Part L limit for a new dwelling, and it is where triple glazing stops being optional. ## Measuring a U-value in an existing wall When the build-up is unknown — a rendered wall that might or might not have a cavity, a stone wall of uncertain thickness — the U-value can be **measured in situ** with a heat flux plate to **BS ISO 9869-1**. A sensor on the inside face and temperature probes inside and out log for a minimum of **72 hours** in the heating season, and the test ends only when the result has stopped moving — within 5% over the last 24 hours. Heavy masonry walls often need considerably longer; lightweight walls are analysed on night-time data only, to exclude the sun. It is the honest answer to "what is my wall actually doing?" for a retrofit design or a suspected workmanship problem — but BRE's guidance is that it is not suitable for producing an individual dwelling's EPC. ## Typical U-values — a reality check | Element | Typical U-value (W/m²K) | | --- | --- | | Solid brick wall (uninsulated, pre-1900) | ~2.0–2.2 | | Uninsulated cavity wall (1930s–60s) | ~1.5–1.6 | | Insulated cavity wall (modern, full-fill) | ~0.28–0.30 | | Timber frame wall | ~0.20–0.24 | | Loft insulation at 270 mm | ~0.11–0.13 | | Rafter-level pitched roof | ~0.15–0.18 | | Insulated concrete ground floor | ~0.13–0.18 | | Suspended timber floor, insulated | ~0.15–0.22 | | Single glazing | ~5.8 | | Double glazing (low-e, argon) | ~1.2–1.6 | | Triple glazing | ~0.8–1.0 | There is a page of typical values and editable build-ups for the most common constructions — [cavity walls](/tools/u-value-calculator/cavity-wall-full-fill/), [solid walls](/tools/u-value-calculator/solid-brick-wall-internal-insulation/) (including the [one-and-a-half-brick, 317.5mm solid wall](/tools/u-value-calculator/one-and-a-half-brick-wall/)), [timber-frame walls](/tools/u-value-calculator/timber-frame-wall/), [pitched roofs](/tools/u-value-calculator/pitched-roof-rafter-insulation/), [flat roofs](/tools/u-value-calculator/warm-flat-roof/) (including [how much flat-roof insulation you need](/tools/u-value-calculator/flat-roof-insulation-thickness/)), [loft insulation](/tools/u-value-calculator/loft-insulation-270mm/), [concrete ground floors](/tools/u-value-calculator/insulated-concrete-floor/), [suspended timber floors](/tools/u-value-calculator/suspended-timber-floor-insulation/) and [beam & block floors](/tools/u-value-calculator/beam-and-block-floor/). ## How to improve a U-value Almost always in this order: 1. **Add insulation** — the single biggest lever. Where it goes (cavity fill, external wall insulation, internal wall insulation, loft, floor overlay) depends on the element and the building. 2. **Insulate the whole element, not part of it** — a thermal bridge at the edge undoes good work elsewhere (see below). 3. **Upgrade the windows** — low-e glass, argon fill and warm-edge spacers take a typical double-glazed unit from ~1.6 to ~1.2. 4. **Don't chase the last 0.02** — beyond ~0.15, each extra millimetre of insulation buys very little; the [energy hierarchy](/guides/energy-hierarchy/) and [fabric energy efficiency](/guides/fabric-energy-efficiency/) guides put this in perspective. ## What changes in 2027 — and what does not Approved Document L 2026, the Future Homes Standard, takes effect on **24 March 2027**. The limiting U-values **do not change**: walls 0.26, floors 0.18, roofs 0.16, windows and doors 1.6, rooflights 2.2 — the same numbers, renumbered into new tables — and the notional dwelling's fabric values are unchanged too. What tightens is the notional dwelling's **air permeability**, the switch to a **heat-pump** baseline, and a new legal requirement for **on-site renewables**. If you arrived here expecting a new set of U-value limits for 2027, there isn't one; the fabric you design to Part L 2021 is the fabric the Future Homes Standard expects. ## U-values aren't the whole story An element's U-value covers its flat area — but heat also escapes where elements meet. Those junction losses are measured separately as Ψ-values, and at modern U-value levels they can be 20–30% of total fabric heat loss. See [thermal bridging explained](/guides/thermal-bridging/), calculate junction values with the free [psi value calculator](/tools/psi-calculator/), or build to [Accredited and Recognised Construction Details](/guides/accredited-construction-details/) and use their published values. U-values also feed everything downstream: [SAP](/services/sap-calculations/) and [SBEM](/services/sbem-calculations/) calculations, [energy statements](/services/energy-statements/), [Part O](/services/part-o-overheating/) overheating checks (better fabric often means more careful glazing design) and [Part G](/services/part-g-water-calculations/) hot-water demand. Get the fabric right and the rest of the compliance picture gets easier. --- # Accredited Construction Details (ACDs) and Recognised Construction Details (RCDs) explained URL: https://energycount.co.uk/guides/accredited-construction-details/ Updated: 2026-09-03 ## What ACDs were for Accredited Construction Details are a government-published set of junction specifications — wall-to-floor, eaves, openings and so on — each with a pre-approved Ψ-value. Build exactly to the published detail, and your SAP assessor could apply that improved value instead of the punitive default. They were the easiest way to soften [thermal bridging](/guides/thermal-bridging/) losses without commissioning calculations. ## Why SAP 10 removed them The ACD set aged badly: the details no longer reflect modern constructions, and there were long-standing concerns about the accuracy of the published values. [SAP 10](/guides/sap-10-whats-new/) removed the option to use them entirely. ## Recognised Construction Details (RCDs) — the current scheme Recognised Construction Details are what replaced the ACD shortcut for masonry. They are a **free database of independently assessed junction details** — aggregate block and aircrete, at standard cavity widths — each published with a **psi value and an f-value** (the condensation-risk factor), and certified for use in demonstrating Part L compliance. The portal is run by Building Alliance CIC; the junctions were commissioned by the Concrete Block Association and the Aircrete Products Association and modelled independently. The deal is the same as it was with ACDs: build the junction *exactly* as drawn and the assessor can enter the RCD psi value in SAP instead of the default. Deviate — a different cavity closer, insulation stopped short, a lintel the detail didn't assume — and the value no longer applies. They cover the standard junction set for masonry housing; they do not cover timber frame, SIPs, steel frame or anything non-standard, which is where a calculated value comes in. LABC's **Registered Construction Details** are the other scheme you will meet, aimed at smaller builders. Both are valid sources where the match is exact. ## Your options now 1. **Scheme details — RCDs, LABC Registered Details, manufacturer schemes** — independently assessed junctions with published Ψ-values, free or near-free, valid only if your construction matches the drawing exactly. Masonry is well covered; other systems mostly are not. 2. **Calculated Ψ-values to BS EN ISO 10211** — bespoke values for your actual details. Almost always gives the best result, and it's what our free [ΨMonkey psi calculator](/tools/psi-calculator/) produces, with Building Control-ready reports at £25 a junction. 3. **Default values** — always available, always punitive. Avoid if the SAP is anywhere near marginal. As-built [EPCs](/services/sap-calculations/epc/) need the junction evidence documented, so decide your thermal bridging strategy at design stage, not at sign-off. --- # What is the Energy Hierarchy? URL: https://energycount.co.uk/guides/energy-hierarchy/ Updated: 2026-06-11 ## The principle The energy hierarchy ranks the ways to cut a building's carbon footprint, in order of preference: 1. **Reduce energy demand** — fabric first: insulation ([u-values](/guides/u-values/)), [air tightness](/services/air-tightness-testing/), minimised [thermal bridging](/guides/thermal-bridging/), good form and orientation. 2. **Use energy efficiently** — efficient heating systems and controls, [MVHR](/guides/mvhr/), LED lighting, [waste water heat recovery](/guides/waste-water-heat-recovery/). 3. **Supply from low-carbon and renewable sources** — [heat pumps](/guides/heat-pumps/), [solar PV](/guides/solar-pv/), [solar hot water](/guides/solar-hot-water/). London plans phrase it as "be lean, be clean, be green" — and many Local Planning Authorities structure their [energy statement](/services/energy-statements/) requirements around exactly this logic, expecting demand reduction to be demonstrated before renewables are counted. ## Why the order matters A kilowatt-hour you never need is cheaper than one you generate. Fabric measures are permanent, maintenance-free and invisible to occupants; renewables degrade, need replacing, and underperform on poorly designed buildings. Part L embeds the same thinking through the [fabric energy efficiency target](/guides/fabric-energy-efficiency/), which renewables can't satisfy. It's also why we push [calculated junction Ψ-values](/tools/psi-calculator/) so hard: they're a step-1 improvement that costs nothing on site. --- # Why is Fuel Choice Important in SAP? URL: https://energycount.co.uk/guides/fuel-choice-in-sap/ Updated: 2026-06-11 ## Every fuel carries a carbon factor SAP converts every kWh your dwelling uses into CO₂ and primary energy using fuel-specific factors. Your target ([TER](/guides/der-ter/)) is set by a notional dwelling using mains gas — so fuels with worse factors than gas start at a disadvantage that must be clawed back elsewhere. ## The SAP 10 shake-up Under SAP 2012, grid electricity carried a carbon factor 2.4× that of mains gas — making all-electric new builds notoriously hard to pass. [SAP 10](/guides/sap-10-whats-new/) cut electricity's factor from 0.519 to 0.233 kgCO₂/kWh, barely above gas (0.210), reflecting today's cleaner grid. Direct electric heating is now viable in the calculation — and a [heat pump](/guides/heat-pumps/), delivering 3+ units of heat per unit of electricity, comfortably beats gas on carbon. ## Practical implications **Mains gas** remains the baseline the targets assume — but with the [Future Homes Standard](/guides/future-homes-standard/) phasing fossil-fuel heating out of new builds, it's a shrinking option. **Heat pumps** are now usually the strongest choice in SAP terms. **Direct electric** (panel heaters, electric boilers) passes more easily than before but high running costs still show in the calculation. **LPG and oil** carry worse economics and carbon, and typically need fabric or renewable compensation. Choosing fuel early — before the [design-stage SAP](/services/sap-calculations/) — avoids expensive redesign. If you're undecided, we can model the options side by side. [Ask us](/contact/). --- # What is a Predicted Energy Assessment (PEA)? URL: https://energycount.co.uk/guides/predicted-energy-assessment/ Updated: 2026-06-11 ## The off-plan EPC A Predicted Energy Assessment (PEA) shows the predicted energy rating of a dwelling that hasn't been built yet. It's produced from the design-stage [SAP calculation](/services/sap-calculations/) and is required when a new dwelling is marketed for sale or rent off-plan — viewers are entitled to see an energy rating even though the final [EPC](/services/sap-calculations/epc/) can't yet exist. ## PEA vs EPC The PEA presents the same A–G energy band as an EPC but is based on the proposed specification, carries no certificate number, and isn't lodged on the national register. Once the dwelling is complete, the as-built SAP calculation produces the official EPC, which supersedes the PEA — and which Building Control needs before sign-off. If we're already doing your design-stage SAP, a PEA is a quick add-on — just ask when sales or lettings marketing is planned. [Get a quote](/contact/) or call 01202 623236. --- # Renewable Technologies: An Overview URL: https://energycount.co.uk/guides/renewable-technologies/ Updated: 2026-06-11 ## The headliners **[Solar PV](/guides/solar-pv/)** — generates electricity, directly offsets the dwelling's energy and carbon figures, and is assumed in the [SAP 10 notional dwelling](/guides/sap-10-whats-new/). For most new builds it's the simplest route to a pass. **[Heat pumps](/guides/heat-pumps/)** — [air source](/guides/air-source-heat-pumps/) or [ground source](/guides/ground-source-heat-pumps/), delivering 3–4 units of heat per unit of electricity. The default heating choice under the [Future Homes Standard](/guides/future-homes-standard/). **[Solar hot water](/guides/solar-hot-water/)** — solar thermal panels feeding the cylinder; a useful contributor, though PV has largely displaced it on cost. ## The supporting cast **[MVHR](/guides/mvhr/)** — mechanical ventilation with heat recovery; shines in airtight dwellings. **[Waste water heat recovery](/guides/waste-water-heat-recovery/)** — recovers shower drain heat, cheap, and assumed in the SAP 10 notional dwelling. **[Flue gas heat recovery](/guides/flue-gas-heat-recovery/)** and **[weather compensation](/guides/weather-compensation/)** — boiler-side efficiency improvements worth real SAP points for small money. ## Choosing for your project The right mix depends on the planning condition wording, the fabric, the fuel and the budget — and the [energy hierarchy](/guides/energy-hierarchy/) says fix fabric first. We model options side by side as part of [SAP work](/services/sap-calculations/) and [energy statements](/services/energy-statements/), so you buy the technology that earns its keep. [Ask us](/contact/). --- # Solar PV (Photovoltaic Panels) URL: https://energycount.co.uk/guides/solar-pv/ Updated: 2026-06-11 ## Why PV dominates new-build compliance Solar photovoltaic panels generate electricity from daylight, directly reducing a dwelling's modelled energy demand and CO₂ emissions. The [SAP 10 notional dwelling](/guides/sap-10-whats-new/) includes an assumed PV array — roughly **4kW for an average house** — so a dwelling without PV starts behind its target and must make the difference up elsewhere. In practice, PV (or a [heat pump](/guides/heat-pumps/)) is how most SAP 10 passes are achieved. PV is also the most common answer to [planning conditions](/services/energy-statements/) requiring a percentage CO₂ or energy demand reduction from renewables. ## What affects the SAP contribution Array size (kWp), orientation and pitch (south-facing ~35° is ideal; east/west loses ~15–20%), and overshading. SAP 10 allows MCS overshading data instead of defaults, and now recognises **battery storage** and **PV diverters** (which dump surplus generation into the hot water cylinder). For flats, only dwellings directly connected to an array get the benefit — landlord-supply arrangements no longer count for everyone. ## Practical notes Panels are typically roof-mounted on-roof or integrated (in-roof trays look cleaner on new builds and avoid raised fixings). No moving parts, 25-year+ panel warranties, minimal maintenance. Tell us early if PV is in the design — sizing it precisely against the [SAP calculation](/services/sap-calculations/) avoids paying for panels you don't need. --- # Heat Pumps: An Introduction URL: https://energycount.co.uk/guides/heat-pumps/ Updated: 2026-06-11 ## How they work A heat pump moves heat rather than generating it: refrigerant absorbs low-grade heat from outside air or the ground, a compressor raises its temperature, and a heat exchanger delivers it to your heating and hot water. The efficiency measure is the **SCOP** (seasonal coefficient of performance) — typically 3–4, meaning 3–4 kWh of heat per kWh of electricity. No flue, no fossil fuel, no combustion. ## In the SAP calculation With [SAP 10's electricity carbon factor](/guides/sap-10-whats-new/) down at 0.233 kgCO₂/kWh, a heat pump at SCOP 3+ beats a gas boiler on carbon by a wide margin — usually the single biggest lever available for a [SAP pass](/services/sap-calculations/). And with the [Future Homes Standard](/guides/future-homes-standard/) removing fossil-fuel heating from new homes from 2027, heat pumps are becoming the default rather than the alternative. They suit low-temperature systems best: underfloor heating or generously sized radiators, in a well-insulated, airtight dwelling — which new builds are by definition. ## Air source or ground source? **[ASHP](/guides/air-source-heat-pumps/)** — an external unit extracting heat from air. Cheaper, simpler, fits almost any plot; SCOP slightly lower and drops in the coldest weather. **[GSHP](/guides/ground-source-heat-pumps/)** — extracts heat from the ground via buried loops or boreholes. Higher SCOP and steadier year-round, but significantly higher install cost and needs land or drilling. Best on larger plots, larger houses, or shared-loop developments. We model both options in SAP as standard — [ask us](/contact/) which earns its cost on your project. --- # ASHP — air source heat pumps explained URL: https://energycount.co.uk/guides/air-source-heat-pumps/ Updated: 2026-09-03 > **Quick answer:** an air source heat pump (**ASHP**) heats a home by extracting heat from outside air — working even below freezing — and upgrading it with a compressor. A modern unit is rated at **3.5–4.5 units of heat per unit of electricity** in the lab and returns a median of about **2.8 in monitored UK homes**, against roughly 0.9 for a gas boiler's best. Grant of **£7,500** (£9,000 off-grid from oil or LPG), no planning permission on most houses since May 2025, and the default heating in new-build [SAP](/services/sap-calculations/) and under the [Future Homes Standard](/guides/future-homes-standard/). ## What ASHP means Air source heat pump. It is one of two families of heat pump you will meet — the other, the [ground source heat pump](/guides/ground-source-heat-pumps/) or GSHP, takes its heat from the ground through buried pipes instead. An ASHP takes it from the air, which is why it is a box with a fan on an outside wall rather than a trench in the garden, and why it costs a fraction of a GSHP to install. There are two types. **Air-to-water** heat pumps — the great majority of UK installations — heat the water in a wet central heating system: radiators or underfloor heating, plus a hot water cylinder. **Air-to-air** heat pumps blow warm air straight into the room through indoor units and generally do not provide hot water; they are what a reversible air-conditioning unit is. Everything on this page about SAP, grants and heating design is about air-to-water unless it says otherwise. ## How it works It runs a fridge in reverse, in four steps. A refrigerant at a very low temperature passes through the outdoor unit and **absorbs heat from the air**, evaporating as it does. A **compressor** squeezes the gas, and compressing a gas raises its temperature sharply. The hot gas then gives its heat up to the water in your heating circuit and **condenses** back to a liquid. Finally it passes through an **expansion valve**, drops in pressure and temperature, and goes round again. The trick is that the pump moves heat rather than making it. The electricity runs the compressor and the fan; the heat itself came free from the air. That is why one unit of electricity can deliver three or more units of heat, and why the physics still works when the air is below freezing — there is heat in air at any temperature above about minus 273°C, and modern units run down to about **minus 25°C**. The coldest UK design temperatures are only around minus 2 to minus 5°C. ## Efficiency — the three numbers, and the one that matters You will see three ratios, and they are not the same thing. **COP** — coefficient of performance — is an instantaneous figure at one set of test conditions. **SCOP** — seasonal COP — is a laboratory figure representative of a heating season, calculated to BS EN 14825 and quoted on the product label; current units are typically in the **3.5–4.5** range, higher at low flow temperatures. **SPF** — seasonal performance factor — is what the system actually did in a real house over a real year, and it is the figure that decides your bills. The largest UK field trial, the Electrification of Heat project, monitored 742 heat pumps for nearly two years. The **median SPF for air source was 2.80**, with the middle half of installations between 2.53 and 3.09, falling to about 2.44 on the coldest days. That gap between a label of 4 and a home at 2.8 is mostly design and installation: flow temperature, emitter sizing, controls and commissioning. In a well-insulated, airtight new build with underfloor heating or correctly sized radiators, the real figure sits at the top of that range. ## Running costs against gas Whether an ASHP is cheaper to run than a gas boiler comes down to one ratio: the price of a unit of electricity divided by the price of a unit of gas, set against the heat pump's SPF and the boiler's efficiency. For July to September 2026 the Ofgem price cap puts electricity at **26.11p per kWh** and gas at **7.33p** — a ratio of 3.56. Against a condensing boiler at 85% efficiency, a heat pump needs an SPF of about **3.0** to break even. From October the cap moves to 26.32p and 7.97p, a ratio of 3.30, and break-even drops to about **2.8** — right on the monitored median. On a flat standard tariff, then, a typical installation is roughly a draw with gas and a good one is ahead. A **heat pump time-of-use tariff**, with cheap overnight and off-peak periods, is what moves the sums decisively — and a new build designed around the pump from the start beats the median comfortably. ## The grant The **Boiler Upgrade Scheme** in England and Wales pays **£7,500** towards an air-to-water heat pump, and since 21 July 2026 **£9,000** for homes off the gas grid that are replacing oil or LPG heating — that uplift runs to 31 March 2027. Air-to-air heat pumps qualify for **£2,500**. The scheme has been extended to **2030**, the requirement to have an EPC was removed in 2026, and the earlier insulation conditions went in 2024. The installer must be MCS certified and commission within 120 days of the application. One grant per property. In **Scotland**, Home Energy Scotland offers a **£7,500 grant plus a £7,500 interest-free loan**, with an additional £1,500 on each for rural and island homes — up to £18,000 in all — for a heat pump that provides all the home's heating and hot water. The grant is for existing homes. In a **new build** there is no grant, and the heat pump is simply what the SAP expects — see below. ## Planning and noise For most houses in England an ASHP is **permitted development** — no planning application — and the rules were loosened on **29 May 2025**. The old requirement to keep the unit at least one metre from the boundary has been removed. The size limit for the outdoor unit rose from 0.6 to **1.5 cubic metres** for a house (0.6 for a block of flats). A detached house may have **two** units; any other house or a block of flats, one. The unit may not be used solely for cooling. What stayed: the unit must comply with the **MCS planning standard, MCS 020**, and permitted development still does not cover listed buildings, pitched roofs, flat roofs within a metre of the edge, or — in conservation areas and World Heritage Sites — walls or roofs facing a highway. MCS 020 is where noise comes in. Since September 2025 the test is a calculated sound level of **no more than 37 dB(A)** one metre from the centre of a neighbour's nearest habitable-room window, worked out from the unit's sound power, the distance and any barrier between them. (You may see 42 dB quoted; that was the old way of expressing the same limit and is superseded.) The unit itself typically runs at 40–60 dB up close; distance and siting do the rest, and on most plots a modern unit passes comfortably. ## Designing it properly The difference between a heat pump that returns 2.5 and one that returns 3.5 is nearly all design. The MCS design standard requires a **room-by-room heat loss calculation** to BS EN 12831-1 — not a rule of thumb from the boiler that was there before — at design temperatures for your location, and the pump has to meet **100% of that heat load without help from its backup electric heater**. Flow temperature is the lever: the standard steers designers to **55°C or below**, and the lower the better for efficiency, which is why radiators are often upsized and why underfloor heating suits heat pumps so well. A **hot water cylinder** is needed — the standard sizes it at 45 litres per person, counting bedrooms plus one — and the pump must be able to reach 55°C to heat it, with a legionella regime built in. Cylinders need a cupboard; plan for it. ## In the SAP calculation This is where an ASHP earns its place in a new build. SAP 10's carbon factor for electricity is **0.136 kgCO₂ per kWh** against **0.210 for mains gas**, and its primary energy factors are 1.50 and 1.13. Divide either by an SPF of 3 and a heat pump beats a gas boiler on both carbon and primary energy by a wide margin — often enough to carry the [SAP pass](/services/sap-calculations/) on its own, and the usual answer to a [planning renewables condition](/services/energy-statements/) too. The product has to be in the **PCDB**, the Product Characteristics Database that SAP draws its performance data from; a unit that is not listed gets conservative defaults and a worse result than it deserves, and an MCS certificate does not guarantee a PCDB entry. Tell us the make and model. Under the [Future Homes Standard](/guides/future-homes-standard/), in force from **24 March 2027**, the notional dwelling that new homes are measured against is heated by a heat pump — so the heat pump stops being the ambitious option and becomes the baseline. Gas boilers are not banned by name, but the government expects them to be effectively unviable in new homes. ## ASHP or GSHP? A [ground source heat pump](/guides/ground-source-heat-pumps/) runs a little more efficiently in deep winter, because the ground stays warmer than the air, and it makes no noise outside. It also costs several times as much to install and needs the land for a ground loop or the budget for a borehole. For most new builds the ASHP is the pragmatic choice — and the one the SAP will have assumed. --- # Ground Source Heat Pumps (GSHP) URL: https://energycount.co.uk/guides/ground-source-heat-pumps/ Updated: 2026-06-11 ## How a GSHP works A few metres down, the ground holds a stable temperature all year. A ground source heat pump circulates fluid through buried pipework — **horizontal loops** in trenches (needing significant land) or **vertical boreholes** (compact but costly to drill) — and upgrades that heat for space heating and hot water. Because the ground source doesn't drop with the air temperature, GSHPs deliver a higher, steadier **SCOP (typically 4+)** than air source units, with peak efficiency exactly when heating demand peaks. ## In the SAP calculation Everything said for [heat pumps generally](/guides/heat-pumps/) applies, with a better SCOP: a GSHP is usually the strongest heating entry a [SAP calculation](/services/sap-calculations/) can carry, and a robust answer to demanding [planning conditions](/services/energy-statements/). ## When it makes sense Install cost is the catch — groundworks or drilling put GSHPs well above [ASHPs](/guides/air-source-heat-pumps/). They earn their premium on larger dwellings with bigger heat demands, plots with available land, projects where the external unit of an ASHP is unwelcome, and multi-dwelling schemes using shared ground loops (increasingly popular, and well-treated in SAP). No outdoor fan unit also means silent operation. Weighing GSHP vs ASHP for a project? We'll model both in SAP so the decision is numbers, not guesswork. [Ask us](/contact/). --- # Solar Hot Water (Solar Thermal) URL: https://energycount.co.uk/guides/solar-hot-water/ Updated: 2026-06-11 ## How it works Solar thermal collectors — **flat plate** panels or **evacuated tubes** — absorb solar radiation and transfer the heat via a glycol loop to a coil in a twin-coil hot water cylinder. A well-sized system provides 50–60% of a dwelling's annual hot water, with the boiler or heat pump topping up. Per square metre, solar thermal converts sunlight to useful energy more efficiently than PV. ## In the SAP calculation SAP credits solar hot water against the dwelling's water-heating energy, improving the [DER](/guides/der-ter/) — a useful contribution, though smaller than what a decently sized [PV array](/guides/solar-pv/) achieves, because water heating is only part of a dwelling's energy balance. ## Solar thermal vs PV + diverter The market has largely moved to PV: panel prices fell, and a **PV diverter** (now recognised in [SAP 10](/guides/sap-10-whats-new/)) sends surplus PV generation into the immersion heater — heating water *and* offsetting electricity, with fewer roof penetrations, no glycol maintenance, and full credit in the calculation. Solar thermal still suits projects with high hot water demand and limited roof area. Unsure which suits your project and planning condition? [We'll model both](/contact/). --- # MVHR (Mechanical Ventilation with Heat Recovery) URL: https://energycount.co.uk/guides/mvhr/ Updated: 2026-06-11 ## How MVHR works An MVHR system continuously extracts stale, moist air from kitchens and bathrooms and supplies fresh air to habitable rooms, passing both streams through a heat exchanger. Up to ~90% of the heat in outgoing air transfers to the incoming supply — ventilation without the heat penalty of trickle vents and extract fans. The payoff: constant filtered fresh air, no condensation problems, and lower heating demand. ## The airtightness rule of thumb MVHR only makes sense in airtight dwellings. If the building leaks, uncontrolled infiltration delivers (cold) fresh air regardless and the heat exchanger achieves little — wisdom is that MVHR starts earning below roughly q50 = 3, and the tighter the better. That makes design-stage commitment essential: the [air test](/services/air-tightness-testing/) must deliver what the [SAP calculation](/services/sap-calculations/) assumes. ## In the SAP calculation SAP models MVHR through the system's heat-exchange efficiency and specific fan power, balanced against the dwelling's airtightness. In a tight dwelling it cuts ventilation heat loss substantially and helps the [DER and DFEE](/guides/der-ter/); in a leaky one it can model *worse* than natural ventilation once fan energy is counted. Duct design matters too — short, rigid, insulated runs. Get the SAP assumptions and ventilation design agreed together; we can advise on both. [Ask us](/contact/). --- # WWHR (Waste Water Heat Recovery) URL: https://energycount.co.uk/guides/waste-water-heat-recovery/ Updated: 2026-06-11 ## How WWHR works A waste water heat recovery unit is typically a vertical copper heat exchanger plumbed into the shower waste. Warm grey water spirals down the inside surface while incoming cold mains water passes around it, pre-warming the cold feed to the shower mixer and/or cylinder by recovering **around 40–60%** of the heat that would otherwise go down the drain. No moving parts, no electricity, no maintenance — it just sits in the pipework. Vertical units (through a floor) perform best; horizontal variants exist for ground-floor showers. ## Why SAP 10 made it standard The [SAP 10 notional dwelling assumes WWHR on all showers](/guides/sap-10-whats-new/) — so a dwelling without it starts behind target. For the modest cost of a unit per shower, WWHR is among the cheapest CO₂ and energy savings available in a [SAP calculation](/services/sap-calculations/), particularly in homes where showers dominate hot water use. It also helps [Part G water-energy crossover](/services/part-g-water-calculations/) thinking: shower flow rates now feed both calculations, so fittings choices pay off twice. Specify it at design stage — retrofitting into finished pipework is far harder. [Ask us](/contact/) where it earns most in your SAP. --- # FGHR (Flue Gas Heat Recovery) URL: https://energycount.co.uk/guides/flue-gas-heat-recovery/ Updated: 2026-06-11 ## How FGHR works Even a modern condensing boiler loses usable heat in its flue gases. A flue gas heat recovery device — fitted above or integrated into the boiler — captures part of that heat and uses it to pre-warm incoming water, mainly benefiting **domestic hot water** production. The boiler then needs less gas to reach temperature, typically saving a few percent of annual gas use, most in homes with high hot water demand. It's passive in operation, compact, and best specified with the boiler rather than retrofitted. ## In the SAP calculation SAP recognises FGHR through improved water-heating efficiency, helping the [DER](/guides/der-ter/) for gas-heated dwellings at modest cost. It pairs naturally with [WWHR](/guides/waste-water-heat-recovery/) — one recovers drain heat, the other flue heat. ## The bigger picture FGHR only applies to combustion boilers, so its future is bounded: the [Future Homes Standard](/guides/future-homes-standard/) removes fossil-fuel heating from new homes from 2027, and [heat pumps](/guides/heat-pumps/) have no flue to recover from. For conversion or extension projects keeping gas in the meantime, it remains a worthwhile line in the [SAP](/services/sap-calculations/) toolkit. [Ask us](/contact/) whether it earns its place in yours. --- # What is Weather Compensation? URL: https://energycount.co.uk/guides/weather-compensation/ Updated: 2026-06-11 ## How it works A weather compensator uses an external temperature sensor to modulate the heating flow temperature: bitter outside, hotter radiators; mild outside, cooler ones. Instead of cycling on and off at a fixed high temperature, the system runs longer, lower and steadier — keeping a condensing boiler in its efficient condensing range far more of the time, and keeping homes more evenly comfortable. For [heat pumps](/guides/heat-pumps/), weather compensation is essentially native: lower flow temperatures directly raise the SCOP, which is why almost every heat pump runs on a compensation curve. ## In the SAP calculation Heating **controls** carry real weight in SAP. Weather compensation (and load compensation, its indoor-sensing cousin) improves the modelled efficiency of the heating system, nudging the [DER](/guides/der-ter/) down for very little hardware cost — many boilers only need the sensor and a setting enabled. Modern boiler-interlock, time and zone control requirements still apply alongside. It's the kind of cheap specification line that's easy to forget and annoying to miss when a [SAP calculation](/services/sap-calculations/) is marginal. We'll flag it when it helps. [Ask us](/contact/). ## NEWS & REGULATION WATCH --- # Scotland has moved EPC reform to April 2028 — and it says something about the UK timetable URL: https://energycount.co.uk/news/scottish-epc-reform-delayed-april-2028/ Date: 2026-08-30 If you only work in England, a Scottish commencement date is easy to scroll past. This one is worth two minutes, because the Scottish Government has published its reasoning — and that reasoning is about the **UK-wide** Home Energy Model programme that everyone's compliance work eventually depends on. On **27 August 2026** the Scottish Government published an update confirming that the **Energy Performance of Buildings (Scotland) Regulations 2025** will now come fully into force on **30 April 2028**, rather than the 31 October 2026 date set when the Regulations were laid. ## What's actually changed The Energy Performance of Buildings (Scotland) Amendment Regulations 2026 do two things: - Move the full commencement date of the 2025 Regulations from **31 October 2026 to 30 April 2028**, and shift the saving and transitional provisions to match. - Allow the **lodgement fee** charged by the Keeper of the Register to rise **as already planned on 31 October 2026** — from **£2.60 to £6.00** for domestic properties, and from **£12.10 to £15.50** for other properties. Nothing else about the substance of the reforms changes. The new rating systems, the shorter five-year validity period, the redesigned certificate and Property Report and the strengthened quality-assurance regime all remain as approved by the Scottish Parliament in December 2025. The majority of the 2008 Regulations, and the EPC system assessors use today, stay in place until spring 2028. One part of the 2025 Regulations is already live: **Regulations 11 and 12**, covering the new Scottish EPC Accreditation Scheme and the appointment of Approved Organisations, came into force on **1 January 2026** and remain in force. The scheme is open to applicants now, ahead of the rest of the Regulations landing in 2028. ## Why the date moved — and why it matters in England The Scottish Government is explicit that this follows "extensive engagement with the UK Government and with the EPC assessor industry" on the delayed launch of new EPCs in England and Wales. Three points stand out: 1. **The UK Government's public commitment is still "the second half of 2027."** Scotland notes the UK Government had not reached final decisions on detailed implementation at the point Scotland had to lay its amending regulations to stop the 2025 Regulations biting on 31 October 2026. 2. **Scotland deliberately built in contingency.** Rather than match the second half of 2027, it planned for April 2028 to reduce the risk of having to amend the regulations again — and the market uncertainty that would cause. 3. **The underlying programme is shared.** The plan to finalise **HEM**, build and test the new **EPC Register** and the **Energy Calculation as a Service (ECaaS)** infrastructure, and train the assessor industry, "will remain the same across the UK." That third point is the useful one. The assessor market operates UK-wide and is partly covered by the UK Internal Market Act 2020, so the two governments are working to a common technical timetable even where commencement dates diverge. Scotland's stated expectation is that the infrastructure will be **tested and available for assessors to train on during 2027**. That's a reasonable read on when English assessors should expect HEM training to become real work rather than a diary note. ## The Scottish transitional arrangements, in brief If you do work north of the border, the transitions are worth knowing: - **Buildings for sale or let (other than short-term lets):** a one-year grace period from **30 April 2028 to 30 April 2029**. Old-style EPCs issued under the 2008 Regulations can still be *used* during that window, but from 30 April 2028 assessors can only *issue* new-style certificates. If a property is sold or let again within the transition, a new-style EPC is then required. After 30 April 2029, only new-style EPCs are allowed. - **Short-term lets:** the same full one-year grace period, recognising that around 30,000 Scottish short-term lets are continuously advertised and couldn't all be re-certified on day one. - **Large non-domestic buildings frequently visited by the public** (the display duty under Regulation 13): can keep displaying their existing old-style EPC until it expires or until **30 April 2033**, whichever comes first. - **New construction:** for buildings completed on or after **30 April 2028**, the developer must give the owner a valid new-style EPC and Property Report within **seven days** of submitting the completion certificate to the local authority verifier. This moves the requirement out of standard 6.9 of Schedule 5 to the Building (Scotland) Regulations 2004 and into the EPC regulations. Elmhurst also reports that the Scottish Government is aiming to launch the new **onsite audit regime in the second half of 2027** — ahead of the main reform date — and that the next changes to Scottish Building Standards, expected to use HEM, are currently planned for autumn 2029. That would leave an interim period where SAP is used for Building Standards compliance while HEM produces EPCs, which will need working through for the new-build sector. ## What to do about it For most English assessors and housebuilders, the practical answer is: nothing changes today. **SAP 10.3 remains the compliance methodology** for Part L and the Future Homes Standard, and the fabric work underneath it — U-values, air permeability, and thermal bridging — is exactly the same set of numbers whether the calculation engine is SAP or HEM later. That's the quiet advantage of a slipping methodology timetable. The inputs are stable even when the tool isn't. Junction detail and **PSI values** in particular carry more weight under the Part L 2026 targets than most schemes budget for, and modelled junctions beat default values by a margin that usually pays for itself. If you'd like your junctions modelled properly now — so the fabric is right whichever engine ends up running the numbers — [get in touch](/contact/) and we'll tell you how we'd approach it. *Sources: [Energy Performance Certificate Reform: updates — 24 August 2026 update, gov.scot (published 27 August 2026)](https://www.gov.scot/publications/energy-performance-certificate-reform-updates/) · [Energy Performance of Buildings (Scotland) Regulations 2025 — EPC reform consultations: SG response, gov.scot](https://www.gov.scot/publications/energy-performance-buildings-scotland-regulations-2025-update-government-response-epc-reform-consultations/) · [The Energy Performance of Buildings (Scotland) Regulations 2025 (SSI 2025/417), legislation.gov.uk](https://www.legislation.gov.uk/ssi/2025/417/contents/made) · [Scottish Government confirms EPC reform delayed until April 2028, Elmhurst Energy](https://www.elmhurstenergy.co.uk/blog/2026/08/28/scottish-government-confirms-epc-reform-delayed-until-april-2028/)* --- # Strategic sites get their own NPPF policy — and phasing is the whole point URL: https://energycount.co.uk/news/nppf-2026-strategic-sites-ho4-ho13/ Date: 2026-08-29 Last week we wrote about the [national section 106 templates aimed at 10–49 unit sites](/news/standard-s106-templates-medium-sites-consultation/). This is the other end of the same telescope. The **National Planning Policy Framework published on 17 August 2026** creates, for the first time, a distinct planning category for the very largest housing schemes — and the policies that govern it are almost entirely about phasing. For anyone doing SAP work on a strategic site, that is not a planning-nerd detail. It is the thing that decides which edition of Part L each phase is built to. ## What counts as a strategic site The Framework's plan-making policy, **HO4: Land for strategic site development**, describes them by type rather than by a bare number: > "The development plan should, where appropriate, identify suitable locations for strategic sites for housing-led development (such as new settlements, new urban quarters or significant extensions to existing settlements)." The Planning Portal, summarising the government's position on publication, reports that strategic sites will typically be those with capacity for **1,500 homes or more**, though the figure can vary with the mix of uses on the site. Treat that as the government's working scale rather than a hard threshold in the policy text. HO4 then sets three tests for the locations chosen. They should be capable of being supported by **the necessary infrastructure and facilities at appropriate points in the development's delivery**; capable of supporting a sustainable community with access to services and employment "without expecting an unrealistic level of self-containment"; and they should > "Address strategic environmental opportunities and safeguards, including those set out in Local Nature Recovery Strategies." Local plans are then expected to identify specific sites with their infrastructure and site-specific requirements, set design expectations through **masterplans and design codes**, make "a realistic assessment of the likely rates of delivery", and identify routes to rapid implementation such as joint ventures, land assembly or locally led development corporations. ## HO13 is where it gets practical The decision-making counterpart is **HO13: Build out of residential and strategic sites**. Paragraph 1 sets the general expectation that land with permission is developed without unnecessary delay, and paragraph 2 invites councils to consider conditions requiring development to begin sooner than the statutory default. Paragraphs 3 and 4 apply specifically to strategic sites. Paragraph 3 says the consenting framework should: > "a. Set out the parameters and requirements for the design, infrastructure and other features of the development (including the quantity and type of affordable housing to be provided), with the level of initial and subsequent detail tailored to the proposed scale and phasing of the development; and > > b. Be flexible enough to respond positively to changing circumstances as phases are brought forward, including changes to housing need, infrastructure requirements, viability and design." Paragraph 4 adds that where an emerging plan — "however advanced" — proposes to allocate strategic sites, development proposals should not be inconsistent with the proposed scale, location and phasing of those sites. So: parameters set early, detail scaled to phasing, and an explicit instruction that the consent should flex as phases come forward. ## Why this matters for Part L Here is the bit that lands on assessors' desks. A strategic site is, by definition, a scheme that will still be building out in ten years. The Future Homes Standard transitional arrangements are not that generous. As we've [written before](/news/future-homes-standard-transitional-deadline-commencement/), protection under **The Building Regulations etc. (Amendment) (England) Regulations 2026** (SI 2026/335) requires two things: a building notice, initial notice or full-plans application before **24 March 2027**, *and* the work on that individual building commenced before **24 March 2028** — with "commenced" meaning a completed sub-structure including ground floor structure, plot by plot. On a 1,500-home site, that is a small fraction of the programme. Phases one and possibly two might be protected. Everything after that is being built to ADL 2026 — heat pumps, on-site generation under requirement L3, and the tighter fabric that goes with them. HO13(3)(b) is helpful here, in a backhanded way. A consenting framework that is required to "respond positively to changing circumstances as phases are brought forward, including changes to... infrastructure requirements, viability and design" is one that ought to be able to absorb a change of Part L edition mid-build-out without a full section 73 fight. But that only works if the parameters set at outline are drafted to allow it. **The trap is a parameter plan or design code written to the fabric and services of the current regulations.** Fixed roof pitches and orientations that don't work for the PV array L3 now expects. Plot-wide glazing ratios set against a 2021 overheating assessment. External wall build-ups locked into a design code at a thickness that won't take the insulation ADL 2026 needs. Heat network capacity sized on the assumption every plot has a gas boiler. None of those are hard to fix at masterplan stage. All of them are expensive to fix at phase four. ## The other long-programme problems Two more that phasing makes worse rather than better. **Nutrient budgets.** In a protected catchment, the nutrient budget for a strategic site is calculated on the whole scheme, but the mitigation is usually delivered and paid for in tranches. If the budget was struck on an occupancy assumption or a wastewater treatment consent that changes between phase one and phase five, the arithmetic moves. The [new NPPF chapter on clean energy and water](/news/nppf-2026-clean-energy-and-water-w1-w4/) pushes catchment capacity into plan-making, which should mean fewer surprises — but only on plans prepared after August 2026. **Drainage.** HO4(1)(a) asks that infrastructure be capable of support "at appropriate points in the development's delivery". Surface water is the classic case where phase-by-phase attenuation designed in isolation adds up to a strategy that doesn't work at full build-out, and where the [national SuDS standards](/news/suds-strategy-templates-august-2026/) now expect a scheme-wide answer. ## What we'd suggest doing **Map your transitional cliff-edge against your phasing plan, on paper, now.** Which plots realistically get a full-plans application in before 24 March 2027 and a completed sub-structure before 24 March 2028? Everything to the right of that line is an ADL 2026 scheme. If nobody has drawn that line, the design code is being written blind. **Write the design code so it survives a regulation change.** Ask for parameter ranges rather than fixed values on the things Part L touches — wall thickness, roof form and orientation, plant space, glazing ratio. HO13(3)(b) gives you the policy hook to argue for it. **Get the fabric strategy tested against ADL 2026 before the code is fixed, not after.** A notional-building run on a representative house type from each phase is a day's work and will tell you whether the code you're about to adopt is buildable under the standard that most of the site will actually be built to. **Thermal bridging is the cheapest margin you have.** On a scheme with repeated house types across ten phases, bespoke PSI values are calculated once and used thousands of times. Default y-values on a 1,500-home site are, in aggregate, a very expensive convenience. **ΨMonkey** calculates bespoke PSI values for your junctions to BS EN ISO 10211, following BR 497 and BRE IP 1/06 conventions, in your browser — so your SAP model reflects the junctions in your design code rather than the worst case the software assumes. [Try ΨMonkey →](/tools/psi-calculator/) If you're masterplanning a site that will still be building out well past the Future Homes Standard transitional dates and you'd like the Part L strategy stress-tested before the design code is signed off, [get in touch](/contact/) — that conversation is much cheaper at outline than at phase four. *Sources: [National Planning Policy Framework, August 2026 (PDF), GOV.UK](https://assets.publishing.service.gov.uk/media/6a8334c03bd75b81e2329ac4/National_Planning_Policy_Framework.pdf) — chapter 6, policies HO4 and HO13 · [National Planning Policy Framework guidance page, MHCLG, 17 August 2026](https://www.gov.uk/guidance/national-planning-policy-framework) · [Government publishes latest NPPF with new strategic sites policy, Planning Portal Blog, 19 August 2026](https://blog.planningportal.co.uk/2026/08/19/government-publishes-latest-nppf-with-new-strategic-sites-policy/) · [The Building Regulations etc. (Amendment) (England) Regulations 2026 (SI 2026/335), legislation.gov.uk](https://www.legislation.gov.uk/uksi/2026/335/made)* --- # The NPPF now asks you to design against wildfire URL: https://energycount.co.uk/news/nppf-2026-wildfire-mitigation-cc3/ Date: 2026-08-29 England has had a summer marked by heatwaves, drought and wildfire damage to homes and habitats. The **National Planning Policy Framework published on 17 August 2026** responds with something national planning policy has never had before: a policy telling applicants to design against fire spreading in from the landscape. It is a short paragraph. It is also, for a certain kind of site, the thing that changes your landscape strategy and your boundary treatment specification. ## What CC3(1)(e) actually says Policy **CC3, "Adaptation to climate change"**, is a national decision-making policy. It opens by requiring development proposals to take into account the current and potential impacts of climate change *over the lifetime of the scheme*, then lists what that means in practice — flood risk, coastal change, SuDS, overheating, and now this: > "Incorporate proportionate measures to mitigate against wildfires, where opportunities to do so exist and wildfires pose a particular risk (for example as a result of the combined effect of topography, prevailing wind direction and being located within or adjacent to heavily vegetated areas). Such measures should be designed to limit fuel loads for fires, and to create defendable spaces, such as by avoiding timber panel fences and incorporating firebreaks into development layouts and planting schemes." Three things are worth pulling out of that. **It is conditional, not universal.** The duty bites "where opportunities to do so exist *and* wildfires pose a particular risk". Most urban infill will not engage it. The trigger the policy gives is a combination — topography, prevailing wind direction, and being within or adjacent to heavily vegetated areas. Heathland, forestry, moorland edge, gorse-covered slopes, plantation boundaries. **It names a specific product.** "Avoiding timber panel fences" is unusually prescriptive for the NPPF. Close-boarded timber fencing running from a vegetated boundary into a housing layout is a continuous fuel path, and the Framework says so in as many words. If your standard boundary detail on a rural-edge site is a 1.8m closeboard fence, that is now a policy conversation. **"Defendable space" is a design concept, not a buffer strip.** The wording asks for measures "designed to limit fuel loads" and to create defendable spaces, including **firebreaks in development layouts and planting schemes**. That is a masterplanning and landscape input, not something you bolt on at reserved matters — which means it needs to be in the layout at outline stage. ## And CC1 puts it into plan-making The plan-making counterpart, **CC1: Planning for climate change**, requires development plans to take a proactive approach to adapting to climate change > "taking into account the implications of extreme weather and long-term climate trends including overheating, wildfires, drought, flood risk, coastal change, water supply, biodiversity and landscapes" — and then to address "any specific risks from climate change in their proposed allocations for development, and necessary adaptations, both of which should be considered for the anticipated lifetime of the development". So wildfire is now something an emerging local plan is expected to have thought about when it allocates land. Expect it to start appearing in site-specific allocation policies and in the evidence base for rural and urban-fringe allocations over the next plan-making round. ## Where this sits next to the rest of the climate chapter Chapter 5 is compact — CC1 for plan-making, CC2 for mitigation, CC3 for adaptation — and CC3 now bundles four adaptation duties into one list: flooding, coastal change, [sustainable drainage under policy F8](/news/nppf-2026-suds-national-standards-policy-f8/), [overheating under DP3(2)(b)](/news/nppf-2026-overheating-policy-cc3/), and wildfire. That grouping matters. It means a single planning officer, reading one policy, is now looking for evidence on all four. On a rural-edge site in a hot, dry catchment you could plausibly be asked at validation for a drainage strategy, an overheating assessment and a note on wildfire mitigation — three things that until this month sat in three different places, two of them in Building Regulations rather than planning. There is also a tension worth naming. **CC3(1)(d)** asks for green infrastructure and tree planting to minimise overheating risk. **CC3(1)(e)** asks you to limit fuel loads. On most sites those pull in the same direction — shade trees near dwellings, managed grassland, irrigated planting. On a dry heathland edge they do not, and the policy gives no hierarchy. Someone will have to reconcile that in a design and access statement, and the sooner your landscape architect is in the room the cheaper that is. ## What we'd suggest doing **Work out whether you're actually in scope.** The test is topography plus prevailing wind plus adjacency to heavy vegetation. If your red line abuts forestry, heath, moorland or unmanaged scrub on the upwind side of a slope, assume the question will be asked and get ahead of it. If you're in a town centre, it won't be. **Look at your boundary treatment standard detail now.** Timber closeboard is named in national policy as the thing to avoid. Substituting masonry, metal railings or hedge-on-post on the vegetated boundary is cheap at design stage and expensive at condition-discharge stage. **Put firebreaks in the layout, not the landscape schedule.** The policy talks about "development layouts and planting schemes" together. Layout is fixed at outline; planting is not. If the mitigation lives entirely in the soft landscaping, you have less room to move later. **Don't let it undercut your overheating design.** Part O has not changed — the [2021 edition is still the one in force](/news/record-summer-2026-part-o-overheating-gap/) while the promised full review runs its course — and CC3(1)(d) still expects overheating to be designed out. Wildfire mitigation should reshape *where* the planting goes and *what species*, not delete it. ## If you're already doing the overheating work For most of our clients, the practical effect of chapter 5 is that climate adaptation evidence is now something planning asks for, months before Building Control does. Overheating is the one that costs money if you get it wrong late — a TM59 failure at Part O stage on a scheme already consented with a fixed glazing ratio is an expensive conversation. If you have a site coming forward on a rural or urban-fringe edge and you'd like the overheating, drainage and adaptation evidence lined up before validation rather than after, [get in touch](/contact/) and we'll tell you what we'd want to see modelled first. *Sources: [National Planning Policy Framework, August 2026 (PDF), GOV.UK](https://assets.publishing.service.gov.uk/media/6a8334c03bd75b81e2329ac4/National_Planning_Policy_Framework.pdf) — chapter 5, policies CC1 and CC3 · [National Planning Policy Framework guidance page, MHCLG, 17 August 2026](https://www.gov.uk/guidance/national-planning-policy-framework) · [Revised National Planning Policy Framework published: what it means for ecology and environmental management, CIEEM, 20 August 2026](https://cieem.net/revised-national-planning-policy-framework-published-what-it-means-for-ecology-and-environmental-management/)* --- # National s106 templates are coming for 10–49 unit sites URL: https://energycount.co.uk/news/standard-s106-templates-medium-sites-consultation/ Date: 2026-08-28 If you work on schemes of 10 to 49 homes, the section 106 agreement is often the thing that decides whether permission arrives in three months or nine. On **25 August 2026** MHCLG published a consultation on **four standard s106 templates** aimed squarely at that size of site. It runs for eight weeks, closing at **11:59 on 20 October 2026**, and applies to **England only**. ## What's being consulted on The consultation covers four draft documents, drafted for MHCLG by **Town Legal LLP** working with the Planning Advisory Service: 1. **Bilateral agreement** — standard clauses, plus schedules for Financial Contributions and the Council's Covenants. 2. **Unilateral Undertaking** — standard clauses, plus a schedule for Financial Contributions. 3. **Affordable Housing Schedule for Full Planning Permissions**, including a discretionary cascade mechanism. 4. **Affordable Housing Schedule for Outline Planning Permissions**. The draft templates are published alongside the consultation document, and there are 80 questions to respond to. ## "Medium-sized" now has a formal definition The threshold comes from the **new NPPF published on 17 August 2026**, which, as the consultation puts it, "formally introduces the category of 'medium' development (schemes of up to 2.5 hectares in area and between 10 and 49 units)." That's a meaningful change from the earlier proposal, which had floated 10–49 units on sites of up to **1.0 hectare**. The area limit has more than doubled, so the templates will catch a lot more of the typical SME site than first proposed. ## These aren't optional in practice The templates are not legally mandatory, but the new NPPF gives them real weight. The consultation points to **policy DM6(4)**, which > "sets out … that where national model planning obligations are relevant to the development, they should be used unless there are strong reasons for using a different obligation." MHCLG is explicit about the intent: the templates are "intended to become the default for applications in the future, reducing time spent agreeing standard provisions and freeing up local capacity to focus negotiations on more complex obligations." Government also says it "intends to publish further model obligations and planning conditions to support consistency in decision making in due course." The one carve-out is the affordable housing **cascade mechanism**, which is proposed as discretionary for councils to use where they think it appropriate. ## The bit that matters for environmental obligations Here's the part worth understanding properly. **The templates are content-neutral shells.** Affordable housing is the only substantive obligation actually drafted. Everything else — nutrient mitigation payments, SuDS and drainage maintenance sums, biodiversity net gain contributions, open space, education, highways — is left to be inserted into **Schedule 2** as a named "Contribution". We checked the consultation document carefully, and it does not mention energy efficiency, carbon, Part L, the Future Homes Standard, water efficiency, nutrient neutrality, phosphates or nitrates, biodiversity net gain, SuDS, sustainable drainage, flood risk, overheating or EV charging anywhere. Not once. None of the 80 questions asks about them either. That isn't necessarily a criticism — a template that tried to draft every environmental obligation for every catchment in England would be unusable. But it does mean the standardisation stops exactly where the technical work starts. Schedule 2 works as a repeatable pro-forma: as the consultation explains, "for each contribution, or instalment of a contribution, sub clauses (a) and (b) will need to be copied and completed with the name of the contribution and the relevant date." For outline permissions, where the sum depends on the quantum approved at reserved matters, "the formula for calculating the contribution should be included." So on a nutrient-constrained site, your phosphate or nitrogen mitigation payment is still a bespoke figure that someone has to calculate, justify against the **Regulation 122 CIL tests** (necessary, directly related, and fairly and reasonably related in scale and kind), and drop into a blank line in an otherwise standard document. ## Other practical points - **Payment triggers.** Schedule 2 provides for payment before specified points such as commencement or first occupation, and MHCLG acknowledges instalments linked to build-out, occupation of a set number of dwellings, or phases. - **Indexation.** There's a dedicated indexation clause, and question 30 asks which indices are appropriate for particular types of contribution. If you've ever watched a nutrient credit price move between agreement and payment, that question is worth answering. - **Unspent money.** The bilateral agreement's Schedule 3 requires contributions to be used solely for the purpose secured and held in an interest-bearing account, with a default five-year repayment window for unspent sums. Question 56 asks whether councils should instead be able to spend unclaimed sums on other mitigation in the vicinity. - **Still site-specific.** MHCLG is clear that "agreements must therefore be considered on a site-by-site basis to ensure that they are appropriate for a particular development." ## Why this is worth ten minutes of your time The stated problem is a familiar one. In MHCLG's words, s106 negotiation "has become synonymous with inefficiency and delay, which demands significant local authority resources and can have a disproportionately negative impact on Small and Medium Enterprise (SME) builders." If that lands with you, the consultation is a genuine chance to shape the drafting — particularly on indexation, payment triggers and how environmental contributions get expressed. Responses go through Citizen Space, with enquiries to standards106consultation2026@communities.gov.uk. For most schemes at this size, though, the s106 was never the hard part. The hard part is arriving at a defensible mitigation figure in the first place — and on a nutrient-constrained catchment that means a nutrient budget that stands up to Natural England scrutiny, for both nitrogen and phosphorus where the catchment demands it. If you'd rather have that number settled before the s106 conversation starts, [get in touch](/contact/) and we'll tell you how we'd approach your site. *Sources: [Standard planning agreements for medium-sized sites, GOV.UK (published 25 August 2026)](https://www.gov.uk/government/consultations/standard-planning-agreements-for-medium-sized-sites) · [Consultation document (full text), GOV.UK](https://www.gov.uk/government/consultations/standard-planning-agreements-for-medium-sized-sites/standard-planning-agreements-for-medium-sized-sites) · [Letter from MHCLG to Chief Planning Officers, 25 August 2026, GOV.UK](https://www.gov.uk/guidance/planning-guidance-letters-to-chief-planning-officers) · [The Planning Jungle summary, 27 August 2026](https://planningjungle.com/2026/08/27/the-government-publishes-a-consultation-until-20-10-2026-relating-to-standard-planning-agreements-for-medium-sized-sites/)* --- # Your soakaway test was done in the driest ground for years URL: https://energycount.co.uk/news/bre-365-soakaway-testing-drought-conditions/ Date: 2026-08-27 Here's a scenario worth thinking about before autumn submissions go in. A soakage test carried out in August 2026 comes back with a healthy infiltration rate. The soakaway is sized accordingly, the drainage strategy is approved, and the thing is built the following spring — into ground that behaves nothing like it did in the test pit. ## Why this year is different The Environment Agency's report for **14 to 20 August 2026** records that the **seasonal recession of groundwater levels is continuing**, with levels in the Oolite Limestone aquifers **exceptionally low in places** and some chalk sites in the Wessex Downs, Yorkshire Wolds and the North and South Downs classed as below normal or notably low. A quarter of monitored river sites are exceptionally low, and **71% of England by land area is in drought** ([GOV.UK](https://www.gov.uk/government/publications/dry-weather-and-drought-in-england-2026-summary-reports/dry-weather-and-drought-in-england-14-to-20-august-2026)). That follows what the Environment Agency has called the **driest July in 190 years**. The agency also notes a related effect worth holding onto: with ground conditions this dry, **water does not easily soak into baked and compacted soils**, increasing run-off risk. Very dry ground can behave in ways that don't map neatly onto either summer or winter design assumptions. ## What BRE Digest 365 actually asks of you [BRE Digest 365, *Soakaway design* (2016 edition)](https://bregroup.com/store/bookshop/soakaway-design-dg-365-2016-download) is still the standard reference for infiltration testing — our [BRE Digest 365 soakaway calculator](/tools/soakaway-calculator/bre-digest-365/) runs the full method, and the [percolation test calculator](/tools/soakaway-calculator/percolation-test/) turns the pit timings into the infiltration rate. Two features of the method matter here. First, it is deliberately conservative about the test itself: the design rate is taken from **the lowest of up to three tests** in a pit, not an average of them. That guards against one flattering fill-and-drain cycle carrying the design. Second — and this is the one that gets skipped — the method assumes you know where the water table is going to be. **Groundwater levels move seasonally**, so evidence of the **highest likely water table** is normally needed alongside the test result. Standard practitioner guidance for sites with a seasonally high water table, such as lowland areas or land near a watercourse, is to test in **winter or spring, when the table is highest** — precisely the opposite of the conditions available across much of England right now. There is a wider professional argument running about how reliable BRE 365 results are in general — susdrain hosts an [Environmental Protection Group briefing](https://www.susdrain.org/files/resources/briefings/EPG_Briefing_SoakwayTesting_V2.pdf) asking whether the test has had its day. You don't need to take a side in that debate to accept the narrower point: a test done in the driest ground in living memory carries more uncertainty than usual. ## Why the stakes just went up Drainage evidence used to be something you could largely settle after permission. That's changed. Under the August 2026 NPPF, **policy F8** requires SuDS on all development with drainage implications to be designed in accordance with Defra's National Standards, and **policy DM2** puts a site-specific flood risk assessment and a SuDS statement on a national validation list. The Environment Agency and CIRIA have published **national SuDS Strategy Templates** for major and non-major development to standardise what gets submitted. So the infiltration rate is now load-bearing at validation, not just at discharge of conditions. If it turns out to be optimistic, you're not correcting a detail — you're revisiting an approved strategy, potentially with a different discharge route and a different land take. ## Five things worth doing **Record the test date and antecedent conditions.** Note rainfall in the preceding weeks and the groundwater context. A reviewer six months from now needs to know the test was run in a drought, and so do you. **Get separate groundwater evidence.** Don't infer the winter water table from an August pit. Borehole records, published aquifer data or a monitoring period give you something defensible. **Consider retesting in the wet season** on marginal sites, or designing with an explicit margin and stating why. **Know your fallback.** If the rate is genuinely marginal — broadly, once you're heading below about 10⁻⁶ m/s, infiltration stops being practical — establish the next step in the discharge hierarchy early rather than discovering it at construction. **Keep three tests, and use the lowest.** It's the method, and in a year like this one it's also the only sensible instinct. ## Size it properly, quickly **SoakMonkey** does BRE Digest 365 soakaway sizing in your browser — enter your test results, get a defensible design and a printable output for the drainage strategy. It won't tell you whether your test was done in the right season, but it will make the rest of the job take minutes. [Try SoakMonkey →](/tools/soakaway-calculator/) *Sources: [GOV.UK — Dry weather and drought in England: 14 to 20 August 2026](https://www.gov.uk/government/publications/dry-weather-and-drought-in-england-2026-summary-reports/dry-weather-and-drought-in-england-14-to-20-august-2026) · [BRE Digest 365 — Soakaway design (2016)](https://bregroup.com/store/bookshop/soakaway-design-dg-365-2016-download) · [susdrain — EPG briefing on soakaway testing](https://www.susdrain.org/files/resources/briefings/EPG_Briefing_SoakwayTesting_V2.pdf) · [Environment Agency blog, 12 August 2026](https://environmentagency.blog.gov.uk/2026/08/12/how-the-environment-agency-manages-abstraction-to-protect-the-environment/)* --- # 71% of England is in drought — and it's now a planning problem URL: https://energycount.co.uk/news/drought-71-percent-england-water-efficiency-august-2026/ Date: 2026-08-27 Water efficiency has spent years as the quiet part of a Building Regulations submission — a fittings schedule, a calculation, a number under 125. That framing is getting harder to sustain. ## What the Environment Agency published On **21 August 2026** the Environment Agency published its weekly summary covering **14 to 20 August** ([GOV.UK](https://www.gov.uk/government/publications/dry-weather-and-drought-in-england-2026-summary-reports/dry-weather-and-drought-in-england-14-to-20-august-2026)). The headline numbers are worth reading properly: - **71% of England by land area is in drought**, with no change in area status that week. - **Reservoir storage for England was 62.6% on 18 August** — down 3.4% in a single week, and **16.3% below average** for the time of year. Seven major reservoirs are classed as exceptionally low. - **August rainfall to date was 17% of the long-term average** for England, ranging from 5% in the south east to 33% in the north west. - **A quarter of monitored river sites are classed as exceptionally low**, predominantly across southern and eastern England. - **Around 29 million people** are under temporary use bans, after Affinity Water extended its ban to its eastern region on 17 August and Wessex Water went company-wide on 18 August. - **1,562 restrictions on abstraction licences** are in place, including mandatory Section 57 spray irrigation reductions in parts of East Anglia running to **31 October**, cutting abstraction by 50% across 288 licences. - **226 drought and dry-weather incidents** have been confirmed since the start of 2026. The **National Drought Group was reconvened on 20 August** and is now meeting weekly. This follows a July the Environment Agency has described as the **driest in 190 years** ([EA blog, 12 August 2026](https://environmentagency.blog.gov.uk/2026/08/12/how-the-environment-agency-manages-abstraction-to-protect-the-environment/)). Areas in drought now include East Anglia, Thames, Kent and South London, Hertfordshire and North London, Solent and South Downs, Wessex, the West Midlands, the East Midlands, Lincolnshire and Northamptonshire, and Devon, Cornwall and the Isles of Scilly. Four further areas are in prolonged dry weather. ## Why this lands on your desk Most of those catchments are exactly where housing is being delivered — and where water is already a live constraint on consent. Three connections matter. **Part G is moving.** The current national standard is 125 litres per person per day, with a 110 l/p/d optional requirement available through planning conditions. Defra has consulted on tightening these to **105 and 100 l/p/d**. Nothing in the drought changes the legal position today, but it does change the political weather around the response. **Local standards survived the NPPF rewrite.** The August 2026 Framework confirms that local plans may apply the tighter Part G optional requirement where justified, and exceptionally a more stringent local standard in areas of serious water stress. That patchwork isn't going away this autumn — if anything, expect more authorities to reach for it. **Water availability is being tested at application stage.** New NPPF policies require plan-making to be informed by early engagement with water and wastewater providers on capacity, and several catchments already operate water neutrality or offsetting regimes. A scheme that clears Part G on paper can still stall on supply. ## The practical version If you're producing water efficiency evidence this autumn, a few things are worth doing now rather than at discharge-of-conditions: Check whether the authority has adopted the 110 l/p/d optional requirement, and whether a local plan policy goes further — don't assume 125 is the target. Design to the standard you're likely to be held to, not the one that was in force when the site was first appraised. Keep the fittings schedule and the calculation together in one auditable pack, because Building Control and the LPA are increasingly asking to see the same evidence. And if the site sits in a water neutrality or offsetting area, treat that as a separate workstream with its own lead time — it is not a Part G calculation with extra steps. None of this is new regulation. It's the same rules being applied in a much less forgiving environment. ## Get the water calculation right first time **WaterMonkey** runs the Part G water efficiency calculation in your browser — 125, 110 or a local standard — and gives you a fittings schedule you can hand straight to Building Control. One less thing to redo when the target moves. [Try WaterMonkey →](/tools/part-g-water-calculator/) *Sources: [GOV.UK — Dry weather and drought in England: 14 to 20 August 2026](https://www.gov.uk/government/publications/dry-weather-and-drought-in-england-2026-summary-reports/dry-weather-and-drought-in-england-14-to-20-august-2026) · [Environment Agency blog — managing abstraction, 12 August 2026](https://environmentagency.blog.gov.uk/2026/08/12/how-the-environment-agency-manages-abstraction-to-protect-the-environment/) · [Defra — Review of water efficiency standards in the Building Regulations](https://consult.defra.gov.uk/water-efficiency-demand/review-of-water-efficiency-standards)* --- # Mayors are getting call-in powers — and 150 homes is the threshold URL: https://energycount.co.uk/news/mayoral-planning-powers-consultation-october-2026/ Date: 2026-08-27 If you work on schemes of any size, the question of *who decides* is about to change in a lot of England. On **23 August 2026** the Prime Minister's Office announced that mayors across England will be given "call in" powers over the most important planning decisions in their areas ([GOV.UK press release](https://www.gov.uk/government/news/mayors-given-powers-to-green-light-developments)). The detail landed the following day: MHCLG's consultation, **Planning powers for mayors in England**, opened on **24 August 2026** and runs for six weeks, closing at **23:59 on 5 October 2026**. ## The thresholds This is the first time national thresholds for strategic call-in have been set outside London. Under the announcement, applications in scope are: - **more than 150 homes** - **more than 15,000 m² of commercial floorspace** - **any building over 30 metres tall** — roughly ten storeys A mayor will be able to take over a qualifying application and direct the council to approve or refuse it. Councils will continue to determine the large majority of applications, every decision must still follow planning law, the development plan and national policy, applicants keep their right of appeal, and ministers retain a backstop power to intervene. Worth noting for anyone modelling risk on a marginal site: the consultation observes that the 150-dwelling and 15,000 m² categories would **align with the thresholds for the Secretary of State's new and proposed consultation directions** where an authority proposes to refuse. In other words, the same scale of scheme is picking up attention from two directions at once. ## The part that changes when your evidence is due The consultation has four parts — call-in of applications of potential strategic importance, **Mayoral Development Orders (MDOs)**, **Mayoral Community Infrastructure Levy (MCIL)**, and some further changes to Local Development Orders. The MDO section is the one worth reading if you produce technical evidence. An MDO is an **upfront grant of planning permission by a mayor for development on a particular site** — no planning application needed. The powers sit at [sections 61DA to 61DE of the Town and Country Planning Act 1990](https://www.legislation.gov.uk/ukpga/1990/8/part/III/crossheading/mayoral-development-orders), originally introduced for the Mayor of London by the Infrastructure Act 2015 and updated by the English Devolution Act. The proposed process is modelled on Local Development Orders: a draft order plus a **statement of reasons**, a minimum **30-day** publicity and consultation period, notification of owners, occupiers and the local planning authority, and a duty on the mayor to consider representations before adopting the order. The consultation is explicit that key planning matters have to be settled early. It says it will be important to ensure that **environmental mitigations and the likely infrastructure requirements to be secured through planning obligations** are considered early in the process, along with the mechanism for discharging any subsequent conditions and who the approving authority for those will be. Translated into working terms: on an MDO site, the drainage strategy, the overheating position, the nutrient or water position and the energy standard don't sit behind a pre-commencement condition to be argued about later. They inform whether the order gets made at all, and the consenting framework it sets. That's the front-loading everyone has been talking about since the NPPF restructure, made concrete. ## Timing The government says it wants the call-in and MDO powers **in place by early next year**, and — subject to consultation and parliamentary scheduling — intends to **lay the MDO secondary legislation by the end of 2026**. MCIL outside London depends on a Spatial Development Strategy being in place in the relevant area, and would fund a broader range of strategic infrastructure than the London model, which is limited to strategic transport. Two limitations are proposed on MDO scope, including an exclusion for **minerals development**. ## What to do about it If you regularly work on schemes at or above 150 homes, this is worth twenty minutes. The thresholds, the MDO procedure and the question of who discharges conditions under an order are all live questions in the consultation, and the answers will shape how early your technical evidence has to be finished. Responses close at **23:59 on 5 October 2026** via the [consultation page on GOV.UK](https://www.gov.uk/government/consultations/planning-powers-for-mayors-in-england/planning-powers-for-mayors-in-england). If your view is that upfront consenting only works when the drainage, overheating and water evidence is genuinely resolved at order stage, that's exactly the kind of practitioner feedback Part 2 is asking for — so say it. *Sources: [GOV.UK — Planning powers for mayors in England (consultation)](https://www.gov.uk/government/consultations/planning-powers-for-mayors-in-england/planning-powers-for-mayors-in-england) · [GOV.UK — Mayors given powers to green light developments, 23 August 2026](https://www.gov.uk/government/news/mayors-given-powers-to-green-light-developments) · [MHCLG in the Media, 26 August 2026](https://mhclgmedia.blog.gov.uk/2026/08/26/coverage-of-plans-to-strengthen-mayoral-powers-over-planning-decisions/)* --- # A small planning change aimed at grid delays — and it closes on 4 September URL: https://energycount.co.uk/news/grid-ground-investigations-permitted-development-consultation/ Date: 2026-08-26 Ask a housebuilder what's actually stopping a site right now and grid connection comes up as often as anything in the planning system. It's a strange constraint to explain to a client: the homes are consented, the design is fixed, and the thing holding it up is a substation upgrade with a date three years out. There's a small consultation open at the moment that's aimed squarely at one corner of that problem, and it closes soon. ## What's proposed On **6 August 2026**, the **Department for Energy Security and Net Zero** published a consultation on **new permitted development rights for ground investigations and surveys** carried out to support electricity network infrastructure projects in England. It was flagged to every local planning authority in the **Chief Planner's Planning Update Newsletter of 18 August 2026**, which asked councils to engage with it. The proposal is narrow. It would introduce a permitted development right for **certain temporary, low-impact ground investigations and surveys** undertaken by **electricity network developers** — specifically the distribution and transmission network operators licensed to carry out works relating to electricity networks. It does not grant permission for the infrastructure itself. The consultation is **open until 4 September 2026**. ## Why a survey PD right matters to a housing programme This looks like a technical change for utilities, and in the strict sense it is. But it sits on a chain of events that developers wait on. Before a network operator can design and cost a reinforcement — a new substation, a cable route, an upgraded feeder — it needs ground information: trial pits, boreholes, geophysical and environmental surveys along the route. If each of those needs its own planning application, the front end of the process gains weeks or months before any design work starts, and every one of those weeks lands somewhere in a connection date that a housebuilder is planning around. Bringing that survey work inside permitted development is an attempt to take that step off the critical path. It's a modest change. But delays of this kind compound, and this is the sort of unglamorous fix that shortens programmes without changing the substantive planning tests on anything. It also fits a pattern. In April 2026 the government confirmed it will raise the permitted development threshold for **electricity substations in England from 29 to 45 cubic metres**, bringing England into line with Scotland so network operators can deliver capacity upgrades with less administrative friction. This consultation extends the same logic upstream, to the investigation work that precedes the design. ## The Future Homes Standard connection This matters more from **24 March 2027** than it did before. Under [Approved Document L 2026](/news/future-homes-standard-adl-2026/), new homes will no longer use fossil fuel heating. Heating and hot water move to electricity — heat pumps or heat networks — with on-site renewable generation under the new PV requirement. Which means a new development's electrical load profile is fundamentally different from a gas-heated equivalent: higher peak demand, heat pumps and EV charging, and PV export back onto the network. In other words, the Future Homes Standard makes every new site a bigger ask of the local network at exactly the point when connection queues are already the binding constraint. Anything that shortens network reinforcement lead times is, indirectly, a Part L delivery measure. The new [NPPF chapter on securing clean energy and water](/news/nppf-2026-clean-energy-and-water-w1-w4/), published 17 August 2026, made the same point from the planning side: policies W1 to W4 put network capacity into plan-making and give substantial weight to the infrastructure that fixes it. This consultation is the deregulatory half of the same argument. ## Should you respond? If you're a housebuilder or developer with sites where a connection date is driving the programme, this is a short consultation with a specific question, and the case for it is one you can evidence better than most people — you know what a slipped connection date costs. Worth saying plainly: this is a proposal about surveys, not about capacity. It will not conjure headroom on a constrained network, and nobody should tell a client it will. But the front end of a reinforcement is one of the few parts of the chain where planning reform can actually move the date, and the consultation is open for another week and a bit. Local planning authorities have been asked to engage with it directly. If you deal with an LPA that has been vocal about grid constraints in its local plan evidence base, it's worth checking they've seen it. **The consultation closes on 4 September 2026.** --- If you're planning around a Future Homes Standard changeover and want to know where your plots sit on the [24 March 2027 and 24 March 2028 transitional dates](/news/future-homes-standard-transitional-deadline-commencement/), [get in touch](/contact/) — that's the deadline we get asked about most, and the definition of "commenced" catches people out. *Sources: [Letter from MHCLG to Chief Planning Officers — Planning Update Newsletter, 18 August 2026 (PDF)](https://planningjungle.com/wp-content/uploads/Letter-from-MHCLG-to-Chief-Planning-Officers-Planning-Update-Newsletter-18-August-2026.pdf) · [Planning guidance letters to chief planning officers, GOV.UK](https://www.gov.uk/guidance/planning-guidance-letters-to-chief-planning-officers) · [Electricity network infrastructure: consents, land access and rights — government response, GOV.UK](https://www.gov.uk/government/consultations/electricity-network-infrastructure-consents-land-access-and-rights/outcome/electricity-network-infrastructure-consents-land-access-and-rights-government-response) · [DESNZ publishes a consultation (until 04/09/2026) relating to permitted development rights for ground investigations and surveys for electricity network infrastructure, The Planning Jungle, 12 August 2026](https://planningjungle.com/2026/08/12/desnz-publishes-a-consultation-until-04-09-2026-relating-to-permitted-development-rights-for-ground-investigations-and-surveys-for-electricity-network-infrastructure/)* --- # The hottest summer on record — and a Part O that hasn't moved since 2021 URL: https://energycount.co.uk/news/record-summer-2026-part-o-overheating-gap/ Date: 2026-08-26 Overheating assessments get done against a fixed rulebook. The weather does not read it. On **11 August 2026** the Met Office published provisional statistics showing the UK on course for its **warmest summer on record for mean temperature**. It's worth reading the numbers properly, because they're the backdrop to every Part O conversation you'll have this autumn. ## What the Met Office actually published From **1 June to 10 August 2026**, the UK mean temperature stood at **16.48°C — 1.88°C above the 1991–2020 average**. The existing UK record is **16.12°C, set in 2025**. To merely *equal* that record, the rest of August would have had to average 0.21°C below the long-term summer average. Anything warmer sets a new record, in a series that starts in **1884**. England and Wales are further ahead again: | Area | Mean temp (1 Jun – 10 Aug 2026) | Difference from average | Current record | | --- | --- | --- | --- | | UK | 16.48°C | +1.88°C | 16.12°C (2025) | | England | 18.19°C | +2.46°C | 17.44°C (2025) | | Wales | 16.80°C | +2.17°C | 16.09°C (2025) | Met Office senior scientist Mike Kendon noted this followed the **second-warmest June and second-warmest July on record**, with 38°C reached in June and 35°C in both late May and July. The 1976 record for average *maximum* temperature was also described as under threat. Two things are worth separating here. A single hot summer is weather, not a methodology change. But the direction is consistent — and 2025 held the previous record, which tells you something about how quickly the reference points are moving. ## Meanwhile, the compliance position hasn't moved Here's the awkward part for anyone designing homes right now. **Approved Document O is still the 2021 edition.** When MHCLG published the Future Homes Standard package on 24 March 2026, Part O was pulled out of it. Instead of an updated AD O alongside the new Parts L and F, the government announced a **standalone full review of Part O**, reflecting the volume of issues raised at consultation. That review has **no published date**, and because Part O sits outside the Future Homes Standard transitional window, it does not automatically share the 24 March 2027 in-force date that applies to Parts L and F. **The dynamic modelling methodology has moved on without it.** CIBSE published a substantially revised [**TM59:2026**](/news/cibse-tm59-2026-overheating-update/) in July — a passive-first three-stage method with four assessment criteria and a rewritten bedroom night-time test. Approved Document O still points at the 2017 edition. If you run a dynamic assessment, you now have to be explicit about which edition you've used and why, because your Building Control body may not assume the same one you did. **Planning has moved too.** Since **17 August 2026**, [NPPF policy **CC3**](/news/nppf-2026-overheating-policy-cc3/) requires development proposals to use design approaches which minimise risks from overheating. That's a decision-making policy applying at planning — years ahead of any revised AD O. So the practical position is a widening gap: the evidence base is getting hotter, planning has an overheating test, the modelling methodology has been rewritten, and the statutory guidance is five years old. ## What this means on a live job A few things worth doing now rather than in a year's time: - **Don't treat the simplified method as free.** The Part O simplified method was written against a different climate baseline. Where a plot is borderline — south or west glazing, single aspect, urban site with restricted openable area — a dynamic assessment gives you evidence you can defend at both planning and Building Control. - **State your TM59 edition.** Put it in the report front sheet. If you use TM59:2026, say so; if you use the 2017 edition because AD O references it, say that too. Ambiguity is what gets queried. - **Deal with overheating at planning, not after.** Under CC3 a planning officer can now ask the question, and retrofitting a fix after permission — deeper reveals, external shading, changed window schedules — is expensive and often unpopular with the elevations. - **Watch the interaction with Part L.** The FHS package already recognises this: where air conditioning or reduced g-value glazing is installed to comply with Part O, the Part L 2026 standards account for the resulting energy use, so you aren't penalised twice for the same design decision. That's a change in your favour — use it. - **Remember airtightness cuts both ways.** Tighter fabric under FHS makes purge and night ventilation strategies more important, not less. A home that can't dump heat overnight is a home that fails a night-time criterion. ## The honest summary Nothing in the Met Office release changes a single input in your model this week. What it changes is the risk profile of the assumption that a marginal pass today will still look marginal in ten years — and the likelihood that when the Part O review does land, it lands harder rather than softer. If you've got a scheme where overheating is close to the line, that's the one to model properly now. If you've got a plot where overheating is close to the line — flats, single aspect, constrained urban sites, or anywhere a planning officer has already asked the question under CC3 — [get in touch](/contact/) and we'll tell you how we'd approach the [Part O assessment](/services/part-o-overheating/) and what evidence is worth putting in front of Building Control. *Sources: [Warmest UK summer on record "increasingly likely" as temperatures stay well above average, Met Office, 11 August 2026](https://www.metoffice.gov.uk/blog/2026/warmest-uk-summer-on-record-increasingly-likely-as-temperatures-stay-well-above-average) · [The Future Homes and Buildings Standards — written statement, UK Parliament, 24 March 2026](https://questions-statements.parliament.uk/written-statements/detail/2026-03-24/hcws1445) · [Government announces full review of Overheating Regulations, Elmhurst Energy, 9 April 2026](https://www.elmhurstenergy.co.uk/blog/2026/04/09/government-announces-full-review-of-overheating-regulations-following-industry-feedback/) · [National Planning Policy Framework, August 2026 (PDF), GOV.UK](https://assets.publishing.service.gov.uk/media/6a8334c03bd75b81e2329ac4/National_Planning_Policy_Framework.pdf) — policy CC3* --- # Your drainage evidence just became a validation document URL: https://energycount.co.uk/news/nppf-2026-dm2-validation-lists-suds-statement/ Date: 2026-08-25 Every developer has a story about validation. One council wants a drainage strategy up front; the next takes the application and conditions it; a third asks for something nobody has heard of because a policy officer added it to a list in 2019. The **National Planning Policy Framework published on 17 August 2026** takes a run at that problem — and in doing so quietly moves drainage evidence forward in the programme. ## What policy DM2 says DM2 sits in the new decision-making chapter, alongside DM1 (preparing proposals) and DM3 (determining them). It has two limbs, and both matter: > "1. To ensure a clear and consistent approach to the information required to determine development proposals, local validation lists setting out the information required in support of an application for development should include the information specified in the relevant national decision-making policies (summarised in Annex C). > > 2. Local validation lists should only include additional information requirements if there is a policy in the development plan requiring a specific further assessment. Any such additional information requirements should not be applied equally to all applications but should be proportionate to the scale of development and its potential impact. Where appropriate, the requirements should clearly distinguish between what is required for major, medium and other types of development proposal." Limb 1 sets a floor. Limb 2 sets a ceiling — and it is a genuine constraint on local practice. A validation requirement that isn't in Annex C and isn't traceable to a development plan policy is now, on the face of national policy, one the council should not be applying. Blanket requirements applied equally to a 200-home scheme and a pair of semis are specifically called out. ## Annex C: what's on the national list Annex C summarises the information requirements that flow from the Framework's own decision-making policies. For anyone working on drainage, three entries matter: - a **site-specific flood risk assessment**; - a **SuDS statement** — a statement showing how the national standards have been met; - a **coastal change vulnerability assessment**, where relevant. That is the shift. A SuDS statement is not a document you produce when a condition is discharged. It is a document the application needs in order to be valid. It joins up with **policy F8**, which requires sustainable drainage on development with drainage implications to be designed in accordance with **Defra's 2025 National Standards for SuDS**. F8 tells you what the design has to comply with; DM2 and Annex C tell you that you have to show it at the front door. ## Why this changes the programme, not just the paperwork Under the old pattern, a lot of drainage work happened after permission. Outline consent came with a condition requiring a detailed drainage strategy; infiltration testing got done when the site was accessible; if the ground turned out to be worse than assumed, the layout absorbed it. Front-loading the SuDS statement breaks that sequence in a useful and an uncomfortable way at the same time. **The useful part.** Drainage constraints surface before the layout is fixed by a planning permission. If a soakaway won't work on this site, finding out at application stage costs a drawing revision. Finding out at discharge-of-conditions stage costs a redesign, a Section 73 and a delay. **The uncomfortable part.** You need real infiltration data earlier. A SuDS statement that leans on a desk-study assumption about permeability is a statement waiting to be unpicked. **BRE Digest 365** soakaway testing is not something you can do retrospectively once the layout is committed. ## What a defensible SuDS statement needs to show Nothing here is new engineering — what has changed is when it has to exist. Expect to need: - **The drainage hierarchy applied and evidenced.** Infiltration first, then discharge to a watercourse, then to a sewer — with a reason for each step you rule out. "Not feasible" without test data is not a reason. - **Infiltration testing to BRE Digest 365**, in the right locations, at the right depth, with the results and the design infiltration rate stated. If testing is genuinely not possible yet, say so explicitly and say what happens if the assumption fails. - **Compliance with the 2025 National Standards** stated against the standards themselves, not against a generic paragraph about sustainable drainage. - **Storage volumes, discharge rates and climate change allowances** shown, with the design event and the exceedance route. - **Maintenance and adoption** — who maintains what, for how long, funded how. - **Proportionality.** DM2 explicitly distinguishes major, medium and other development. A small scheme should not be asked for a major scheme's evidence pack, and you are entitled to say so. ## The other half of the policy: pushing back DM2(2) is the clause worth keeping in your back pocket. If a council's validation list asks for a document that is neither in Annex C nor required by a specific development plan policy, national policy says it should not be there. Two practical caveats before you rely on that: 1. **Local validation lists take time to catch up.** Councils will be revising them over the coming months, and the Planning Practice Guidance published alongside the Framework had topics still referring to the previous NPPF immediately after publication. Check what version you are arguing against. 2. **"Proportionate" is a judgement, not a threshold.** DM2 gives you a principle, not a number. It is a good argument at pre-application; it is a weaker argument once validation has been refused. ## What to do about it 1. **Move the soakaway testing earlier in your programme.** If the drainage strategy is now a validation document, the test results that underpin it have to exist before submission. 2. **Write the SuDS statement against the National Standards explicitly**, clause by clause. A statement that references them generally invites a request for more information — which is exactly the trigger DM3 gives an authority for pausing a decision. 3. **Be honest about assumptions.** If you are designing on an assumed infiltration rate, state it, state the sensitivity, and state the fallback. An acknowledged assumption is a far better position than one discovered later. 4. **Review the local validation list against DM2 before you accept it.** Particularly on smaller schemes, where blanket requirements are most likely to be disproportionate. 5. **Don't assume a condition will save you.** The whole direction of the new Framework is that the evidence arrives with the application. ## The bigger picture Sustainable drainage has spent years in an odd position in England: mandatory in Wales through Schedule 3, non-statutory here, and delivered through whatever the planning system could be persuaded to require. The August 2026 Framework has not commenced Schedule 3 — there is still no SuDS Approving Body in England — but it has done something with a similar practical effect. It has named the standards, required compliance with them, and made the evidence a condition of your application being accepted at all. For most developers that means one thing: the drainage engineer needs to be in the room earlier. If you have a site where infiltration is the open question — or a SuDS statement that needs to stand up at validation rather than at condition stage — [get in touch](/contact/) and we'll tell you what testing and evidence we'd want to see before it goes in. *Sources: [National Planning Policy Framework, August 2026 — policies DM2, DM3 and F8, and Annex C, GOV.UK](https://www.gov.uk/guidance/national-planning-policy-framework) · [National standards for sustainable drainage systems (SuDS), GOV.UK](https://www.gov.uk/government/publications/national-standards-for-sustainable-drainage-systems/national-standards-for-sustainable-drainage-systems-suds) · [NPPF August 2026 changes: flood risk and drainage implications for planning, Unda](https://www.unda.co.uk/news/nppf-august-2026-flood-risk-drainage-changes/)* --- # Natural England's duty to advise on planning applications has gone URL: https://energycount.co.uk/news/statutory-consultee-reform-natural-england-environment-agency/ Date: 2026-08-25 If you have ever waited eleven weeks for Natural England to comment on a nutrient budget, or watched an application stall while the Environment Agency worked through a queue, the government has just changed the rules of that game — though not in the direction most people expected. **MHCLG published its response to the "Reforms to the statutory consultee system" consultation on 17 August 2026**, the same day the new National Planning Policy Framework landed. It attracted far less attention than the NPPF, but for anyone whose schemes depend on environmental sign-off, it matters just as much. ## The headline change: Natural England no longer has to answer The most significant line in the document is easy to miss, because it is a change made by primary legislation rather than by this response: > "The Planning and Infrastructure Act 2025 amends Section 4(1) of the Natural Environment and Rural Communities (NERC) Act 2006 to remove the requirement for Natural England to provide advice on any request from LPAs relating to development under the TCPA. This will allow Natural England to prioritise its advice and focus their input on high risk and high opportunity casework." That is a real shift. Natural England will still respond where the law separately requires it — the Town and Country Planning (Development Management Procedure) Order still prescribes it as a consultee on certain applications — but the open-ended duty to advise whenever an authority asks is gone. What replaces it is a **prioritisation framework**, to be set out in an **Operational Statement** produced with Defra. That document is not published yet. The response says only that it is "proposed to be in place shortly", and adds: > "Until the Operational Statement is published, Natural England's existing approach to dealing with planning casework continues to apply." So there is a live gap: the duty has been removed, but the replacement rules for what Natural England will and won't look at have not been written down. If you are relying on Natural England advice for a nutrient neutrality case, that Operational Statement is the document to watch. ## The Environment Agency: no change to criteria, but explicit triage The response makes no change to when the Environment Agency must be consulted. What it does confirm is that the Agency intends to ration its own effort: > "The Environment Agency is committed to effective triaging to ensure efficiency of responses whilst ensuring environmental protection and sustainable development by focussing resource on more complex casework. This includes recruiting and training staff, improving guidance, developing new case management systems, data standards, alongside utilising Artificial Intelligence (AI) to triage and process casework, and enhanced geospatial tools to support users." Respondents were blunt about the risk. The response records "strong cross-sector consensus that complex environmental risks, including flooding, water quality, hydrology, contaminated land and cumulative ecological impacts, require specialist scrutiny", and warns that "reframing objections as 'advice' or relying too heavily on standing advice could weaken safeguards". Money is going in alongside the triage: **£100 million** to modernise the environmental planning services of Natural England, the Environment Agency and the Forestry Commission, plus a Defra **Lead Environmental Regulator** model being piloted on eight major projects to stop developers receiving conflicting advice from different Defra bodies. ## The bit that bites: NPPF policy DM3 None of the above would matter much if authorities simply waited for the advice anyway. The new NPPF closes that door. Policy **DM3(1)(d)** tells local planning authorities to: > "Consult statutory or internal consultees only where it is necessary to do so. Decisions on development proposals should not be delayed in order to secure advice from a statutory or internal consultee beyond their statutory deadlines unless there is insufficient information to make the decision, there are public safety risks from proceeding without advice, or more detailed advice may enable an approval rather than a refusal" Read that alongside the consultee reforms and the direction is clear. Consultees will comment on less; authorities are told not to wait; and the exception that keeps the door open is **"insufficient information to make the decision"**. That exception is the whole ballgame. If your submission is thin, the authority now has a named national policy reason to pause. If your submission is complete, the same policy pushes them to decide. ## What else the response confirms - **No further removals.** "At this stage, we are not proposing to remove any additional statutory consultees", and the moratorium on creating new ones stays. - **The Gardens Trust and Theatres Trust lose statutory consultee status**, replaced by notification duties. **Sport England is retained** but with a narrowed list of referral triggers — the government expects its referrals to "fall by half or more" from around 1,100 applications a year. - **The Mining Remediation Authority will stop routinely commenting on discharge of conditions** — worth knowing if you work on coalfield sites, where MRA comments at condition stage have been a familiar delay. - **Water companies will not become statutory consultees on planning applications.** The government's position is that "strategic issues, such as water capacity, drainage, and wastewater management are best dealt with at a strategic level" — through plan-making, "Requirement to Assist" regulations and the forthcoming Clean Water Bill. If wastewater headroom is your constraint, the fight has been moved to the local plan. - **A wider aim to trim advice.** The ministerial foreword states the government "will also take forward changes to reduce the scope of advice provided by some of the largest statutory consultees." ## Timing There is no commencement date. The foreword says only that "regulations will follow in due course to bring these reforms into force", with Planning Advisory Service support for authorities. A further consultation is promised on a **planning fee surcharge** to fund key statutory consultees. The NPPF policies, by contrast, apply to decisions **now**. ## What to do about it 1. **Stop treating consultee advice as a design service.** The clear policy direction is that consultees respond to complete, well-evidenced submissions rather than helping you work out what the answer should be. Bring the assessment to them, not the question. 2. **Front-load the technical evidence.** Nutrient budgets, drainage strategies, infiltration testing, contamination assessments — anything that would previously have been left to a condition is now the thing that decides whether "insufficient information" applies to your application. 3. **Watch for Natural England's Operational Statement.** It will tell you which categories of case still get individual advice and which fall to standing advice. Until it appears, existing practice continues — so cases submitted in this window sit in an unusually uncertain space. 4. **Check whether your nutrient mitigation route depends on Natural England capacity.** Credit-based schemes and bespoke on-site mitigation carry different exposure to a consultee that is being told to prioritise. 5. **If wastewater capacity is the constraint, engage at plan-making stage.** The response is explicit that this is where the government wants the issue resolved. ## The bigger picture This is deregulation of process rather than of standards. The Habitats Regulations still apply. Nutrient neutrality obligations still apply. Flood risk policy has just been strengthened, not weakened, in the new NPPF. What has changed is who does the thinking — and the answer is increasingly the applicant, not the regulator. For schemes in nutrient-affected catchments that is a meaningful shift. A nutrient budget that would once have been iterated with Natural England now needs to be right when it is submitted. If you have a scheme in a nutrient catchment and want the budget checked before it goes in — or you would like a second opinion on mitigation that was calculated some time ago — [get in touch](/contact/) and we'll tell you how we'd approach it. *Sources: [Reforms to the statutory consultee system: government response, GOV.UK, 17 August 2026](https://www.gov.uk/government/consultations/reforms-to-the-statutory-consultee-system/outcome/reforms-to-the-statutory-consultee-system-government-response) · [National Planning Policy Framework, August 2026 — policy DM3, GOV.UK](https://www.gov.uk/guidance/national-planning-policy-framework) · [The government publishes its response to the consultation relating to statutory consultees, The Planning Jungle, 18 August 2026](https://planningjungle.com/2026/08/18/the-government-publishes-its-response-to-the-consultation-until-13-01-2025-relating-to-statutory-consultees/)* --- # Half of England's councils failed the Housing Delivery Test — what the 2025 results mean URL: https://energycount.co.uk/news/housing-delivery-test-2025-results/ Date: 2026-08-24 Buried in the noise of NPPF week was a data release with real consequences for where the next few years of housing schemes will come forward. On **17 August 2026**, MHCLG published the **2024 and 2025 Housing Delivery Test (HDT) measurements** — two years at once, after a delay, to bring the test back up to date and re-establish the annual cycle. The **2025 measurement is the current one** for decision-making, and the Chief Planner's newsletter directs authorities to use it. ## What the test measures The HDT is the government's backward-looking check on delivery: net homes actually completed in an authority's area over a rolling three-year period — for the 2025 measurement, **2022/23 to 2024/25** — divided by the homes required, published as a percentage. It measures completions, not permissions. An authority can be granting consents freely and still fail if the homes aren't getting built. It's the counterpart to the forward-looking **five-year housing land supply**: one asks whether homes were delivered, the other whether enough deliverable sites exist for the next five years. Either can now expose an authority to national policy consequences. ## The 2025 numbers Of **301 authorities with a numerical result** (the Isles of Scilly has none): - **147 — nearly half — scored below 95%**, triggering at least the requirement to publish an action plan; - **35** sat between 85% and 94%; - **19** sat between 75% and 84%, where a **20% buffer** is added to the authority's housing land supply requirement; and - **93 — almost a third of England's planning authorities — scored below 75%**, the most serious threshold. The remaining 154 authorities (just over half) reached 95% or above. ## The 75% line now works differently Under the pre-2026 framework, a sub-75% HDT result switched on the old paragraph 11 "tilted balance". The **August 2026 NPPF rewires this**: a score below 75% now counts as **evidenced unmet housing need** for the purposes of policy **S5(1)(j)**, feeding the restructured **S3–S6 presumption in favour of sustainable development**. For a suitable housing scheme outside a settlement in a sub-75% district, that evidence can bring the proposal within the favourable S5 policy category — and the same unmet-need evidence is relevant to the grey-belt route in Green Belt authorities. In plain terms: in the 93 districts below the line, the policy case for housing on suitable unallocated sites just got materially stronger, and refusals in those places will be harder to defend at appeal. A low score doesn't override design, highways, heritage, flood risk or Green Belt policy — but it changes the starting point. The **HDT Rule Book was also updated on 17 August** to reflect unmet-need adjustments to local housing need and transitional arrangements for the revised standard method, and those changes were applied to both new measurements. ## What this means if you build — or assess — new homes Expect activity to cluster where the test was failed. Promoters will move on sites in sub-75% districts while the evidence is fresh; authorities under the 20% buffer will be looking to grant permissions that shore up their supply; and appeal decisions over the next year will show how inspectors handle the new S5 mechanics. The 2025 results are the current measurement until the next annual release. For assessors and housebuilders, the timing matters. Schemes unlocked by these results will be designed and submitted straight into the [Future Homes Standard transition](/news/future-homes-standard-transitional-deadline-commencement/) — building regulations applications from 24 March 2027 will be under the FHS, with SAP 10.3 as the compliance methodology at launch. A site that gets its planning permission because of a weak HDT score still has to get through Part L, and under the FHS notional dwelling the fabric and bridging detail will be doing more of the work than ever. If you've got schemes coming forward — especially in a sub-75% district where the planning window has just opened — [get in touch](/contact/) about your Part L and SAP 10.3 strategy early. Bespoke thermal-bridging PSI values instead of punitive defaults remain one of the cheapest compliance margins available, and that's exactly what **ΨMonkey** and our assessor team are for. *Sources: [Housing Delivery Test: 2025 measurement, MHCLG, GOV.UK](https://www.gov.uk/government/publications/housing-delivery-test-2025-measurement) · [Housing Delivery Test: 2024 measurement, MHCLG, GOV.UK](https://www.gov.uk/government/publications/housing-delivery-test-2024-measurement) · [Housing Delivery Test measurement rule book, GOV.UK](https://www.gov.uk/government/publications/housing-delivery-test-measurement-rule-book) · [Housing Delivery Test results 2024 and 2025 published, Planning Geek, 17 August 2026](https://www.planninggeek.co.uk/2026/housing-delivery-test-results-2025/) · [Planning Update Newsletter, 18 August 2026 — Letter from MHCLG to Chief Planning Officers, GOV.UK](https://www.gov.uk/guidance/planning-guidance-letters-to-chief-planning-officers)* --- # Your SuDS strategy now has a standard form — national templates published URL: https://energycount.co.uk/news/suds-strategy-templates-august-2026/ Date: 2026-08-24 A week after the new NPPF made Defra's National Standards the named rulebook for sustainable drainage, the paperwork has caught up. Tucked into the **Chief Planner's Planning Update Newsletter of 18 August 2026** is a practical announcement that will touch almost every planning application with drainage implications: the **Environment Agency has published national SuDS Strategy Templates**, produced with **CIRIA, the Association of SuDS Authorities (ASA), Arup** and a working group of SuDS practitioners. The stated aim is disarmingly simple: help applicants "submit the right information on SuDS first time", and make it easier for local planning authorities and Lead Local Flood Authorities to check whether a proposed drainage system has been designed in accordance with **Defra's National Standards for sustainable drainage systems**. ## Two templates, picked by scale To reflect the proportionate approach in the new National Planning Policy Framework, there are two versions: - a **SuDS Strategy Template for Major Development** — broadly, schemes of 10 or more homes or the non-residential equivalent; and - a **SuDS Strategy Template for Non-major Development** — everything smaller, where a full major-scheme strategy would be overkill. Applicants are told to pick the template that best fits the scale of the proposal, and to download it fresh each time from the **Planning Portal or the CIRIA website** so they're always working from the latest iteration rather than a saved copy. ## Why this matters more than it sounds Templates are rarely news. This one is, for two reasons. First, the **Environment Agency is explicitly encouraging LPAs and LLFAs to adopt the national templates** and drop locally produced versions. Anyone who submits drainage strategies across several authorities knows the current reality: each LLFA has its own pro-forma, its own appetite for detail and its own pet requirements. A single national format — like the standardised decision-making policies in the new NPPF — is aimed at squeezing out exactly that local variation. Second, a standard form cuts both ways. It tells you precisely what to include, and it makes what's missing impossible to hide. Expect the template to walk through the things the National Standards already ask for: where your site sits on the **discharge hierarchy** (reuse, then infiltration, then a watercourse, then a surface water sewer, with a combined sewer strictly last), the evidence behind that choice, runoff rates, storage volumes, the treatment train and the maintenance arrangements. A drainage strategy that asserts "infiltration is not viable" without percolation test results to show for it is going to look thin in a box that asks for the data. For anyone sizing soakaways, that means the familiar routine — trial pits and infiltration testing to **BRE Digest 365**, storage checked across a range of storm durations at the design return period with a climate change uplift — is no longer just good practice. It's the evidence the checking officer's form now expects to see, in the place they expect to see it. ## Free SuDS training for planners Alongside the templates, the Environment Agency and the **Town and Country Planning Association** have launched a free, interactive e-learning module on securing good SuDS through planning, developed with experts from ASA and with input from CIRIA and CIWEM. It's aimed at planners and flood-risk practitioners, self-paced, and [open to anyone to register](https://learning.tcpa.org.uk/courses/intro-suds-for-planners). If the person determining your application has just done a course on what a compliant SuDS strategy looks like, it's worth knowing what they were taught. ## The bigger picture This lands as part of a deliberate sequence. The [August 2026 NPPF's policy F8](/news/nppf-2026-suds-national-standards-policy-f8/) requires SuDS on all development with drainage implications to be designed in accordance with the National Standards; Schedule 3 of the Flood and Water Management Act stays uncommenced, with the government betting instead on this strengthened planning-led approach. Named standards, a national submission format, trained checking officers — the direction is consistent, and it all points to drainage strategies being marked against a rubric rather than negotiated case by case. The practical advice is unchanged but sharper: **test early, and test properly**. An infiltration rate assumed at layout stage and disproved at discharge-of-conditions stage still means a redesign — only now the gap will be visible on a standard form at validation rather than surfacing quietly later. **SoakMonkey** runs the BRE Digest 365 soakaway method in your browser — infiltration rate from your percolation results, storage sizing tested across storm durations, and a Building Control-ready report to drop straight into your SuDS strategy. Sizing on screen is free; the PDF export is £25 +VAT (£30 inc VAT). [Try SoakMonkey →](/tools/soakaway-calculator/) And if a planning condition is asking for a SuDS strategy to the National Standards and you're not sure how your site will behave, [get in touch](/contact/) — a trial pit and an hour of sizing usually settles it. *Sources: [Planning Update Newsletter, 18 August 2026 — Letter from MHCLG to Chief Planning Officers, GOV.UK](https://www.gov.uk/guidance/planning-guidance-letters-to-chief-planning-officers) · [National standards for sustainable drainage systems (SuDS), Defra, GOV.UK](https://www.gov.uk/government/publications/national-standards-for-sustainable-drainage-systems/national-standards-for-sustainable-drainage-systems-suds) · [Introduction to SuDS for Planners (free e-learning), TCPA](https://learning.tcpa.org.uk/courses/intro-suds-for-planners)* --- # The EPC accuracy audit: homes use less energy than the model says URL: https://energycount.co.uk/news/epc-accuracy-research-performance-gap/ Date: 2026-08-23 If you lodge EPCs for a living, there's a government research report you should know about — because it quantifies, home by home and month by month, how far the modelled numbers drift from what the meter actually records. The **EPC accuracy research**, published by DESNZ on **26 May 2026** and produced by the **UCL Energy Institute with Alan Pither Limited**, compared EPC-modelled energy use against smart-meter and temperature data from **over 1,100 homes**. It was commissioned to feed the EPC Action Plan and the development of the **Home Energy Model** — which makes it, in effect, the evidence base the next methodology will be judged against. It didn't make much noise when it landed, but with HEM held back for final assurance, it's exactly the kind of evidence being pored over right now. ## The headline numbers On average, **gas-heated homes used 16.0% less energy than their EPC models predicted**. Electrically heated homes showed a much bigger gap: **31.4% less** on average, peaking at **47% in December** — midwinter homes using barely half the energy the model says they should. The 16% figure isn't fixed, and the way it shrinks is telling. When the researchers rebuilt each model with the current RdSAP version, the actual weather during monitoring, the occupants' real heating patterns and any improvements installed since the certificate was lodged, the gas gap narrowed to **10.9%**. More than half of that correction came from a single source: work done to the home *after* the EPC was issued. The biggest "inaccuracy" in the EPC stock isn't the calculation — it's certificates that no longer describe the building. For homes whose boiler had been replaced since lodgement, updating the model shrank the gap from 22.1% to 9.5%. ## Where the model drifts Because the study broke energy use down by fuel and season rather than comparing annual totals, it could spot offsetting errors that headline figures hide: - **Homes are warmer than SAP assumes.** Measured internal temperatures ran above modelled ones, even in band F and G homes — so underheating can't explain the gap. The data also gave little support to SAP's two-zone assumption that the non-living area sits up to 3°C cooler; in practice the zones track each other closely. - **Ventilation defaults inflate heating demand.** RdSAP 2012 assumes an average heating-season air change rate of 1.02 ach for F and G rated homes against 0.69 for A and B. Field measurements suggest real rates are often lower — sometimes below SAP's 0.5 ach minimum, which the report recommends reviewing for both SAP and HEM. - **Solar gains are underpredicted — by up to 54%.** April 2021, the sunniest April on record, acted as a natural experiment, and RdSAP underpredicted the effect of passive solar heating by 54% against monitored data. Age-band glazing assumptions are a suspected culprit; RdSAP 10's measured glazing should close part of the gap. - **The summer fuel split is wrong.** Total summer delivered energy comes out almost exactly right, but metered summer gas use is 34% higher than modelled while electricity use in gas-heated homes runs 18.2% lower year-round. The errors cancel in a delivered-energy metric — but not in a cost or primary-energy metric. ## The new-build sting One finding runs against the grain of everything above, and it's the one that matters most for our corner of the industry: **older homes outperform their models, but new homes underperform theirs**. In the existing stock, age-based fabric defaults are pessimistic — real walls, roofs and floors lose less heat than assumed. In new builds the gap reverses: **measured heat loss is higher than modelled**, consistent with every as-built performance study of the last decade. Design-stage assumptions about fabric, junctions and airtightness are flattering what's actually delivered on site — which is precisely the gap the FHS's tighter fabric standards, mandatory testing culture and (eventually) HEM's half-hourly engine are meant to squeeze. There's a second new-build wrinkle: homes assessed as built with full SAP get a *worse* EPC when they're later reassessed for sale under RdSAP, because the reduced-data procedure falls back on defaults in place of construction data that existed all along. The report's fix is sensible — give RdSAP assessors access to the original as-built SAP calculation for any home built since 2008. ## What it means for HEM and reformed EPCs Four modelling assumptions are flagged for review in HEM as well as SAP: the two-zone heating assumption, seasonal electricity demand, the heat transfer coefficient assumptions, and the 0.5 ach ventilation minimum. The study also demonstrates that smart-meter energy signatures can validate a model version against measured reality — including half-hourly models, which is exactly what HEM produces. SAP ran for three decades without a standing accuracy audit; HEM could launch with one built in. Two recommendations read as direct endorsements of the reform direction: drop primary energy as a headline certificate metric, and make EPCs dynamic — updated automatically when regulated work like a boiler swap is recorded, rather than frozen for ten years. That lines up with the [four-metric reformed EPC](/news/reformed-epcs-four-metrics-home-energy-model/) due in the second half of 2027, and with the measured-performance direction set out in the [SMETER Strategic Guide](/news/smeter-strategic-guide-measured-performance/). ## What to do with this For assessors, the direction of travel is unmistakable: modelled assessments are heading into an era where they'll be routinely checked against metered reality. The practical response is the same one we'd give for any compliance model — get the inputs right. Assessor error alone shifted predicted space and water heating by 6% on average in the resurveyed subsample, mostly through misrecorded dimensions, heating systems and wall insulation. And on the new-build side, the finding that as-built heat loss exceeds the model is a reminder that default junction values and optimistic PSI assumptions are exactly where paper performance leaks away. If you'd rather your junctions were calculated than assumed, that's our patch — modelled PSI values that stand up when someone eventually puts a meter on the result. [Get in touch](/contact/) and we'll tell you how we'd approach your scheme. *Sources: [Energy Performance Certificate (EPC) accuracy research, DESNZ, 26 May 2026](https://www.gov.uk/government/publications/energy-performance-certificate-epc-accuracy-research) · [EPCs Overestimate Energy Use by 16%: What the Government's Accuracy Research Found, HEM Guide](https://home-energy-model.co.uk/news/2026-07-15-epc-accuracy-research/)* --- # Stodmarsh movement: Stour nutrient credits are now on sale URL: https://energycount.co.uk/news/stour-nutrient-credits-stodmarsh/ Date: 2026-08-23 If you've got a scheme stuck in east Kent, this is the one to read. **Stour Environmental Credits (SEC)** — the not-for-profit company owned and overseen by **Ashford Borough Council and Canterbury City Council** — announced on **30 July 2026** that it has begun issuing **nutrient credits** for the Stour catchment. That gives developers in one of the country's most prominent stalled catchments a locally run, council-backed route to demonstrate nutrient neutrality and get planning permissions over the line. ## What's actually on offer SEC's initial mitigation programme is expected to support the delivery of **more than 1,500 new homes** across the catchment. Credits are being released in tranches rather than all at once: the **first release enables up to 30 dwellings** to progress, with further releases to follow "on a regular basis" as existing mitigation schemes progress and new projects come forward. Credits are generated from verified local mitigation projects that reduce nutrient pollution in line with Natural England guidance, and the scheme sits alongside Kent County Council's Stodmarsh Catchment Nutrient Mitigation Strategy. Because SEC is a not-for-profit, the proceeds are recycled — into buying more mitigation, developing new schemes, and monitoring the existing mitigation in perpetuity. Pricing and a register-your-interest form are on the [SEC website](https://www.stourenvironmentalcredits.co.uk/). ## Why Stodmarsh matters The **Stodmarsh SAC/SPA/Ramsar** near Canterbury is the protected site behind one of the largest nutrient neutrality blockages in England — advice that has held up thousands of homes across the Stour valley, taking in Canterbury, Ashford and neighbouring districts. And it's a **dual-nutrient catchment**: schemes have to be neutral for **both nitrogen and phosphorus**, which means a compliant scheme needs a credit position for each, not just one headline number. That's worth dwelling on before you pick up the phone. A tranche of credits is only useful once you know what your scheme actually needs — and that starts with the **nutrient budget**: occupancy, water use, wastewater treatment works, land-use change, the lot. With credits being drip-fed in releases, schemes that arrive with a calculated budget and a clear credit requirement will be the ones best placed to secure an allocation early. ## The bigger picture: local schemes still carry the load The strategic fix for nutrient neutrality — the **Nature Restoration Fund**, with Natural England preparing **Environmental Delivery Plans** so developers can discharge nutrient obligations through a single levy payment — [took its first legal steps in June](/news/nature-restoration-fund-nutrient-regulations-laid/). But the first EDPs are still being prepared, with each draft facing a 28-day public consultation before it can be approved; officials have indicated the first will launch by the end of 2026. Until an approved EDP covers your catchment, site-by-site neutrality remains the law, and locally led credit schemes like SEC are what's actually keeping consents moving. For assessors and consultants, that makes the current period a hybrid one: keep calculating budgets and securing mitigation under the existing rules, while watching where the first EDPs land — Natural England notified 23 planned EDPs back in December 2025, 16 of them for nutrients. ## What to do about it If you're promoting a scheme in the Stour catchment: run the nutrient budget now, work out your nitrogen and phosphorus credit requirement, and register your interest with SEC early — the first release is small, and allocation will favour schemes that know their numbers. NutrientMonkey covers the Stodmarsh catchment, so you can get an instant first-pass budget for your site before committing to anything. Want the full calculation done properly, ready for validation? [Send us the details](/contact/) and we'll take it from there. *Sources: [Stour Environmental Credits begin selling nutrient credits, Ashford Borough Council, 30 July 2026](https://www.ashford.gov.uk/news/latest-news/stour-environmental-credits-begin-selling-nutrient-credits-and-opening-building-opportunities-in-the-stour-catchment/) · [Stour Environmental Credits](https://www.stourenvironmentalcredits.co.uk/) · [Natural England will 'launch' first EDP by the end of year, Planning Resource](https://www.planningresource.co.uk/article/1960547/natural-england-will-launch-first-edp-end-year-official-reveals)* --- # Overheating is now a named planning policy — not just a Part O problem URL: https://energycount.co.uk/news/nppf-2026-overheating-policy-cc3/ Date: 2026-08-22 Overheating has been a Building Regulations problem since Approved Document O landed in 2021. You design the home, you run the simplified method or a TM59 dynamic model, you hand the results to Building Control, and planning barely touches it. The **National Planning Policy Framework published on 17 August 2026** changes where that conversation starts. Overheating was not absent from the previous Framework — the December 2024 version mentioned it in its general climate framing (paragraph 161) and in its plan-making paragraph on long-term risks (162). What it did not have was a decision-making policy telling applicants to design for it. The 2026 rewrite does. ## What the new policies actually say The Framework's climate chapter contains three coded policies, **CC1 to CC3**. Two of them mention overheating directly. **CC1** is the plan-making policy. It requires development plans to take a proactive approach to adapting to climate change, "taking into account the implications of extreme weather and long-term climate trends including **overheating**, wildfires, drought, flood risk, coastal change, water supply, biodiversity and landscapes." **CC3** is the national decision-making policy on adaptation, and it is the one that will show up on your desk. It requires development proposals to take account of the current and potential impacts of climate change over the lifetime of the scheme and, where relevant, to: > "Use design approaches which minimise risks from overheating in accordance with policy DP3(2)(b), and include green infrastructure and suitable tree planting in accordance with policies DP3(2)(c) and N3" Two things follow from that wording. First, overheating sits alongside flood risk, coastal change and SuDS in the same list — the company it keeps tells you how seriously it is meant to be taken. Second, it routes through **DP3**, the design policy in the well-designed places chapter, which means overheating is being framed as a design-quality issue rather than a bolt-on calculation. ## Why this matters now Because the Building Regulations side has not caught up. **Approved Document O (2021)** remains in force and still references the **2017** edition of CIBSE TM59. The government confirmed in its Future Homes and Buildings Standards consultation response on **24 March 2026** that Part O would not be amended alongside Parts L and F, and would instead get its own standalone technical review — covering, among other things, adoption of the updated TM59 methodology, fixes to the simplified method, noise and security guidance, extension to material change of use, and updated weather files. Meanwhile **CIBSE published TM59:2026** in July 2026, a substantial rewrite of the methodology that Part O does not yet point to. So the sequence is now: planning policy names overheating in August 2026; the industry methodology was rewritten in July 2026; and the Approved Document that governs compliance still references a 2017 document. That gap is where arguments happen. ## What it means in practice Nothing here creates a new numerical standard. CC3 does not set a temperature threshold, and it does not require a TM59 model. What it does is give a local planning authority a clear, named national policy hook to ask how a scheme deals with overheating — at application stage, before Building Control ever sees it. Expect that to surface as: - **Validation and consultee questions** on larger or higher-risk schemes — single-aspect flats, high glazing ratios, urban sites where opening windows is constrained by noise or air quality. - **Design-and-access or sustainability statements** being expected to say something specific about overheating strategy, rather than deferring it to "Part O at technical design". - **Planning conditions** requiring an overheating assessment or a mitigation strategy to be submitted and approved. Once that condition exists, the assessment method and the acceptance criteria become negotiable in a way they are not under Part O. - **Tension between policies.** CC3's answer to overheating is passive design, shading and green infrastructure — which can pull against glazing, daylight, density and elevational treatment expectations elsewhere in the Framework. Conflicts between Part O and other parts of the Building Regulations are one of the workstreams in the government's own Part O review, so this is a known problem rather than a theoretical one. The NPPF does not resolve it for you. ## What to do about it If you are working on schemes going into planning now: 1. **Do the overheating thinking at concept stage, not at Building Regs stage.** Orientation, glazing ratio, aspect and shading are cheap to change on a layout drawing and expensive to change once the planning permission fixes the elevations. 2. **Be explicit in the planning submission.** A short, honest paragraph on the overheating strategy — passive measures first, what you have assumed about openable windows, what you would do if the dynamic model came back tight — is much easier than answering it cold after a consultee objection. 3. **Watch which TM59 you are being asked for.** Approved Document O still means the 2017 edition. A planning condition drafted loosely as "in accordance with CIBSE TM59" now arguably means the 2026 edition, which is a different test with different criteria. Get that pinned down in the wording rather than discovering it at discharge. 4. **Do not assume Part O compliance settles the planning question.** It usually will. But CC3 is drafted around risk and design approach, not around a compliance certificate, so a scheme that scrapes through the simplified method may still attract questions. ## The bigger picture This is a familiar pattern. Water efficiency and sustainable drainage both moved from technical guidance into named planning policy before the Building Regulations changed, and both ended up being fought over at application stage. Overheating now looks set to follow the same route — with the added complication that the review of Part O is still open, so the technical standard the planning system is implicitly reaching for has not yet been written. If you have a scheme where overheating is likely to be the awkward bit — flats, constrained urban sites, high glazing, or anywhere a planning officer has already asked the question — [get in touch](/contact/) and we'll tell you how we'd approach the assessment and what evidence is worth putting in front of the planners. *Sources: [National Planning Policy Framework, August 2026 (PDF), GOV.UK](https://assets.publishing.service.gov.uk/media/6a8334c03bd75b81e2329ac4/National_Planning_Policy_Framework.pdf) — chapter 5, policies CC1–CC3 · [The Future Homes and Buildings Standards — written statement, UK Parliament, 24 March 2026](https://questions-statements.parliament.uk/written-statements/detail/2026-03-24/hcws1445) · [Future Homes and Buildings Standards consultation response (PDF), GOV.UK](https://assets.publishing.service.gov.uk/media/69c13592bb0dfe55b83e4b85/Future_Homes_and_Buildings_Standards_Consultation_Response.pdf) · [Government announces full review of Overheating Regulations, Elmhurst Energy, 9 April 2026](https://www.elmhurstenergy.co.uk/blog/2026/04/09/government-announces-full-review-of-overheating-regulations-following-industry-feedback/)* --- # Retrofit just got a stronger planning policy — 'substantial weight' under CC2 and CC3 URL: https://energycount.co.uk/news/nppf-2026-substantial-weight-existing-buildings/ Date: 2026-08-22 Most of the attention on the **17 August 2026 National Planning Policy Framework** has gone to housing numbers, stations and the rewritten flood risk chapter. There is a smaller change in the climate chapter that matters if you ever put a heat pump, solar array or fabric upgrade in front of a planning officer. ## The change The December 2024 Framework said this, at paragraph 167: > "Local planning authorities should also give **significant weight** to the need to support energy efficiency and low carbon heating improvements to existing buildings, both domestic and non-domestic (including through installation of heat pumps and solar panels where these do not already benefit from permitted development rights)." The August 2026 Framework says this, at policy **CC2(2)**: > "**Substantial weight** should be given to the benefits of improving the energy efficiency of existing buildings and/or drawing energy from district heat networks, renewable and low carbon sources (including through the installation of heat pumps and solar panels where these do not already benefit from permitted development rights) **where this would be achieved through proposals for development**." Three differences are worth pulling out. **Significant became substantial.** Planning weight is not a formally defined scale, and lawyers will argue about whether "substantial" genuinely sits above "significant". But it is not accidental drafting — the Framework uses "substantial weight" deliberately and repeatedly across its new decision-making policies, and a decision-maker now has to explain why a benefit given substantial weight by national policy was outweighed. **The benefit is the thing weighed, not the need.** The old wording weighed "the need to support" improvements. The new wording weighs "the benefits of improving". That is a subtle shift from a policy aspiration to a material planning benefit sitting on the balance. **There is a new limiting clause.** "Where this would be achieved through proposals for development" scopes the policy to what the application actually delivers. It is not a free-floating credit for being an energy-conscious applicant; the efficiency or low-carbon gain has to be part of the scheme in front of the authority. ## And a new one for resilience Policy **CC3(2)** adds a parallel provision that has no real predecessor: > "Substantial weight should be given to the benefits of improving the resilience of existing buildings and public spaces to anticipated climate change impacts where this would be achieved through proposals for development." So adaptation work — shading, ventilation strategy, surface water management, cooling resilience — now attracts the same policy weight as carbon reduction when it is delivered on existing stock. That is new, and it is likely to be useful in exactly the cases where retrofit and heritage collide. ## Where this actually bites Permitted development rights already cover a large share of domestic heat pumps and solar, and the **GPDO amendment coming into force on 27 August 2026** rewrites and broadens the rights for domestic solar specifically. This policy is aimed at everything that falls outside those rights: - **Conservation areas and listed buildings**, where external wall insulation, glazing replacement, solar panels and air source heat pumps routinely need consent. CC2(2) does not override the heritage policies — the Framework's heritage chapter still applies — but it strengthens the public-benefit side of the balancing exercise. - **Flats and mixed-use buildings**, where permitted development rights are narrower or absent. - **Non-domestic retrofit**, which is explicitly in scope and is going to matter more as MEES tightens. - **Larger schemes with a refurbishment component**, where fabric upgrades to retained buildings can now be presented as a weighted planning benefit rather than a neutral fact. ## What to do about it The practical move is to stop treating the energy performance improvement as background detail in a planning submission and start presenting it as a benefit, with numbers. - **Quantify it.** "Improves the fabric" is weak. A modelled reduction in heat demand, a before-and-after U-value schedule, an estimated bill saving or an EPC uplift is something a case officer can put on the balance and defend in a report. - **Cite the policy by name.** CC2(2) for efficiency and low-carbon heat; CC3(2) for resilience. Coded policies are easier for officers to reference than paragraph numbers, which is rather the point of the rewrite. - **Show it is delivered by the development.** Given the new limiting clause, make the link explicit between the works applied for and the performance gain claimed. - **In heritage cases, do the balance for them.** Set out the harm, set out the public benefit, and note that national policy requires substantial weight on the benefit side. That is a considerably better position than it was under paragraph 167. None of this makes a bad application good. But if you have been losing marginal retrofit and low-carbon-heat applications on the balance, the balance has just moved. If you need the performance side of a retrofit or refurbishment quantified properly — fabric modelling, U-values, thermal bridging and the evidence to back a planning statement — [get in touch](/contact/) and we'll tell you what we'd put together. *Sources: [National Planning Policy Framework, August 2026 (PDF), GOV.UK](https://assets.publishing.service.gov.uk/media/6a8334c03bd75b81e2329ac4/National_Planning_Policy_Framework.pdf) — chapter 5, policies CC2 and CC3 · [National Planning Policy Framework (December 2024), chapter 14, paragraph 167, GOV.UK](https://www.gov.uk/guidance/national-planning-policy-framework/14-meeting-the-challenge-of-climate-change-flooding-and-coastal-change) · [National Planning Policy Framework guidance page, MHCLG, 17 August 2026](https://www.gov.uk/guidance/national-planning-policy-framework)* --- # The NPPF now has a chapter about the pipes and the grid URL: https://energycount.co.uk/news/nppf-2026-clean-energy-and-water-w1-w4/ Date: 2026-08-21 Ask most developers what actually stops a site, and the answer is rarely design. It's a grid connection date, or a treatment works with no headroom, or a catchment where the nutrient position hasn't moved in three years. The **National Planning Policy Framework published on 17 August 2026** gives those problems their own chapter for the first time. **Chapter 10, "Securing clean energy and water"**, contains four policies — two for plan-making, two for decisions — and its stated objective is to support energy and water infrastructure "in ways which align with wider development, clean power and net zero objectives". ## W1: capacity has to be understood before growth is located The plan-making policy is the substantive one. **W1** requires the development plan to be informed by **early engagement between the plan-making authority, utility providers, regulators and network operators**, so there is a clear understanding of: - energy supply and network capacity - water supply, drainage and **wastewater capacity** - the additional infrastructure provision those imply That engagement has to consider planned growth, changing consumption patterns and climate change, and must draw on the relevant strategic infrastructure plans — Water Resource Management Plans, Drainage and Wastewater Management Plans, and, once published, the Strategic Spatial Energy Plan, Centralised Strategic Network Plan and Regional Energy Strategic Plans. The plan then has to reflect it by taking those factors into account **in the location and phasing of planned growth**, making provision for the new or enhanced infrastructure needed, and setting out measures to stop neighbouring development constraining the operation or future expansion of existing networks. That last limb is quietly useful. Sites near a treatment works or a substation have historically been allocated without much thought about whether the allocation forecloses the operator's expansion land. W1 asks plans to think about it. ## W2 and W3: the energy side **W2** asks plans to identify areas suitable for renewable and low carbon energy development and electricity network infrastructure — including for **re-powering and life extension** of existing sites — and to identify opportunities for development to draw heat or energy from decentralised networks such as district heat networks. **W3** is the decision-making counterpart. Substantial weight goes to the benefits of energy security, economic development and the net zero transition; to the additional benefit of re-using an established site for re-powering; and to the contribution of small-scale and community-led projects. Crucially: > "Applicants should not be required to demonstrate the need for renewable or low carbon energy development and electricity network infrastructure." Where time-limited development is proposed, applications should come with decommissioning and site restoration proposals. ## W4: water infrastructure gets the same treatment **W4** mirrors W3 for water. In considering proposals for water supply, drainage and wastewater development, substantial weight should be given to the benefits of: - providing the capacity needed to serve proposed development, and/or improving security of supply and capacity for existing users, and - **improving water quality and reducing water-borne pollution** And again: applicants should not be required to demonstrate the need for water infrastructure developments. ## Why this matters if you work in a nutrient catchment The wording of W4(1)(b) is the bit to notice. Improving water quality and reducing water-borne pollution now attracts substantial weight in its own right — which is the same problem nutrient neutrality has been solving one housing site at a time since 2018. None of this changes the Habitats Regulations. A scheme in a protected catchment still needs its nutrient budget and its mitigation, and the Nature Restoration Fund route is still being built out through Environmental Delivery Plans. But the planning framework is now more clearly on the side of the treatment works upgrade or the wetland scheme that fixes the catchment rather than mitigating around it — and W1 pushes catchment constraints into plan-making, where they belong, rather than leaving every applicant to discover them individually. For solar, W2 and W3 sit alongside the **Future Homes Standard's requirement L3** for on-site renewable electricity generation and the [new permitted development rights for domestic solar](/news/gpdo-solar-permitted-development-27-august-2026/) that take effect on 27 August. The direction is consistent: generation and network capacity are being treated as things the planning system should be actively enabling, not merely tolerating. ## What we'd suggest doing Two practical points. **Check the catchment before the offer, not after.** A nutrient budget is a short piece of work relative to what it tells you, and the answer determines whether a site is a twelve-month project or a four-year one. If you're bidding on land in the Solent, Poole Harbour, the Wensum, the Tees or any of the other affected catchments, run the numbers before you commit. **Read the local plan evidence base, not just the policy map.** W1 means the infrastructure engagement behind an emerging plan is now formally part of how growth is located and phased. If your site is in a plan and the utility engagement says the network can't serve it until 2032, that will show up in the phasing — and it is much better to know that at option stage. **NutrientMonkey** implements Natural England's published nutrient-budget methodology across all 27 NE catchments in your browser — nitrogen, phosphorus or both, with the 20% buffer included. Building your assessment on screen is free; the planning-ready PDF is £79 +VAT (£94.80 inc VAT). It's a planning-support tool, not the statutory NE calculator, and the report says so. [Try NutrientMonkey →](/tools/nutrient-neutrality-calculator/) If you've got a site in a protected catchment and you're trying to work out what the mitigation actually costs, [get in touch](/contact/) and we'll run the budget with you. *Sources: [National Planning Policy Framework, August 2026 (PDF), GOV.UK](https://assets.publishing.service.gov.uk/media/6a8334c03bd75b81e2329ac4/National_Planning_Policy_Framework.pdf) — chapter 10, policies W1–W4 and footnote 33 · [National Planning Policy Framework guidance page, MHCLG, 17 August 2026](https://www.gov.uk/guidance/national-planning-policy-framework) · [New planning framework puts water infrastructure at heart of future development, Water Magazine, 18 August 2026](https://www.watermagazine.co.uk/2026/08/18/new-planning-framework-puts-water-infrastructure-at-heart-of-future-development/)* --- # Your soakaway design now has a named rulebook — NPPF policy F8 URL: https://energycount.co.uk/news/nppf-2026-suds-national-standards-policy-f8/ Date: 2026-08-21 Drainage has always been the quiet part of a planning submission. You do the infiltration tests, size the soakaway, write the strategy, and hope the Lead Local Flood Authority agrees with your assumptions. What has been missing is a single document everyone is measuring against. The **National Planning Policy Framework published on 17 August 2026** goes some way to fixing that. Flood risk and coastal change now has its own chapter — **nine coded policies, F1 to F9** — plus a dedicated **Annex F**, and the Framework is explicit that "the annexes included with this Framework are also national planning policy". The policy that changes day-to-day work is **F8**, on sustainable drainage. ## What F8 does Two things, both practical. **It names the standard.** Development proposals with drainage implications should incorporate sustainable drainage systems, and those systems should be **designed in accordance with the National Standards for Sustainable Drainage Systems**. That's Defra's guidance, published 19 June 2025 and updated 30 July 2025. Until now it sat in an awkward position — a serious technical document that nobody was formally required to follow. National planning policy now points at it by name. **It brings the Lead Local Flood Authority into the frame for major development.** Major schemes are expected to take account of LLFA advice, which formalises a conversation most competent applicants were having anyway — but gives the LLFA's position more weight when it isn't. There's also a watercourse limb: development should not enclose existing watercourses without compelling reasons, and de-culverting and re-naturalising river channels is encouraged where possible. The Framework's climate policy reinforces all of this. Policy **CC3** on adaptation asks development to: > "Incorporate sustainable drainage systems to manage surface water flow rates and reduce volumes of runoff in accordance with policy F8" So SuDS is now cross-referenced from the climate adaptation policy as well as sitting in the flood chapter. It is harder than it used to be to treat drainage as a detail to be resolved after layout. ## What the National Standards actually ask for If you haven't read them since they landed, this is the part worth knowing. The 2025 standards replaced the thin 2015 non-statutory technical standards with **seven standards** that go well beyond peak flow control: 1. **Runoff destinations** — a drainage hierarchy. Collect for non-potable use first, then **infiltrate to ground**, then discharge to a surface water body, then a surface water sewer, and only last a combined sewer. Evidence is expected to justify anything lower down the list. 2. **Management of everyday rainfall** — intercept the first **5 mm of rainfall** so it doesn't leave the site as runoff. 3. **Management of extreme rainfall and flooding** — design requirements for infiltration features and allowable discharge rates. 4. **Water quality** — a risk assessment tailored to the land use and pollution risk. 5. **Amenity** — multi-functional places and landscapes. 6. **Biodiversity** — including links to Biodiversity Net Gain and Local Nature Recovery Strategies. 7. **Design for construction, operation, maintenance, decommissioning and structural integrity** — long-term maintenance planned in, not assumed. Look at the first standard again. **Infiltration sits second in the hierarchy**, behind rainwater reuse and ahead of every piped option. On most sites that means the honest answer to "can we soak away?" needs to be established with real infiltration testing, and it needs to be established early enough to influence the layout — not after the plots are drawn and there is nowhere left to put a soakaway at the required distance from foundations. ## What hasn't changed Worth being clear about the limits. **Schedule 3 of the Flood and Water Management Act 2010 is still not commenced in England.** There is no SuDS Approving Body, no separate statutory approval, and no legal duty in the way there is in Wales. Ministers have said repeatedly that better delivery may come through planning policy, adoption and maintenance rather than commencement, and that a final decision will be made "in due course". **The National Standards themselves remain non-statutory guidance.** What F8 does is give them a route into every planning decision, because the NPPF is a material consideration of critical importance. That's a real change in weight, not a change in legal status. The practical effect is the same either way: if your drainage strategy departs from the standards, you now need a reason you're willing to write down. ## What we'd suggest doing Test early, and test properly. The single most common cause of a drainage strategy unravelling is an infiltration rate assumed at layout stage and disproved at technical approval. **BRE Digest 365** sets out the trial pit method — three fills, the rate taken between 75% and 25% of the effective depth — and it takes a day on site plus a return visit. Doing it before the layout is fixed is cheap. Doing it after is a redesign. The second is soakaway sizing checked at a single storm duration. The worst case isn't always the shortest, heaviest storm — a long, moderate storm can fill a slow-draining soakaway that a cloudburst wouldn't. BRE 365 asks you to check a range of durations, at the design return period with a climate change uplift, and take whichever needs the most storage. **SoakMonkey** runs the BRE Digest 365 soakaway method in your browser — infiltration rate from your percolation results, storage sizing tested across storm durations, and a Building Control-ready report. Sizing on screen is free; the PDF export is £25 +VAT (£30 inc VAT). [Try SoakMonkey →](/tools/soakaway-calculator/) If you've got a planning condition asking for a SuDS strategy to the National Standards and you're not sure your site will infiltrate, [get in touch](/contact/) — a trial pit and an hour of sizing usually settles it. *Sources: [National Planning Policy Framework, August 2026 (PDF), GOV.UK](https://assets.publishing.service.gov.uk/media/6a8334c03bd75b81e2329ac4/National_Planning_Policy_Framework.pdf) — chapter 18 (policies F1–F9), Annex F, policy CC3 · [National standards for sustainable drainage systems (SuDS), Defra, GOV.UK](https://www.gov.uk/government/publications/national-standards-for-sustainable-drainage-systems/national-standards-for-sustainable-drainage-systems-suds) · [Sustainable Drainage Systems (SuDS), House of Commons Library briefing CBP 10483, 4 February 2026](https://commonslibrary.parliament.uk/research-briefings/cbp-10483/) · [New planning framework puts water infrastructure at heart of future development, Water Magazine, 18 August 2026](https://www.watermagazine.co.uk/2026/08/18/new-planning-framework-puts-water-infrastructure-at-heart-of-future-development/)* --- # Part F 2026 puts ventilation ductwork in front of Building Control URL: https://energycount.co.uk/news/part-f-2026-ductwork-evidence-building-control/ Date: 2026-08-20 Ventilation ductwork has never been the glamorous end of Building Regulations. It gets designed late, squeezed into whatever space is left, and finished with a metre of concertina'd flexible duct behind a hatch. **Approved Document F Volume 1, 2026 edition** takes a much firmer line — and unusually, it asks for paperwork before the ceiling goes on. It's a short change, but it alters how jobs get run. ## Rigid is now the default The 2026 guidance is specific about what ducts should be made of: - **Centralised continuous MEV and MVHR** systems should use **rigid or smooth semi-rigid ducts**. - **Intermittent extract fans and decentralised (d-MEV) fans** should use **rigid ducting**, with a maximum duct length of **2.0 m where practical**. - **Flexible ductwork is limited to 200 mm in length**, and only for final connections to fan unit spigots on centralised MEV or MVHR systems. - Where a system's fan control relies on constant pressure within the ductwork, **flexible ducting is not permitted anywhere in the system**. Any flexible duct that is used has to be installed so the full internal diameter is maintained and flow resistance is minimised — no sagging, no crushing, no lazy bends. ## A hard ceiling on static pressure AD F 2026 introduces **Table 1.8**, which caps the *designed* system static pressure for centralised continuous MEV and MVHR by total flow rate: | Total air flow rate | c-MEV (multiple extract spigots) | MVHR / MEV (single extract spigot) | | --- | --- | --- | | Up to and including 37 l/s | 30 Pa | 60 Pa | | 38 to 53 l/s | 50 Pa | 110 Pa | | 54 l/s and above | 80 Pa | 160 Pa | Paragraph 1.81 sets out how you're expected to hit those numbers: minimise overall duct length, minimise bends and offsets, and size the ducts appropriately for the flow rate. None of that is new engineering advice — it's just now written down as guidance you can be held to. ## The evidence requirement This is the one to flag with site teams. **Paragraph 1.78**: for all systems with a duct length greater than **2.0 m**, design calculations and drawings should be provided **to the building control body** to demonstrate that the fans, the connected ducting and the external air terminal can achieve the required flow rates, and that the static pressure principles have been met. That evidence should come from **a suitably competent person**. Two metres is not a lot of duct. In practice, most centralised MEV and MVHR installations — and plenty of d-MEV runs — will clear that threshold, which means a ventilation design package becomes a routine Building Control submission rather than something worked out on site. ## The insulation rule that reads backwards Paragraph 1.83 asks for **more** duct insulation in heated space than in cold. Intake and exhaust ductwork through conditioned areas — the heated part of the dwelling — needs the equivalent of at least **50 mm** of material at ≤0.04 W/(m·K), fully vapour sealed. Through unheated areas such as lofts and sub-floor voids, it drops to **25 mm**. Read as a Part L heat-loss rule that looks like a typo. It isn't one: it's condensation control. Intake and exhaust ducts are the two runs between the unit and the outside world, so they carry air at roughly outdoor temperature. Push a duct full of 2°C air through a warm, humid hallway and its surface sits below the room's dew point — you get condensation on the *outside* of the duct, and it finds its way through the ceiling. In a cold loft, duct and surroundings are at much the same temperature, so there's little driving force. The exhaust run is arguably the greater risk of the two: after heat recovery that air has been cooled and is close to saturation. **Mind the terminology.** In Part F, "intake" means the outdoor air intake — Section 2 is all about siting intakes away from traffic and downwind of exhaust outlets. It does *not* mean the supply ducts delivering tempered air to habitable rooms. An MVHR unit has four runs: intake and exhaust (unit to outside, covered by 1.83), and supply and extract (unit to rooms, not covered). Supply air leaves the heat exchanger close to room temperature, so it isn't a condensation risk indoors. That leaves a gap worth closing yourself. An MVHR supply or extract duct crossing a cold loft carries near-room-temperature air through an unheated space — a genuine heat-loss and condensation risk that paragraph 1.83, read strictly, doesn't cover. The installation checklist at paragraph 4.19(g) is looser, asking that "all ductwork is insulated following the guidance in paragraph 1.83", so expect some Building Control bodies to read it as covering everything. Insulating supply and extract runs in unheated spaces is sensible practice regardless of which reading you take. ## The rest of the detail A few more things worth having on the checklist: - **External air terminals** should have a free area of at least **90%** of the free area of the duct they serve. A restrictive grille can undo an otherwise good design. - **Connections** should be both mechanically secured and adequately sealed; flexible ducts need mechanical fastenings such as rigid connectors or jubilee clips. - **Access for maintenance** must be reasonable, and on MVHR units filter access should not require tools or removal of the main front cover. ## Why it matters Industry evidence has said the same thing for years: the gap between designed and delivered ventilation performance is usually an *installation* gap, not a design one. A well-specified MVHR system with 3 m of crushed flexible duct on the kitchen extract will underperform quietly, and nobody finds out unless it's measured. AD F 2026 attacks that from both ends — tighter rules on what gets installed, and a requirement to show your working to Building Control before it's buried. The amended Approved Documents L and F come into force on **24 March 2027** for most new building work (**24 September 2027** for higher-risk building work), with transitional protection to 24 March 2028 for qualifying plots. Systems being designed now for 2027 starts should already be working to these rules. ## Worth doing now Pull the ventilation design forward in the programme. Decide unit locations and duct routes early enough that they can be short and straight, allow space for insulation, and make sure someone owns the design calculations that Building Control will ask for. It's a lot cheaper than re-routing ductwork through a plasterboarded ceiling. If you're working through an FHS-compliant plot and want a second pair of eyes on how the Part L and Part F requirements stack up together, [get in touch](/contact/). *Sources: [Approved Document F Volume 1, 2026 edition (PDF), GOV.UK](https://assets.publishing.service.gov.uk/media/69c12224d588c92c483e4b6a/ADF1_2026.pdf) — paragraphs 1.75 to 1.86 and Table 1.8 · [CIBSE Journal CPD Module 266: Ventilation design under the Future Homes Standard, July 2026](https://www.cibsejournal.com/cpd/modules/2026-07-env/) · [The Building Regulations etc. (Amendment) (England) Regulations 2026 (SI 2026/335), legislation.gov.uk](https://www.legislation.gov.uk/uksi/2026/335/made)* --- # Part F 2026 has a definition that could catch you out — 'highly airtight' URL: https://energycount.co.uk/news/part-f-2026-highly-airtight-dwellings/ Date: 2026-08-20 Most of the Future Homes Standard conversation has been about Part L — the notional dwelling, heat pumps, PV, U-values. But the change that's most likely to bite on site sits in the other document. **Approved Document F Volume 1, 2026 edition** introduces a formal split between "less airtight" and "highly airtight" dwellings, and that single definition decides what ventilation system you're allowed to use. ## The definition AD F 2026 defines it in the glossary. A **highly airtight dwelling** is one that achieves one or both of the following: - a **design air permeability lower than 5 m³/(h·m²) at 50 Pa**, or - an **as-built air permeability lower than 3 m³/(h·m²) at 50 Pa**. Everything else is a "less airtight dwelling". That's the whole test — two numbers. Now put it next to Part L. The FHS notional dwelling under the SAP 10.3 route assumes an air permeability of **4 m³/(h·m²)**, against a legal backstop that stays at 8. So a dwelling designed to match the notional specification is, by definition, a highly airtight dwelling under Part F. The two documents are deliberately joined at the hip. ## Why the label matters Table 1.6 of AD F 2026 sets out which ventilation systems the guidance covers for which dwellings: - **Natural ventilation** — background ventilators plus intermittent extract fans — is listed as suitable for **less airtight dwellings only**. - **Continuous mechanical extract ventilation** (centralised c-MEV or decentralised d-MEV) covers **all dwellings**. - **Mechanical ventilation with heat recovery** covers **all dwellings**. In other words, once a home is highly airtight, trickle vents and a humidistat fan in the bathroom stop being a route to compliance. You need continuous mechanical ventilation, or a specialist design. That's not surprising in itself — squeeze out uncontrolled infiltration and something has to replace it. What's new is that the guidance now says so explicitly, with a number attached. ## The bit that catches people out Here's the paragraph worth reading twice. **AD F 2026, paragraph 1.46**: where a dwelling has natural ventilation and a *measured* air permeability that differs from the *design* air permeability, so that it becomes defined as a highly airtight dwelling, one of the following applies: - expert advice should be sought, or - a continuous mechanical extract ventilation system should be installed. Read that as a site scenario. A plot is designed at, say, 5.5 m³/(h·m²) with a natural ventilation strategy — perfectly reasonable, less airtight dwelling, trickle vents and intermittent extract. The build team does a genuinely good job on the tapes and seals. The as-built test comes back at 2.8. That plot is now a highly airtight dwelling, and the ventilation system that's already installed is no longer the one the guidance supports. Building tighter than you designed used to be a small bonus on the SAP result. Under AD F 2026 it can also be a compliance problem — and it lands right at the end of the programme, after first fix. The practical answer is to decide early. If there's any prospect of the as-built result coming in under 3, design for continuous mechanical ventilation from the start rather than hoping the test lands in the right band. ## What continuous MEV actually asks for If you do land in continuous extract territory, a few of the numbers are worth having to hand: - **Whole-dwelling ventilation rate** — the higher of 0.3 l/s per m² of internal floor area (all floors) and the bedroom-based figure in Table 1.3: 19 l/s for one bedroom, 25 for two, 31 for three, 37 for four, 43 for five, adding 6 l/s per bedroom beyond that. If the dwelling has only one habitable room, 13 l/s. - **Total continuous extract** should be at least the whole-dwelling ventilation rate. - **Background ventilators are still required** with c-MEV and d-MEV. They should not be in wet rooms, should provide a minimum equivalent area of 4,000 mm² per habitable room, and the total number should equal **the number of bedrooms plus two** — so a one-bed needs three, a two-bed needs four. They're meant to be left open. - **Internal doors** need a free area equivalent to a 10 mm undercut in a 760 mm door, measured above the finished floor. MVHR is the exception on background ventilators: because the unit supplies filtered air to habitable rooms directly, they aren't required — but you then need room for two sets of ductwork, and AD L 2026 wants at least 73% heat recovery efficiency plus a summer bypass. ## When this applies The amended Approved Documents L and F come into force on **24 March 2027** for most new building work, and **24 September 2027** for higher-risk building work, with transitional protection running to 24 March 2028 for plots that qualify. If you're designing now for a 2027 start, you're designing to these rules. ## What to do about it Three things worth doing before the deadline gets close: 1. **Pick the ventilation strategy from the target air permeability, not the other way round.** If the design figure is under 5, natural ventilation is off the table from day one. 2. **Stress-test the "we built it too well" scenario.** Ask what happens if the as-built test comes back under 3, and make sure the answer isn't "retrofit a ducted system into a finished house". 3. **Get the junctions right anyway.** Airtightness and thermal bridging live in the same places — junctions, penetrations, service voids. Tighter fabric makes both your psi-values and your air test result more important, and neither is something you want to discover late. **ΨMonkey** calculates bespoke PSI values for your junctions to BR 497 and BRE IP 1/06 conventions, so the details you're actually building show up in your SAP model instead of the worst case the software assumes. [Try ΨMonkey →](/tools/psi-calculator/) And if you've got a plot where the air test has come in tighter than the design figure and you're not sure where that leaves the ventilation strategy, [get in touch](/contact/) — it's a conversation worth having before first fix, not after. *Sources: [Approved Document F Volume 1, 2026 edition (PDF), GOV.UK](https://assets.publishing.service.gov.uk/media/69c12224d588c92c483e4b6a/ADF1_2026.pdf) — glossary definition of "highly airtight dwellings", Tables 1.3 and 1.6, and paragraphs 1.20, 1.21, 1.46 and 1.64 · [CIBSE Journal CPD Module 266: Ventilation design under the Future Homes Standard, July 2026](https://www.cibsejournal.com/cpd/modules/2026-07-env/) · [The Building Regulations etc. (Amendment) (England) Regulations 2026 (SI 2026/335), legislation.gov.uk](https://www.legislation.gov.uk/uksi/2026/335/made)* --- # Councils can still beat Part L — but only as a percentage uplift on TER URL: https://energycount.co.uk/news/nppf-2026-local-energy-standards-ter-uplift/ Date: 2026-08-19 If you've ever run a SAP calculation twice — once for Building Control and once for a local plan policy demanding "a 35% improvement on Part L" — you'll have followed the NPPF consultation with some interest. The **December 2025 draft NPPF** proposed, at policy **PM13**, that local plans should not set quantitative standards covering matters already addressed by Building Regulations. Read literally, that would have ended local energy, carbon and overheating targets: Building Regulations would have become both the floor and the ceiling. The consultation closed on 10 March 2026 and drew a lot of noise from councils and the low-energy sector. The **final Framework was published on 17 August 2026**, replacing the December 2024 version. On this point, the government changed its mind. ## What PM13 actually says now Policy PM13 still tells plan-makers that quantitative standards should "not cover matters that are already addressed by Building Regulations" — but it now carves out three exceptions. The energy one is worth reading properly: > "Energy efficiency, for which any standards that go beyond the current or proposed Building Regulations should have a clear and robustly costed rationale which shows that there will not be an adverse impact on the viability and deliverability of development. Any such standards should be expressed as a percentage uplift of a dwelling's Target Emissions Rate (TER) calculated using a specified version of the Standard Assessment Procedure (SAP) or other approved calculation methodology." The other two exceptions are **accessibility** (M4(2)/M4(3), set in accordance with policy HO5) and **water efficiency** (the tighter optional requirement where justified, or exceptionally something more stringent in areas of serious water stress). So local ambition survives. But it has to arrive in a specific currency. ## Why the "percentage uplift on TER" wording matters This is the part that lands on assessors' desks rather than planners'. At the moment, local energy policies are written in whatever unit the authority fancied at the time: kgCO₂/m²/yr targets, space-heating demand limits in kWh/m²/yr, "net zero carbon" definitions, energy use intensity caps, Passivhaus-equivalent wording. Some of those can't be evidenced from a SAP output at all, which is how you end up with a planning condition that no compliance calculation can cleanly discharge. PM13 pushes all of that back into a single, familiar metric — **DER against TER, as a percentage** — and requires the plan to name **which version of SAP** the percentage is measured against. That last clause is not a footnote. A "31% uplift" means something quite different under SAP 10.2 than it does against the **SAP 10.3** notional building used for the Future Homes Standard, where the target has already moved a long way. A policy that doesn't pin its version down is a policy that will be argued about at appeal. There's also a viability test attached: the rationale must be "clear and robustly costed" and show no adverse impact on the viability and deliverability of development. Expect that to be where most of the examination argument happens. ## The Future Homes Standard collision Worth holding both dates in your head. The **Future Homes and Buildings Standards** come into force on **24 March 2027** for non-higher-risk work, with transitional protection for plots where a valid application was made before that date and work is commenced before **24 March 2028**. From then, the notional dwelling gets very demanding indeed — and requirement L3 mandates on-site renewable electricity generation. A local policy demanding a percentage uplift on a *post-FHS* TER is a materially different ask from the same percentage against the 2021 baseline. Many existing local plan policies were written against Part L 2013 or 2021 targets and will need revisiting; PM13 gives examiners a clear basis for asking authorities to show their working. ## What this means in practice **If you're a housebuilder or developer:** check the energy policies in the local plans covering your live sites, and specifically whether they name a SAP version. Where they don't, the new PM13 wording is a reasonable basis for asking the authority what baseline it thinks it is measuring against — before you price the specification. **If you're an assessor:** expect more requests for a *dual* output — the Part L compliance case, plus a stated percentage improvement of DER over TER for the planning condition. Getting both from a single, consistent model saves an argument later. **If you're in Building Control:** nothing changes for you directly. PM13 is a plan-making policy. But it should, over time, reduce the number of planning conditions that ask for something Building Control has no way of verifying. ## What we'd suggest doing now Don't rewrite specifications on the strength of a planning policy that may itself be revised. Do find out where you actually sit. For a percentage-uplift policy, the number that decides everything is the **DER/TER margin** — and on most schemes the cheapest place to find margin is the thermal bridging. Default PSI values are deliberately pessimistic; calculated junction values routinely recover several percent of the emissions rate without changing a single product on the specification. **ΨMonkey** calculates bespoke PSI values for your junctions to BR 497 and BRE IP 1/06 conventions, so your SAP model reflects the details you're actually building rather than the worst case the software assumes. [Try ΨMonkey →](/tools/psi-calculator/) If you've got a site where a local plan energy policy and the Part L case are pulling in different directions — or a condition that names no SAP version at all — [get in touch](/contact/) and we'll tell you how we'd approach it. *Sources: [National Planning Policy Framework, August 2026 (PDF), GOV.UK](https://assets.publishing.service.gov.uk/media/6a8334c03bd75b81e2329ac4/National_Planning_Policy_Framework.pdf) · [Full steam ahead to fast-track more homes near stations — MHCLG press release, 17 August 2026](https://www.gov.uk/government/news/full-steam-ahead-to-fast-track-more-homes-near-stations) · [The Building Regulations etc. (Amendment) (England) Regulations 2026 (SI 2026/335), legislation.gov.uk](https://www.legislation.gov.uk/uksi/2026/335/made)* --- # The new NPPF keeps local water efficiency standards on the table URL: https://energycount.co.uk/news/nppf-2026-local-water-efficiency-standards/ Date: 2026-08-19 There's a running theme in water efficiency policy: everyone agrees the standard should be tighter, and nobody agrees on who should set it. Earlier this month we covered **Water UK backing Defra's proposed cut from 125 to 105 l/p/d**, and its argument for a **single national standard** rather than a patchwork of locally set numbers. The **National Planning Policy Framework published on 17 August 2026** has now answered the second half of that question, and the answer is: not yet. ## What the Framework says Policy **PM13** tells plan-makers that quantitative standards in local plans should not cover matters already addressed by Building Regulations. Water efficiency is one of only three carve-outs: > "Water efficiency, for which it may be appropriate to apply the tighter Building Regulations optional requirement where justified, or exceptionally a more stringent local standard in areas of serious water stress" The plan-making climate policy reinforces it. Policy **CC1** requires development plans to take a proactive approach to climate mitigation and adaptation, including by "setting local water efficiency standards for new development where these are justified in accordance with policy PM13". Two things follow from that wording. **First, the 110 route is explicitly endorsed.** The Part G optional requirement of **110 l/p/d** remains available to authorities that can justify it — which, in practice, is most of the south and east of England. **Second, and more interesting: "exceptionally, a more stringent local standard".** That is national policy sanctioning numbers *below* 110 in areas of serious water stress. It doesn't say what those numbers should be, or how they'd be calculated, which leaves the door open for the 100 and 95 l/p/d policies that a handful of authorities have already pushed for. The check on all of this is the same one applied to energy standards: the rationale must be justified and proportionate, and PM13 as a whole requires evidence that standards won't undermine viability and deliverability. ## Why this matters now The timing is awkward in a useful way. Defra consulted on cutting the mandatory Part G standard from **125 to 105 l/p/d**, with a fittings-based compliance route, and the government response is still pending. If that lands, the national baseline moves below today's optional requirement — and the whole optional-requirement architecture will need rethinking, because a 110 l/p/d "tighter" standard makes no sense once the mandatory floor is 105. The NPPF doesn't pre-empt that. It just keeps the local mechanism in place in the meantime. So for the next stretch, you're likely to be working with: - A **mandatory** standard of 125 l/p/d, heading for 105 - An **optional** standard of 110 l/p/d applied by many local plans - A small number of authorities pressing for **below 110** on serious water stress grounds - No national consolidation of any of it If you build across more than one authority, that's three different numbers to track per site, plus the possibility of a fourth. ## What it means for your calculations The practical consequences are unchanged in kind, but sharper in degree. The levers are the same as ever — **shower flow rate, bath capacity, WC flush volumes, basin and kitchen tap flow rates**, with rainwater and greywater reuse as the heavier tools. What changes is headroom. A specification that clears 110 comfortably may have very little left if a local policy lands at 100, and a bath plus a generous shower head will use most of that margin between them. There's also an evidence point worth noting for anyone responding to a local plan consultation. PM13 requires standards to be justified with proportionate evidence, and the "exceptionally" in the water clause is doing real work — it signals that sub-110 standards are meant to be rare and well-evidenced, not a default ambition. If a draft policy in your area proposes one without that evidence, the Framework now gives you clear language to point at. ## What we'd suggest doing Know your number per authority, not per company. Run each standard house type through the official methodology at the standards that actually apply to your sites — 125, 110, and whatever the local plan is proposing — and find out which types have margin and which are living on the edge. One dwelling type covers every identical plot, so this is a small piece of work that maps your whole exposure. **WaterMonkey** runs the full official Part G water efficiency methodology with live PASS/FAIL as you type at 125 or 110 l/p/d, rainwater and greywater included, free in your browser. Building Control-ready PDF reports are £25 +VAT, and one dwelling type covers every identical plot on the site. We'll add the new standard as soon as Defra confirms it. [Try WaterMonkey →](/tools/part-g-water-calculator/) If you've got a planning condition asking for something tighter than 110 l/p/d and you're not sure it's achievable with the specification you've priced, [get in touch](/contact/) and we'll tell you where the margin is. *Sources: [National Planning Policy Framework, August 2026 (PDF), GOV.UK](https://assets.publishing.service.gov.uk/media/6a8334c03bd75b81e2329ac4/National_Planning_Policy_Framework.pdf) · [Full steam ahead to fast-track more homes near stations — MHCLG press release, 17 August 2026](https://www.gov.uk/government/news/full-steam-ahead-to-fast-track-more-homes-near-stations) · [Review of Water Efficiency Standards in the Building Regulations 2010 — Defra consultation](https://consult.defra.gov.uk/water-efficiency-demand/review-of-water-efficiency-standards)* --- # The Future Homes Standard transitional trap — 'commenced' doesn't mean what you think URL: https://energycount.co.uk/news/future-homes-standard-transitional-deadline-commencement/ Date: 2026-08-18 Most housebuilders we speak to have the first date in their heads: **24 March 2027**. That's when the Future Homes and Buildings Standards bite, and the received wisdom is "get the application in before then and you're fine". It's the second date that catches people out — and the definition sitting behind it. Getting that right now beats a nasty surprise in 2028. ## The two-part test The Future Homes Standard is delivered by **The Building Regulations etc. (Amendment) (England) Regulations 2026** (SI 2026/335), made on 23 March 2026 and laid before Parliament the following day. The Regulations come into force on **24 March 2027**, except that regulations 3, 4, 6, 7, 8 and 9 come into force for **higher-risk building (HRB) work and work to an existing HRB on 24 September 2027**. For ordinary, non-HRB work, **regulation 5** sets out the transitional protection. It applies to building work on a particular building where: 1. a **building notice, an initial notice, or an application for building control approval with full plans** has been given to the relevant authority in respect of that building **before 24 March 2027**; **and** 2. the building work to which that notice or application relates is **commenced in relation to that building before 24 March 2028**. Both limbs have to be satisfied. Miss either one and the amendments made by regulations 3 and 4 — the new Part L, requirement L3 and the rest — apply to the work. Two things are easy to miss here. The first is that this is expressed **per building**, not per site. An early full-plans application does not throw a blanket over a whole scheme; each individual building has to have commenced in time. The second is that "commenced" has a legal meaning, and it isn't a generous one. ## What "commenced" actually means Regulation 5(5) is explicit: paragraphs (2) to (5) of **regulation 46A** of the Building Regulations 2010 apply to determine whether work is regarded as commenced. Regulation 46A was written for a different purpose — the lapse of building control approval — but it's now doing double duty as the FHS cut-off test. For **the construction of a building** (and for a horizontal extension), regulation 46A(3) says work is regarded as commenced when: > the sub-surface structure of the building or the extension including all foundations, any basement level (if any) and the structure of ground floor level is completed. Read that again. Not "started on site". Not "foundations poured". The sub-structure has to be **complete, including the ground floor structure**, on that specific building, before 24 March 2028. There are two variants: - **Complex buildings** (regulation 46A(2)) — commencement is when the foundations supporting that building and the structure of its lowest floor level are completed. A "complex building" means one sharing a foundation plinth or podium with another building or structure, one with more than one storey below ground, or one intended primarily as a public building with capacity for 100 or more visitors. - **Any other building work** (regulation 46A(4)) — commencement is when the work identified in the client's statement as amounting to **15% of the proposed work** is completed. Site clearance, service diversions, roads and sewers, hoarding — none of that gets a plot over the line. ## Higher-risk buildings work differently For HRB work, work to an existing HRB, and stages of HRB work, regulations 6 to 8 use a different mechanism: protection depends on a **valid building control approval application having been submitted to the regulator before 24 September 2027** and not being rejected before or after that date. There's no separate commencement deadline — but a rejection kills the protection, which given Gateway 2 rejection rates is not a theoretical risk. Helpfully, where protection is triggered by an application for a *stage* of HRB work, it carries through to subsequent stages provided the original application hasn't been rejected or lapsed. ## And the older transitional arrangements are going Regulation 10 revokes the transitional arrangements in the 2013 Regulations and removes part of the 2021 equivalent, subject to savings. If you have plots that have been sitting under a 2013 saving, they need to be started before 24 March 2028 too, or they fall into the new regime. ## What you're falling into if you miss it It's worth being clear about the size of the gap. From 24 March 2027 the amended Part L is retitled **"Energy and greenhouse gas emissions"**, requirement L1 is rewritten around minimising greenhouse gas emissions as well as conserving fuel and power, and a brand-new functional requirement **L3** applies: when a building is erected which is or contains one or more dwellings, a **system for on-site renewable electricity generation** must be installed on the building or within its curtilage, designed so residents can use the electricity and capable of a reasonable output given the building's design and surroundings. There are limited exemptions — buildings exempt under regulation 7(4), buildings where a reasonable output genuinely isn't possible, and cases where an equivalent off-building on-site system already serves the residents. The definition of "fixed building services" also widens to include lifts, escalators and moving footways in new buildings (excluding those within individual dwellings), and a new regulation 40C requires that information owed to new-dwelling owners under regulations 39 to 40B is actually provided **in an appropriate format**. Alongside all this sit the new **Approved Document L Volumes 1 and 2 (2026)** and **Approved Document F Volume 1 (2026)**. That's not a tweak. A plot that slips from the old regime to the new one is a redesign, not a re-run of the calculation. ## The practical move Two things are worth doing now: 1. **Map your plots against both dates**, building by building — application in before 24 March 2027, sub-structure complete before 24 March 2028. Any plot where the programme has the ground floor slab landing in early 2028 is a plot at risk. 2. **Model the FHS case for the plots you know won't make it**, rather than discovering the shortfall late. Fabric, thermal bridging and the L3 renewables requirement all move together, and the cheapest time to find the answer is before the house types are frozen. If you'd like the Part L and SAP 10.3 modelling done properly — including bespoke PSI values for your junctions rather than defaults that quietly wreck the DER — [get in touch](/contact/) and we'll tell you how we'd approach your scheme. *Sources: [The Building Regulations etc. (Amendment) (England) Regulations 2026 (SI 2026/335), legislation.gov.uk](https://www.legislation.gov.uk/uksi/2026/335/made) · [Regulation 46A, The Building Regulations 2010, legislation.gov.uk](https://www.legislation.gov.uk/uksi/2010/2214/regulation/46A) · [The Future Homes and Buildings Standards: Building Circular 01/2026, GOV.UK](https://www.gov.uk/government/publications/the-future-homes-and-buildings-standards-building-circular-012026/the-future-homes-and-buildings-standards-building-circular-012026-letter)* --- # New-build EPCs held up while the rest of the market fell — the Q2 2026 numbers URL: https://energycount.co.uk/news/new-dwelling-epc-statistics-q2-2026/ Date: 2026-08-18 Quarterly statistics rarely make anyone's day, but this set is worth a look — partly for what it says about new-build volumes heading into the Future Homes Standard, and partly because MHCLG has changed how it counts. The **Energy Performance of Buildings Certificates statistical release for April to June 2026** was published on 30 July 2026, followed on **12 August** by the companion release, *Energy efficiency characteristics of new dwellings*, which is MHCLG's Part L monitoring series. Here's the plain-English version of the headline data. ## New build held up; the rest of the market didn't In England in Q2 2026, **440,000 domestic EPCs** were lodged on the Register — an 11% fall on the same quarter in 2025. But that fall is almost entirely on the existing-stock side: - **New dwellings: 51,000 EPCs, up 2%** on Q2 2025 - **Existing dwellings: 389,000 EPCs, down 12%** Over the **12 months to June 2026**, England recorded **203,000 new-dwelling EPCs, a 3% increase** on the previous year. Across England and Wales combined, new-dwelling lodgements rose 2% to 53,000 in the quarter while existing-dwelling lodgements fell 12% to 411,000. Because EPCs for new dwellings are lodged as a matter of course on completion, they're a reasonably good early read on housing supply — MHCLG uses them, adjusted for demolitions, as an indicator of progress towards the 1.5 million homes target. The divergence between the two lines is essentially the sales-and-lettings market cooling while completions hold steady. Regionally, the biggest year-on-year rise in new-dwelling lodgements was in the **West Midlands (up 24%)**; the biggest fall was in the **South East (down 11%)**. In Wales, 2,000 new-dwelling EPCs were lodged, up 5%, against 22,000 for existing dwellings, down 6%. ## Ratings: 89% A or B, and stuck there **89% of new dwellings in England were rated A or B** — unchanged from the same quarter in 2025. Wales came in at the same 89%, with 10% at C or D. That flatness is the interesting part. Under the 2021 Part L uplift, band B has become the default outcome rather than a stretch, and the ratings distribution has essentially stopped moving. The 2026 Approved Document L, with the new requirement L3 for on-site renewable electricity generation, is what shifts it again — and those homes won't start appearing in these statistics in volume until 2027–28. ## The methodology change worth noting Buried in the "changes to this release" section: MHCLG has carried out **additional de-duplication of new-dwelling EPCs that lack a UPRN**. New dwellings often have more than one EPC on the Register — one lodged against the design and another after a change during construction — and the extra cleaning strips more of those duplicates out. The practical effects: - New-dwelling figures are **slightly lower (less than 1%) across all quarters**, historically as well as currently. - The **live tables have been revised** back through the series; **previously published statistical releases have not** been changed. - **Existing dwellings, non-domestic EPCs and DECs are unaffected.** If you quote new-dwelling EPC counts in bids, land appraisals or board packs, make sure you're pulling from the revised live tables rather than an older release, or your year-on-year comparison will be built on two different methodologies. ## What to take from it For assessors, the message is that new-build SAP work is holding up while RdSAP volumes on the existing stock are visibly softening — a useful thing to know if you're deciding where to put your training and accreditation budget over the next year. For housebuilders, a flat 89% A-or-B tells you the current regime has been fully absorbed and the next step change is a regulatory one, not a market one. The next quarterly release, covering July to September 2026, is expected on **29 October 2026**. If you'd like your new-build Part L and SAP 10.3 work handled properly — including bespoke thermal-bridging PSI values instead of punitive defaults — [get in touch](/contact/) and we'll tell you how we'd approach your scheme. *Sources: [Energy Performance of Buildings Certificates Statistical Release: April to June 2026, England and Wales, GOV.UK](https://www.gov.uk/government/statistics/energy-performance-of-building-certificates-in-england-and-wales-april-to-june-2026/energy-performance-of-buildings-certificates-statistical-release-april-to-june-2026-england-and-wales) · [Energy efficiency characteristics of new dwellings: April to June 2026 (release announcement), GOV.UK](https://www.gov.uk/government/statistics/announcements/energy-efficiency-characteristics-of-new-dwellings-april-to-june-2026)* --- # RdSAP Conventions v12.2 are live — what changed on 6 August URL: https://energycount.co.uk/news/rdsap-conventions-v12-2-6-august-2026/ Date: 2026-08-16 If you produce EPCs on existing homes, the ground shifted slightly under you this month. The **RdSAP 10 Conventions v12.2** — the MHCLG-approved rulebook that tells domestic energy assessors how to interpret what they find on site — came into effect on **6 August 2026**, superseding v12.1 (which had run since August 2025). It's not a new methodology, but the detail matters: the revision history lists **16 amended conventions, four brand-new ones, and the deletion of Appendix 4**. Most of the changes are about squeezing out inconsistency between assessors, replacing "use your judgement" with a rule. Here are the ones worth reading twice. ## Bungalows and self-contained annexes The definition of a **bungalow** has been tightened: a property should only be recorded as a bungalow where **all habitable accommodation is at ground-floor level**. Chalet bungalows and anything with a room in the roof are now treated as houses. There's also clearer guidance on when an annexe counts as a **self-contained dwelling** needing its own EPC. It must have fixed cooking and bathing facilities — the cooking provision expected to include a fixed oven, a sink and either two fixed hot rings (for a one-bedroom dwelling) or four (for anything larger) — plus its own access, either from outside or via a communal corridor. An internal connecting door to the main house does not, on its own, stop the unit being self-contained. ## Rooms in roof: Convention 2.06 rewritten This is one of the biggest single changes, aimed at loft conversions and rooms in the roof: - **A new 25% rule for connected gable walls.** Where only part of a gable wall is connected to another part of the dwelling, it's treated as *exposed* if less than 25% is connected, and *connected* if more than 25% is. - **A new 20% dormer rule.** Small dormers taking up less than 20% of the room-in-roof floor area can be ignored when measuring the roof. Larger dormers must be measured separately — vertical faces as stud walls, roofs as flat ceilings. - **Hidden insulation.** Where there's clear evidence that insulation runs from the rafters through to the eaves, an unobservable stud wall can now be assumed to share the same insulation level, rather than defaulting to uninsulated. - **Complex geometry can be merged**, and in certain constructions you can now take U-values straight from **Table 18 of the RdSAP 10 Specification** rather than calculating each element. That last point is tied to the removal of **Appendix 4**, which previously covered room-in-roof U-values — those values are now inferred from Table 18 where the stated conditions are met. ## Conservatories with solid roofs Convention 2.28 now spells out the definition: for RdSAP purposes a conservatory is a building part where **50% or more of the external heat-loss walls are glazed and 75% or more of the roof is glazed**. Crucially, where a conservatory's roof has been replaced with a solid roof (or a false ceiling added) so it no longer meets that test, it must be **recorded as an extension**, with clear rules for how to enter the roof depending on pitch and the evidence available. This finally standardises one of the most argued-over judgement calls in the job. ## Heating, hot water and ventilation Several amendments pin down how systems are recorded: - **Heat-as-a-Service** gets its own new convention: where a provider owns or operates the heat generator, it's treated as **community heating** regardless of where the generator sits — entered as a community heat pump (electric) or community boiler (otherwise), with documentary evidence required. - **Electric combi boilers** (Convention 4.22) are now entered manually as a standard boiler, direct acting, fuel type electricity. - **Incomplete or condemned systems** (Convention 4.03) now explicitly covers **hot water** as well as heating — a fixed but non-working hot water source still counts when deciding the primary heating and hot water type. - **Two mechanical ventilation systems** get a new Convention 7.03e setting a clear order of precedence (MVHR first, then MV, MEV, PIV from outside, PIV from loft) where the software will only take one entry. ## Chimneys, evidence and PV batteries A few smaller but practical clarifications round it out. **Decommissioned chimneys with air bricks** (Convention 9.01) must now be considered: a ventilation opening under **30,000 mm²** is treated as a blocked chimney (20 m³/hr), larger openings as open (80 m³/hr). On **documentary evidence** (9.02), where you can see insulation and have evidence of intent but can't measure the thickness, you now record "insulated — insulation thickness unknown" rather than overstating or ignoring it. **PV batteries** over 5 kW (9.05) are split into a 5 kW entry plus a second battery for the excess. And an **air-tightness certificate** becomes invalid for RdSAP entry if material changes have been made to the property since the test (10.01). ## What to do about it None of this rewrites the RdSAP engine, but plenty of it changes the inputs — and inconsistent inputs are exactly what drives variation between assessors on the same house. The practical move is to read the full v12.2 document rather than rely on a summary, pay particular attention to the room-in-roof and conservatory rules if you survey a lot of older stock, and check that your software and accreditation scheme guidance reflect the new edition before you lodge. If you'd like the modelled, new-build side of the picture handled properly — SAP 10.3, Part L compliance and PSI-value thermal-bridging work — that's our patch. [Get in touch](/contact/) and we'll tell you how we'd approach your scheme. *Sources: [RdSAP Conventions v12.2 (MHCLG-approved), BRE Group](https://bregroup.com/documents/d/bre-group/rdsap-conventions-v12-2-mhclg-approved) · [Conventions (v12.1) for RdSAP 10, BRE Group](https://bregroup.com/documents/d/bre-group/rdsap-conventions-v12-1-21-august-2025-final) · [RdSAP Conventions v12.2: Key Changes for Energy Assessors, Energy Trust](https://energy-trust.co.uk/rdsap-conventions-v12-2-key-changes/)* --- # Domestic solar permitted development is being rewritten — what changes on 27 August 2026 URL: https://energycount.co.uk/news/gpdo-solar-permitted-development-27-august-2026/ Date: 2026-08-13 Solar rarely makes the news in our world, but a change landing this month is worth a look — especially if you specify PV on new homes or advise clients on what they can install without a planning application. On **27 August 2026**, a new order rewrites the permitted development (PD) rights for domestic solar in England, and for the first time writes **plug-in "balcony" solar** into the rules. ## What's actually changed The change comes via **The Town and Country Planning (General Permitted Development) (England) (Amendment) Order 2026** (SI 2026/896), which was made on 29 July 2026, laid before Parliament on 30 July, and comes into force on **27 August 2026**. It amends **Part 14 (renewable energy) of Schedule 2** to the 2015 GPDO — the part that grants planning permission for certain solar installations without the need for a planning application. The headline structural change is that the rules for **dwellinghouses** and for **blocks of flats** have been separated out and set down explicitly, where the old text bundled them together. On top of that, the order adds a set of clearer dimensional limits and — the genuinely new bit — a definition and rules for plug-in solar. ## Solar on houses: the new limits For solar PV or solar thermal on a **dwellinghouse** (Class A), the order spells out when an installation falls *outside* permitted development and therefore needs a planning application. The limits to have in mind: - **On a wall:** not permitted if the equipment protrudes more than **0.2 metres** beyond the wall where that wall abuts a highway, or more than **0.4 metres** in any other case. - **On a balcony or roof enclosure:** the same 0.2 m (fronting a highway) / 0.4 m (otherwise) protrusion limits. - **On a pitched roof:** not permitted if it protrudes more than **0.2 metres** beyond the roof slope, or if the highest part sits above the ridge (excluding the chimney). - **On a flat roof:** not permitted if the highest part is more than **0.6 metres** above the highest part of the roof (excluding the chimney). - **Heritage constraints:** in a conservation area or World Heritage Site, not permitted on a wall, balcony or roof enclosure that fronts a highway; and not permitted at all on a scheduled monument or on a **listed** dwellinghouse. **Stand-alone** (ground-mounted) solar in the curtilage (Class B) gets its own height table — ranging from **1 metre** where it sits forward of the principal elevation and within 5 m of the boundary, up to **4 metres** in the most unconstrained case — plus a cap keeping the panel area to no more than **9 square metres**, and a new **prior-approval** step for stand-alone solar placed on article 2(3) land within 5 m of the boundary. ## Plug-in "balcony" solar is now in the rules The most talked-about change is the arrival of **plug-in solar** — defined in the order as solar PV "intended for connection to the relevant domestic premises' electricity installation by means of a standard plug and socket". It's now folded into the definition of solar PV, which brings the plug-in, stand-it-on-your-balcony kits that are common across Europe into the English PD framework as they become legal to self-install here. There's an important safety-driven limitation, though: plug-in solar is **not** permitted development where any part of it would be installed on a **wooden wall, balcony, fence, gate or enclosure**, or on a **timber-clad** part of a house or block of flats. So the combustible-substrate carve-out that assessors already recognise from other parts of the regs shows up here too. ## The one-year grace period If you have a scheme or product that was permitted under the old wording but no longer qualifies under the new rules, the order includes a **transitional provision**: previously permitted development can still be carried out until the **end of 26 August 2027**. That gives roughly a year of overlap rather than a hard cliff-edge — useful if something is already designed and in the pipeline. ## Why this matters for Part L and the Future Homes Standard This is a planning change, not a Building Regulation — but it lands right next to the energy work we do. Under the **Future Homes Standard**, on-site solar PV is a central part of how new homes hit their Part L targets; the FHS notional dwelling assumes a meaningful area of roof-mounted PV. So the PD rules that govern where and how PV can go on a roof, a wall or the ground directly shape what's deliverable on a plot without a separate application — and, by extension, how easily a design reaches compliance. The practical takeaways are straightforward: if you're specifying roof or wall-mounted PV, sense-check the new protrusion and ridge-height limits early so the array you're relying on for the Part L result is actually permitted development; watch the heritage and listed-building carve-outs on constrained sites; and if plug-in kit is in the mix, keep it off timber substrates. Solar is only ever one lever in the Part L calculation — the fabric, glazing and thermal-bridging numbers have to be right underneath it, or the PV ends up compensating for losses you could have designed out. If you'd like the fabric and **PSI-value** side modelled properly so your renewables aren't papering over a weak envelope, [get in touch](/contact/) and we'll tell you how we'd approach it. *Sources: [The Town and Country Planning (General Permitted Development) (England) (Amendment) Order 2026 (SI 2026/896), legislation.gov.uk](https://www.legislation.gov.uk/uksi/2026/896/made) · [Explanatory Memorandum to SI 2026/896, legislation.gov.uk](https://www.legislation.gov.uk/uksi/2026/896/memorandum/contents) · [Town and Country Planning (General Permitted Development) (England) Order 2015, Part 14 of Schedule 2, legislation.gov.uk](https://www.legislation.gov.uk/uksi/2015/596/schedule/2/part/14)* --- # Scotland's 'Passivhaus equivalent' standard slips to 2029 — what the Stage 2 consultation proposes URL: https://energycount.co.uk/news/scotland-passivhaus-equivalent-stage-2-consultation/ Date: 2026-08-13 This one is for our Scottish readers first — but anyone tracking where UK new-build standards and the Home Energy Model are heading should take a look. On **24 July 2026** the Scottish Government published its **Stage 2 consultation** on the next revision to Scotland's energy standards, part of its work to introduce a **'Passivhaus equivalent'** standard for new homes through the Building Standards. The most immediate headline is a slipped timetable; the more interesting detail is what's proposed underneath. ## The date has moved: autumn 2029, not 2028 The earlier Stage 1 partial response pointed to the new standards coming into force on **31 March 2028**. That's now moved. After reviewing the programme and the time needed to develop the supporting guidance, assessment methodologies and software, the Scottish Government intends to publish guidance and approved methodologies for **Standard 6.1 in autumn 2027**, with the new requirements now expected to take effect in **autumn 2029**. It's also keeping its options open on *how* the standard lands — whether in full, in phases, or as a voluntary route before it becomes mandatory. ## Three options for the energy uplift The consultation sets out three routes for future energy performance: - **Good Practice** — roughly a **6% cut** in carbon emissions against the current 2023 standards. Improved fabric, typically with an air source heat pump; PV required where an alternative heating system (such as direct electric or a heat network) is used. - **Best Practice** — roughly a **37% cut** in carbon emissions. A bigger step up in fabric performance plus **mechanical ventilation with heat recovery (MVHR)**, and PV alongside a heat pump. - **Current Standard** — retain the existing 2023 requirements, with no uplift. Both of the uplift options strengthen the fabric; the Best Practice route is the more demanding, bringing in MVHR and, with a heat pump, PV. ## New metrics and a HEM-based method Compliance would be judged on two metrics: a **Delivered Energy Rate** (energy delivered to the home, excluding unregulated use and grid exports) and a **Space Heat Demand Rate** (driven by fabric performance — insulation, **thermal bridging** and airtightness). If that second metric sounds familiar, it should: it puts fabric and junction detailing right at the heart of compliance. On calculation, Standard 6.1 will be based on the **Home Energy Model with a Scottish wrapper** — the same underlying engine England is moving towards, tailored for Scotland. A modified version of the **Passivhaus Planning Package (PHPP)** is also proposed as an approved compliance methodology. The current SAP 10.2 notional-dwelling approach to setting targets would be replaced with a series of **target performance tables**, selected by the home's location, dwelling type, orientation and heating system. ## Fabric and overheating The maximum backstop U-values in Standard 6.2 would stay unchanged, but a new maximum **air permeability of 5 m³/(h·m²) at 50 Pa** would be introduced — so every new home would need an airtightness test at or below that level. On overheating, the Government is reviewing Standard 3.28 and considering whether PHPP could be used to assess overheating risk, with updated guidance to follow. ## Why it's worth reading in England too Scotland and England run separate Building Standards, so none of this applies to an English Part L job. But the direction of travel is shared — HEM as the calculation engine, fabric-led metrics, tighter airtightness and a hard look at thermal bridging — and Scotland is arguably setting out its stall in more detail. If you work across the border, or you want a preview of the arguments likely to shape future English uplifts, it's a useful read. The consultation **closes on 16 October 2026**. Whichever standard you're working to, the common thread is fabric: tighter airtightness targets and a fabric-driven space-heat metric both reward getting the junctions and PSI-values right at design stage. If you'd like your thermal bridging and fabric performance modelled properly — in Scotland or England — [get in touch](/contact/) and we'll tell you how we'd approach it. *Sources: [Scottish building regulations: proposed changes to energy and environmental standards — Stage 2 consultation, gov.scot](https://www.gov.scot/publications/scottish-building-regulations-proposed-changes-energy-environmental-standards-stage-2-consultation-bria/) · [Stage 2 consultation (consult.gov.scot)](https://consult.gov.scot/local-government-and-housing/building-regulations-passivhaus-equivalent-stage-2/) · [Elmhurst Energy: Scottish Government outlines revised timeline in Stage 2 building regulations consultation](https://www.elmhurstenergy.co.uk/blog/2026/08/07/scottish-government-outlines-revised-timeline-in-stage-2-building-regulations-consultation/)* --- # The government just backed measuring how homes really lose heat URL: https://energycount.co.uk/news/smeter-strategic-guide-measured-performance/ Date: 2026-08-13 Most of what we do rests on *modelled* performance — SAP, HEM, U-values and PSI-values that predict how a home should behave. This month the government put its weight behind measuring how a home *actually* behaves. The Department for Energy Security and Net Zero (DESNZ) has published a **Smart Meter Enabled Thermal Efficiency Ratings (SMETER) Strategic Guide**, along with a supporting evidence base and case studies. It won't change a compliance calculation tomorrow, but it's a clear signal of where things are heading. ## What SMETER actually measures A SMETER assessment looks at how well an *occupied* home holds onto heat. Most methods combine actual energy-use data, indoor and outdoor temperatures and local weather to work out how quickly heat escapes the building. The result is expressed as a **Heat Transfer Coefficient (HTC)** — in watts per kelvin — for the whole dwelling. The rule of thumb is simple: a **high HTC** means the home is leaking heat quickly, while a **low HTC** means it's retaining heat well. Crucially, this is a measured, in-use figure rather than a value derived from construction assumptions. To be clear about what it is *not*: a SMETER assessment does not replace an EPC or a detailed survey. It sits alongside modelled assessments, giving real-world evidence of how a building performs against how it was predicted to perform. ## Why this matters: the performance gap For years, decisions about energy efficiency have leaned on modelled assessments and assumptions about how a building was built. Those models remain essential — but hidden defects, unknown or missing insulation and air leakage all mean the real building can behave differently from the one on paper. The difference between predicted and measured performance is the **performance gap**, and it's exactly the thing measured HTC can expose. The guide's evidence base is the interesting part. It highlights the **MEASURED project** — a field trial run by Build Test Solutions, Veritherm UK and Elmhurst Energy across 56 homes — which tested whether measured heat loss could improve heat-pump surveys and design. The headline finding is striking: the traditional heat-loss calculation matched the measured result in only **30%** of homes. It **over**estimated heat loss in 59% of cases and **under**estimated it in 11%. In other words, for roughly **70%** of the homes, relying on the standard BS EN 12831 calculation alone could have led to a heat pump being sized incorrectly. That's a useful reminder for anyone specifying low-carbon heating under the Future Homes Standard: oversized kit costs more and can run inefficiently, while undersized kit leaves homes cold. Measured data offers a way to sense-check the assumptions. ## An important caveat Measured HTC tells you *how much* heat a building is losing overall — not *where* it's being lost. So it's best used to calibrate and strengthen detailed, room-by-room calculations, not to replace the wider heating-design process. If the number looks off, the follow-up is the familiar toolkit: airtightness testing, thermal imaging and in-situ U-value measurement to pin down where the losses actually are. ## Where it's heading — EPCs and policy This is where assessors should pay attention. The government has consulted on a **voluntary option to record validated, quality-assured SMETER HTC values on future EPCs**, alongside an HTC produced by the Home Energy Model, and is analysing the responses. DESNZ is also building the validation and quality-assurance systems that measured performance would need, and has signalled interest in using SMETER within future policy, including the Warm Homes Plan. None of that makes measured HTC a general requirement today. But taken together with **CIBSE TM71** — the new framework for measuring and reporting HTC values across different methods — it points to a future where calculated and measured figures are used side by side: the model for a consistent assessment framework, the measurement for evidence of how a specific home really performs. With smart meters now in most homes, the raw data is already there. ## What to do with this now There's nothing to comply with yet, so treat this as horizon-scanning rather than a deadline. The practical takeaways: expect measured performance to feature more heavily in retrofit funding, quality assurance and eventually EPCs; be ready for clients to ask how a modelled result compares with real-world data; and remember that a strong measured HTC still comes down to the fundamentals — fabric, airtightness and well-detailed junctions. That last point is the one we'd flag hardest. Measured performance will increasingly hold designs to account, and the homes that measure well are the ones where the thermal bridging and fabric detailing were right on paper first. If you'd like your **PSI-values and fabric performance** modelled properly so the as-built numbers stand up to real-world measurement, [get in touch](/contact/) and we'll tell you how we'd approach it. *Sources: [Smart-meter-enabled thermal efficiency ratings (SMETER): Strategic Guide, GOV.UK](https://www.gov.uk/government/publications/smart-meter-enabled-thermal-efficiency-ratings-smeter-strategic-guide) · [SMETER case studies and evidence base annex, GOV.UK](https://assets.publishing.service.gov.uk/media/6a4790e28effd97622f53c04/smeter-case-studies-evidence-base-annex.pdf) · [CIBSE TM71: Measuring Heat Transfer Coefficients in Buildings (2026)](https://www.cibse.org/knowledge-research/knowledge-portal/tm71-measuring-heat-transfer-coefficients-in-buildings-2026/) · [Elmhurst Energy: New SMETER guidance — from measurement to action](https://www.elmhurstenergy.co.uk/blog/2026/08/11/new-smeter-guidance-from-measurement-to-action-the-future-of-measured-building-performance/)* --- # Biodiversity Net Gain just got lighter for small sites — what changed on 6 August URL: https://energycount.co.uk/news/biodiversity-net-gain-exemptions-6-august-2026/ Date: 2026-08-10 This one isn't a SAP input, but it lands on the same desks we work with every day — housebuilders, small developers and the planning teams around them. On **6 August 2026** a first batch of changes to **Biodiversity Net Gain (BNG)** came into force in England, and if you bring forward smaller sites, the paperwork just got lighter. ## The quick recap on BNG Since February 2024, most developments needing planning permission under the Town and Country Planning Act have had to deliver a **10% biodiversity net gain** — leaving habitat measurably better than before, on-site where possible, or off-site or via statutory credits where not. It's been a real workload for small schemes in particular, where the assessment cost can be out of proportion to the site. The government consulted on easing that burden last year, responded in **April 2026**, and has now made the first legislative changes through **The Biodiversity Gain (Town and Country Planning) (Amendment) Regulations 2026 ([SI 2026/790](https://www.legislation.gov.uk/uksi/2026/790/contents/made))**, laid before Parliament on 13 July and in force from 6 August ([Defra Environment blog, 14 July 2026](https://defraenvironment.blog.gov.uk/2026/07/14/biodiversity-net-gain-amendments-and-transitional-arrangements-published/)). ## What actually changed on 6 August Four things, per Defra's confirmation: - **A new 0.2-hectare exemption.** The smallest developments — sites of 0.2 ha or less — no longer have to do mandatory BNG, *unless* on-site priority habitat would be negatively impacted. This is the headline: it takes a large slice of minor applications out of the regime entirely. - **A new temporary-development exemption.** Development on land that will be reinstated within five years or less is exempt — again, unless on-site priority habitat is negatively impacted. - **A relaxed hierarchy for minor development.** Minor sites that *aren't* exempt (for example, those over 0.2 ha) can now go straight to off-site provision in the first instance, rather than having to work through the on-site-first hierarchy. - **The self- and custom-build exemption is removed.** The old blanket carve-out for self- and custom-build is gone. Those projects now sit under the ordinary rules — so a small self-build may instead pick up the new 0.2-hectare exemption, but it isn't exempt simply for being self-build. Defra is clear that exempt developments are still expected to incorporate nature-friendly features, and that existing environmental protections and the planning mitigation hierarchy continue to apply — permission should still be refused where significant harm to biodiversity can't be avoided, mitigated or, as a last resort, compensated ([updated Planning Practice Guidance](https://www.gov.uk/guidance/biodiversity-net-gain-exempt-developments)). ## The date that matters: applications from 6 August This is the bit to get right. The changes apply **only to new applications for planning permission made from 6 August 2026**. Anything already submitted before that date continues under the existing BNG rules — the exemptions don't retro-apply. So the question for any given scheme is simply: when was (or will) the application be made? ## What's still coming This is a first batch, not the whole reform. Defra has signalled further changes to follow from the April response, including exemptions for development whose primary purpose is to conserve or enhance biodiversity, a targeted exemption for works to parks, playing fields and public gardens, and updates to the **statutory biodiversity metric**. Separately, the consultation on a possible exemption for certain residential **brownfield** development closed on 10 June 2026, with a government response still to come. In short: more movement to expect, but nothing else in force yet. ## What this means for you If you advise on or appraise smaller residential sites, it's worth re-checking your live pipeline against the 0.2-hectare threshold and the application date — some schemes that were budgeting for BNG assessment and units may no longer need them, while anything already in the system stays as it was. And keep priority habitat front of mind: it's the condition that switches every one of these exemptions off. Working on the environmental side of a stalled or marginal site? Our nature and nutrient tools can help you scope obligations before you commit spend — [take a look here](/tools/). --- # The EPC is being rebuilt — four metrics, and the Home Energy Model behind it URL: https://energycount.co.uk/news/reformed-epcs-four-metrics-home-energy-model/ Date: 2026-08-09 The Energy Performance Certificate has looked more or less the same for years: one coloured dial, one A–G band, one number that's meant to sum up a whole building. That's about to change. The government has confirmed a wholesale reform of the domestic EPC — a move from a single headline rating to **four separate metrics**, produced by the **Home Energy Model (HEM)** rather than RdSAP. ## What's actually changing In its partial response to the Energy Performance of Buildings consultation (updated **9 March 2026**), the Ministry of Housing, Communities and Local Government confirmed that domestic EPCs will replace the current single cost-based headline with **four headline metrics** ([GOV.UK, partial government response](https://www.gov.uk/government/consultations/reforms-to-the-energy-performance-of-buildings-regime/outcome/reforms-to-the-energy-performance-of-buildings-regime-partial-government-response)): - **Energy cost** — an estimate of running costs, the nearest thing to today's headline. - **Fabric performance** — a measure of the building envelope that doesn't move with energy prices; effectively a proxy for how well a home holds its heat. - **Heating system** — a rating reflecting the efficiency and carbon intensity of the heat source, rewarding a move to low-carbon heating. - **Smart readiness** — how well the home can work with smart meters and flexible tariffs. Sitting behind those, the certificate will also carry a secondary **energy demand** figure (based on delivered energy) and a secondary **carbon** metric. To keep comparisons possible during the switchover, the legacy Energy Efficiency Rating stays on the certificate for now. Non-domestic EPCs are treated differently: they keep the single carbon-based **Environmental Impact Rating** as their headline. The thinking is straightforward. One number was always doing too much work — a cost metric penalises electric heating on price, blurs fabric quality, and shifts with the energy market. Splitting it out gives owners a clearer, fabric-first picture: insulate well, then electrify. ## The bit that matters to assessors: HEM produces it This isn't just a redesign of the certificate. Reformed domestic EPCs are intended to be **generated using the Home Energy Model**, through a separate DESNZ consultation on how new-style EPCs will be produced and how the four metrics will be banded. For existing homes, that points to a more **modular** approach to assessment than the RdSAP data set you use today. If you've been watching HEM purely as the SAP replacement for new-build compliance, this is the other half of the story — HEM is also the engine intended to sit under the domestic EPC. The current RdSAP-based system remains the only route for existing-dwelling EPCs until the reformed methodology goes live. ## When Originally the government wanted new-style EPCs from **October 2026**. On 9 March 2026 that was pushed back: the launch now moves to the **second half of 2027**, with government committing to agree a specific date and a **shared implementation plan** with industry and the devolved administrations **by summer 2026**. So the plan itself is due about now — worth keeping an eye on. A final consultation response, covering the remaining questions (EPC data, EPC quality, DEC validity periods and more), is still expected during 2026. ## A few other changes worth banking Alongside the metrics, the response confirmed some practical points that will land on assessors and agents: - The **10-year validity period** is retained for both existing and reformed EPCs. - An EPC will be required at the **point of marketing** a property, not up to 28 days after — so the certificate needs to be in hand before a home goes on the market. - Scope widens: a valid EPC for the **whole HMO** when a single room is let, EPCs for **short-term lets** regardless of who pays the bills, and the **heritage exemption** removed. And the deadline that gives all this its edge hasn't moved: the private-rented MEES **EPC C by 2030** target still stands, which compresses the window between the new methodology arriving and landlords having to meet it. ## What to do now Nothing changes on your current EPCs today — anything issued now stays valid for ten years, well past 2030. But the direction is set: a four-metric certificate, produced by HEM, with fabric performance pulled out as a headline in its own right. If you assess existing homes, this summer's implementation plan is the one to watch, and it's a good moment to get comfortable with HEM's approach before the retraining rush. We'll keep tracking the reform as the implementation plan and final response land. If you'd like the plain-English version of each step as it happens — and a heads-up on what it means for your assessments — keep an eye on the Energycount news feed. --- # TM59 has been rewritten — what the 2026 overheating methodology changes URL: https://energycount.co.uk/news/cibse-tm59-2026-overheating-update/ Date: 2026-08-08 Overheating has been quietly climbing up the design agenda for years, and this month it took a big step. In **July 2026**, CIBSE — working with Arup and Loughborough University — published a substantially revised second edition of **TM59**, the standard methodology for assessing overheating risk in homes. It's been retitled *Overheating Risk in Dwellings: A Design Stage Methodology*, and it's less a refresh than a rewrite. ## Why TM59 matters to assessors If you touch Part O, you already know TM59. **Approved Document O** offers two compliance routes — a simplified prescriptive check, and the dynamic thermal modelling route built on TM59. Where a design can't pass the simplified method (and plenty can't), the TM59 model is what decides whether a home overheats on paper. So a new edition of the methodology changes the reference point for a large slice of overheating work. ## What's actually changed The headline is a shift to a **passive-first, three-stage assessment**. The 2017 edition was essentially a pass/fail check against the criteria. The 2026 edition makes you demonstrate the design in a strict hierarchy: **Stage 1** assesses the dwelling under an unconstrained passive scenario; **Stage 2** only allows enhanced mechanical ventilation where real site issues — external noise, poor air quality, security — genuinely restrict opening windows; and **Stage 3** treats mechanical cooling as a last resort. It's the same cooling hierarchy London assessors will recognise from the GLA's energy guidance. The number of assessment criteria has grown from two to **four**. Criterion A covers daytime comfort in naturally ventilated living rooms, kitchens and bedrooms — and now home offices. Criterion C formalises the rules for mechanically ventilated or cooled spaces. And a new **Criterion D makes communal circulation areas a mandatory part of compliance**, requiring them to stay below 28°C for all but 3% of occupied hours — previously a flagged risk, now a potential fail. The biggest technical change is the **bedroom night-time test (Criterion B)**. The old rule failed a bedroom if it exceeded 26°C for more than 1% of annual sleeping hours. The new method instead counts **overheated nights** — a maximum of four between May and September — using mean operative temperature, with sleeping hours shifted to 11pm–8am and thresholds that vary by occupant category. It's backed by Loughborough University sleep research, and it's designed to reflect real disruption rather than a blunt hourly count. A few other changes worth noting: **ceiling fans** are now formally recognised as a mitigation measure, with specified air speeds and temperature uplifts (though not for sleeping bedrooms or communal circulation, and with rules to stop double-counting in the model); a dedicated **home office** occupancy profile has been added; the scope now explicitly extends to sheltered housing, care homes, student accommodation, hotels, hospital bedrooms and even retrofit projects; and the reporting requirements are considerably more detailed, expecting you to document and justify every stage, occupant category and ventilation or shading assumption. ## The bit that trips people up: the regs haven't caught up Here's the nuance that matters for compliance. **TM59:2026 is a CIBSE methodology, not a Building Regulation.** Approved Document O 2021 — in force since 15 June 2022 — still references the **2017** edition of TM59. The government confirmed in its March 2026 Future Homes Standard consultation response that Part O will get a **full technical review**, and adopting the updated TM59 is explicitly on that review's list — but no revised Approved Document O and no date have been published yet. So there's a genuine gap to manage. For strict Building Regulations sign-off, the 2017 methodology remains the referenced document until Part O is revised. But the 2026 edition is now the current industry best practice, and London schemes, planning conditions and many clients' own standards will increasingly expect it. On a lot of projects you'll effectively be working to both — which makes it worth reading the new edition now rather than when the regs finally point at it. ## What this means for design The direction of travel is clear and it rewards the same things good assessors already push for: real passive design, effective external shading, sensible glazing ratios and genuine thermal mass, rather than a marginal pass that leans on opening windows at night on a noisy or insecure elevation. Designs built on those assumptions will weather the transition — and any future Part O revision — a lot better than those that don't. There's a knock-on into the energy calculation, too. Where a scheme leans on reduced g-value glazing or mechanical cooling to pass overheating, that choice shows up in the **Part L** numbers — one more reason to get the fabric and glazing strategy right early, before it's fighting your SAP result. If overheating is the sticking point on one of your sites, or you want the fabric, glazing and thermal-bridging side modelled properly so it doesn't undermine your Part L result, [get in touch](/contact/) and we'll tell you how we'd approach it. *Sources: [CIBSE TM59 — Overheating risk in dwellings: a design stage methodology (2026), CIBSE Knowledge Portal](https://www.cibse.org/knowledge-research/knowledge-portal/tm59-overheating-risk-in-dwellings-a-design-stage-methodology-2026/) · [TM59:2026 — Overheating in Residential Buildings; what's changed, Housebuilder & Developer, 17 July 2026](https://www.hbdonline.co.uk/news/tm59-2026-overheating-in-residential-buildings-whats-changed-from-the-2017-edition/) · [Guidance to help tackle overheating risk in homes, Loughborough University, July 2026](https://www.lboro.ac.uk/news-events/news/2026/july/overheating-homes/) · [Government Confirms Full Review of Approved Document O (HEM Guide, 9 April 2026, verified against the FHS consultation response)](https://home-energy-model.co.uk/news/2026-04-09-part-o-overheating-review/) · [Approved Document O, Overheating (gov.uk)](https://www.gov.uk/government/publications/overheating-approved-document-o)* --- # The Building Safety Levy goes live on 1 October — what developers and Building Control need to know URL: https://energycount.co.uk/news/building-safety-levy-1-october-2026/ Date: 2026-08-08 This one isn't a SAP input, but it lands squarely on the desks of the people we work with every day — housebuilders, developers and Building Control. On **1 October 2026** the **Building Safety Levy** comes into operation in England, and if you're bringing forward anything of ten homes or more, it's a number you'll want in your appraisal now rather than as a surprise near completion. ## What the levy is The Building Safety Levy is a tax on new residential buildings in England, brought in under the **Building Safety Act 2022**. The money raised — expected to run to billions of pounds over the next decade — goes towards fixing building safety defects such as unsafe cladding across the country. Crucially, it's collected by **local authorities**, in their role as the local guardians of the building control process, rather than by a new national body. The rules sit in **The Building Safety Levy (England) Regulations 2025** (made on 19 November 2025), with a set of minor amendment regulations laid before Parliament on 2 July 2026 and the official guidance last updated in July 2026. ## Who pays, and who doesn't The levy bites where three conditions are all met: the works form part of a **major residential development**, they create new residential floorspace, and the client isn't an exempt person. "Major residential development" means **10 or more new dwellings, or 30 or more bedspaces** in purpose-built student accommodation. Schemes below that threshold are outside the levy altogether — and you can't dodge it by slicing a large permission into sub-ten-dwelling building control applications, because liability follows the planning permission for the wider site. A number of developments are excluded. **Social housing** (including affordable, social and intermediate rent, shared ownership, and First Homes sold at no more than 70% of market value) and **supported housing** are exempt, as is anything built by a **non-profit registered provider of social housing** — for those providers, all their works are exempt even where the homes would otherwise be chargeable. Also outside the charge: care homes and hospices, hospitals, hotels and hostels, children's homes, refuges for domestic abuse victims, armed forces accommodation and similar. Straightforward extensions and improvements that don't create a new dwelling aren't caught either. ## How the charge is worked out The levy is a **rate per square metre** applied to the chargeable floorspace, measured as Gross Internal Area under the RICS Code of Measuring Practice. Each local authority has its own rate, weighted by average house prices in the area — so the figures vary enormously, from around £13 per square metre in the lowest-value areas to over £100 per square metre in the priciest. There's a **50% discount for previously developed ("brownfield") land**, to reflect the higher cost of building there. It's worth actually pulling your council's rate from the published schedule before you price a scheme, because on a site of any size the difference between a low-value and a high-value authority is real money. ## Where the teeth are Here's the bit to flag to your commercial team: payment is due **before the earlier of completion or occupation**, and it's enforced through the certificate you can't do without. If the levy isn't paid, the building control authority will **withhold the completion certificate** (or reject the final certificate). No certificate, no sign-off — so this isn't a bill you can leave to argue about later. One point of timing relief: the levy only applies to applications for building control approval submitted **on or after 1 October 2026**. Applications submitted before that date aren't caught, even if they're varied afterwards — but if a pre-October application is rejected and then resubmitted after the go-live, it will be liable. ## What we'd suggest doing If you've got schemes crossing the 1 October line, three quick jobs are worth doing now: check your local authority's rate against the published schedule, confirm whether any part of the scheme qualifies for the social-housing or brownfield reliefs, and make sure whoever manages your building control applications knows the levy has to be cleared before the completion certificate is issued. The levy sits alongside the compliance work we do help with — the **Part L**, **Part G** and thermal-bridging numbers that also have to be right before Building Control signs a scheme off. If you'd like a hand getting the energy and water side buttoned down while the commercial team handles the levy, [get in touch](/contact/) and we'll tell you how we'd approach it. *Sources: [Building Safety Levy: Guidance — Section 1: Introduction (gov.uk, updated July 2026)](https://www.gov.uk/guidance/building-safety-levy-guidance/section-1-introduction) · [Building Safety Levy: Guidance — contents (gov.uk)](https://www.gov.uk/guidance/building-safety-levy-guidance) · [The Building Safety Levy (England) Regulations 2025 (legislation.gov.uk)](https://www.legislation.gov.uk/uksi/2025/1236/contents/made)* --- # A water label for taps and showers is coming — and it lands next to Part G URL: https://energycount.co.uk/news/mandatory-water-efficiency-labelling-2026/ Date: 2026-08-07 You already read a lot of labels: SAP bands, energy ratings, the U-value on a window schedule. There's a new one on the way, and this time it's on the fittings themselves — the taps, showers and WCs that decide whether your Part G calculation passes. The government is introducing a **mandatory water efficiency label**: an A–F, colour-coded rating — much like the energy label on a fridge — that has to be shown on water-using products at the point of sale. ## What's actually being introduced The scheme is the **Mandatory Water Efficiency Labelling Scheme (MWELS)**, brought in under powers in the Environment Act 2021. In short, it puts a standard, comparable water-efficiency rating on the products people buy. The headline points: - A single **A–F colour-coded label** showing how much water a product uses, so two showers or two WCs can be compared like for like. - It covers the usual suspects — **taps, showers, toilets and urinals, dishwashers and washing machines**. - The obligation sits with the trade: **suppliers** test their products, work out the banding and produce the label; **dealers** (retailers and merchants) have to display it clearly at the point of sale. - It's built on the international standard **ISO 31600:2022**, and it applies **UK-wide** — England, Scotland, Wales and Northern Ireland. The reasoning is the same one driving the Part G reform: England is short of water, and demand from new homes has become a genuine constraint on where and how much you can build. A label won't save a drop on its own, but it makes the efficient choice the obvious one on the shelf. ## Where it stands right now This is coming, not here. The regulations were **laid before Parliament on 6 May 2026** as a draft affirmative instrument — meaning both Houses have to approve them before they take effect — with the intention of the scheme **coming into force by the end of 2026**. So nothing changes on your current jobs today. But the direction is set, and the timing is worth noting: the label is arriving in the same window as the proposed cut to the Part G standard from **125 to 105 litres per person per day**. Two separate pieces of policy, pointing the same way, landing at roughly the same time. ## It's not landing without argument Worth being straight about: the industry isn't uniformly behind the detail. The **Builders Merchants Federation** has flagged the risk of consumer confusion, given there's already an established voluntary label (the Unified Water Label) in the market — and a second, mandatory scheme sitting alongside it could muddy rather than clarify. Appliance manufacturers have raised concerns about cost and about whether a single metric fairly represents how products like dishwashers actually perform. There's a deeper point too, and it's one assessors will recognise. A recent University of Surrey study (with input from Mira Showers) made the case that **flow rate on a label doesn't equal real-world consumption**: push flow rates too low and people take longer showers, or tamper with the fitting, and the saving the label promised quietly disappears. The label tells you what a product can do, not what a household will actually do with it — which is exactly the gap the Part G calculator's fixed-use assumptions try, imperfectly, to bridge. ## What it means for you For assessors and specifiers, the useful bit is the join between this and Part G. The water calculator has always run off the specified fittings — shower flow rate, bath capacity, WC flush volume, tap flow rates. A consistent, mandatory label makes those inputs **easier to source and easier to evidence**: instead of digging through manufacturer datasheets for a flow rate, you'll increasingly have a standard rating to point to. It also sharpens the compliance question that Defra has already raised — whether the fittings on the drawings are the fittings that actually get installed. When every product on site carries a visible rating, the gap between the specified spec and the fitted spec gets harder to hide. None of this changes your method today. **125 l/p/d remains the standard you calculate to**, with 110 l/p/d where a Local Plan requires it, until the Part G reform is confirmed. But if you're specifying fittings for schemes that will complete in 2027 and beyond, it's worth getting into the habit now of choosing products on their water rating — because the margin between a comfortable pass and a fail lives entirely in those numbers. ## What we'd suggest doing Know your number before the standards tighten. Run your standard house types through a proper Part G calculation and see which ones still pass with headroom — a fittings spec is far cheaper to adjust on paper than after a Building Control inspection. **WaterMonkey** does exactly that: the full official water efficiency methodology, live PASS/FAIL as you type at 125 or 110 l/p/d, rainwater and greywater included, free in your browser. Building Control-ready PDF reports are £25 +VAT, and one dwelling type covers every identical plot on a site — so a whole estate needn't cost the earth. We'll factor the new labelling in as the scheme and the revised Part G methodology are confirmed. [Try WaterMonkey →](/tools/part-g-water-calculator/) If water is already the sticking point on one of your sites, [get in touch](/contact/) and we'll tell you how we'd approach it. *Sources: [UK mandatory water efficiency labelling — Defra consultation and outcome (gov.uk)](https://www.gov.uk/government/consultations/uk-mandatory-water-efficiency-labelling) · [United Kingdom: New Mandatory Water Efficiency Labelling (MWEL) Regulations — Product Compliance Institute, 6 February 2026](https://www.productcomplianceinstitute.com/2026/02/06/united-kingdom-new-mandatory-water-efficiency-labelling-mwel-regulations/) · [The Mandatory Water Efficiency Labelling (MWEL) Regulations 2026 — TÜV Rheinland](https://www.tuv.com/regulations-and-standards/en/united-kingdom-the-mandatory-water-efficiency-labeling-mwel-regulations-2026.html) · [Water efficiency labelling alone won't deliver Britain's water-saving ambitions — Builders Merchants Journal, 27 July 2026](https://buildersmerchantsjournal.net/water-efficiency-labelling-alone-wont-deliver-britains-water-saving-ambitions/)* --- # Part G is heading for 105 litres — and the water industry has backed it URL: https://energycount.co.uk/news/part-g-105-litres-water-efficiency/ Date: 2026-08-06 If you've done a Part G water calculation in the last decade, you know the number: **125 litres per person per day**. It's been the baseline since the standard came in, with an optional tighter standard of 110 l/p/d that councils can require through their Local Plans in water-stressed areas. Both figures are on the table — and this month the water industry came out publicly in favour of changing them. ## What's actually proposed Defra's [review of water efficiency standards in the Building Regulations 2010](https://consult.defra.gov.uk/water-efficiency-demand/review-of-water-efficiency-standards) put forward three changes: - Cutting the minimum Water Efficiency Standard from **125 l/p/d to 105 l/p/d** - Cutting the optional technical standard from **110 l/p/d to 100 l/p/d**, for areas of water stress or other local need - **Revising the water calculator and the fittings-based approach**, to reflect how water use and fitting technology have moved on since the standard was written There's also a call for evidence attached, looking at whether rainwater harvesting and grey/black water reuse should play a bigger role in future. The driver is blunt, and it isn't really about the environment: water scarcity has become a housing supply problem. Defra's own consultation puts it in cash terms — failing to manage water demand could mean **over 61,000 homes not being built** this parliamentary term, at a cost of some £25 billion. Cambridge and parts of Sussex have already seen schemes held up because demand outstripped supply. Twenty litres per person per day, multiplied across a site, is the difference between a scheme that fits inside the water resource envelope and one that stalls. ## Where it stands right now The consultation opened on **23 September 2025** and closed on **16 December 2025**. Defra has not yet published its response, so nothing in Approved Document G has changed: **125 l/p/d remains the standard you design and calculate to today**, with 110 l/p/d where a Local Plan policy or planning condition requires it. The stated intention is to implement the Part G changes **during 2026**, subject to the consultation outcome and parliamentary approval, followed by a **six-month transitional period** ([CIH briefing, September 2025](https://www.cih.org/news/cih-briefing-on-defra-s-consultation-on-updating-part-g-of-the-building-regulations-on-water-efficiency-in-new-homes/)). The news this month is **Water UK** — the industry's trade association — publishing its response backing the 105 l/p/d figure. It also supports the fittings-based route to demonstrating compliance as simpler and more consistent, and argues for a **single national standard** rather than a patchwork of locally set numbers ([Water Magazine, 3 August 2026](https://www.watermagazine.co.uk/2026/08/03/water-uk-backs-tougher-water-efficiency-standards-for-new-homes/)). If ministers agree, that last point would be a quiet relief to anyone who's had to work out which of three water policies a particular district council is currently applying. Water UK's caveat is worth noting too: tighter new-build standards alone won't deliver the demand reductions England needs — retrofit, smart metering and more efficient appliances have to do the heavy lifting on the existing stock. Useful context for how this is likely to be framed when the response lands. ## What it means in practice The jump from 125 to 105 isn't enormous, but it's enough to bite on schemes that currently scrape through. If you've been passing at 118 or 120 with a fairly standard fittings spec, that margin disappears. The pressure lands where it always does: **shower flow rate, bath capacity, WC flush volumes, and basin and kitchen tap flow rates**. A generous bath and a 9 l/min shower head will eat the new headroom between them without any help. The other lever is rainwater or greywater reuse, which the calculator already recognises — and which the call for evidence suggests the government is interested in leaning on harder in future. There's a compliance angle too. The consultation notes that actual consumption in some new homes runs as high as **195 l/p/d** — either because people use water in unexpected ways, or because dwellings aren't being built to the standard on the drawings. Expect more attention on whether the fittings that were specified are the fittings that got installed. ## What we'd suggest doing Don't redesign anything yet. Do know your number. Run your standard house types through the calculation and see which ones would still pass at 105. One dwelling type covers every identical plot on a site, so this is a small piece of work that tells you a lot about your exposure — and it's far cheaper to fix a specification on a spec sheet than after a Building Control inspection. **WaterMonkey** does exactly that: the full official water efficiency methodology, with live PASS/FAIL as you type at 125 or 110 l/p/d, rainwater and greywater included, free in your browser. Building Control-ready PDF reports are £25 +VAT, and one dwelling type covers every identical plot on the site — so a whole estate needn't cost the earth. We'll update the calculator as soon as the revised standard and methodology are confirmed. [Try WaterMonkey →](/tools/part-g-water-calculator/) If you've got a site where water is already the sticking point — or a planning condition asking for something tighter than 110 — [get in touch](/contact/) and we'll tell you how we'd sort it. *Sources: [Review of Water Efficiency Standards in the Building Regulations 2010 — Defra consultation](https://consult.defra.gov.uk/water-efficiency-demand/review-of-water-efficiency-standards) · [Water UK backs tougher water efficiency standards for new homes — Water Magazine, 3 August 2026](https://www.watermagazine.co.uk/2026/08/03/water-uk-backs-tougher-water-efficiency-standards-for-new-homes/) · [CIH briefing on Defra's Part G consultation](https://www.cih.org/news/cih-briefing-on-defra-s-consultation-on-updating-part-g-of-the-building-regulations-on-water-efficiency-in-new-homes/)* --- # Your window U-values are about to get harder (and more honest) URL: https://energycount.co.uk/news/window-doorset-u-values-adl-2026/ Date: 2026-07-06 Here's a change hiding in plain sight inside the Future Homes Standard: the way window and door **U-values** are calculated and declared is being overhauled. It's not the headline the trade press ran with, but it lands squarely on assessors' desks — because these are numbers you type straight into your SAP model. ## What's actually changing Today, a window U-value is typically calculated on a **standard reference size** — a fixed benchmark pane that rarely matches what's actually fitted. It's a tidy simplification, but it flatters the paperwork: a real window is seldom that exact size, so the declared figure and the installed reality drift apart. From **24 March 2027** in England (4 March 2027 in Wales), Approved Document L 2026 requires the declared U-value to reflect the **actual size and configuration** of every window and doorset installed — a far more rigorous, product-by-product approach calculated in line with **BR 443** and **EN ISO 10077-1/-2** ([Specification Online, 10 June 2026](https://specificationonline.co.uk/articles/2026-06-10/bsi/new-certification-launched-to-help-industry-comply-with-the-future-homes-standard)). ## Why the numbers go up This is the bit worth internalising: smaller windows generally have a **worse** U-value, not a better one. Frames conduct heat more readily than the glazed unit, so the more frame you have relative to glass — as in a small window — the higher the whole-window U-value climbs. In practice, a product currently declared at around **1.30 W/m²K** on a standard reference size can recalculate closer to **1.40–1.50 W/m²K** once the real dimensions and all the correct components are accounted for ([British Woodworking Federation](https://www.bwf.org.uk/latest-news/changes-to-u-values-explained/)). Nobody's product got worse overnight — the methodology just stopped rounding in the specifier's favour. ## What it means for assessors A useful line to hold: **you set the target, the supplier certifies the value.** As the assessor you can specify the U-value a dwelling needs — say, windows at 1.30 W/m²K to make the fabric energy balance work — but you can't calculate or certify the window's U-value on the manufacturer's behalf. That declared figure is the supplier's responsibility, produced with the correct Future Homes Standard methodology. For **SAP 10.3** — still the sole compliance route at Future Homes Standard launch — the practical upshot is simple: the U-value inputs you use must reflect each window's **as-designed** configuration, not a generic default or an optimistic reference-size figure. Ask suppliers for U-values calculated to the new method, and treat any old standard-size declaration with caution. To help the market get this right, BSI has just launched two new **Certificates of Conformity** for the underlying calculation data and software, and ran an introductory webinar on 1 July 2026 ([Specification Online](https://specificationonline.co.uk/articles/2026-06-10/bsi/new-certification-launched-to-help-industry-comply-with-the-future-homes-standard)). ## The bigger fabric picture Tighter fabric standards mean every element of the heat-loss calculation gets more scrutiny — glazing today, and the **junctions** around it just as much. As walls and openings improve, the heat escaping through poorly-detailed thermal bridges becomes a bigger share of the total, and leaning on the default junction Psi-value of 0.15 W/m·K carries a real penalty in your assessment. That's where **ΨMonkey** earns its keep — a browser-based Psi-value calculator that does proper **BS EN ISO 10211** thermal modelling to **BR 497** conventions, without the desktop-software faff or the consultancy invoice. Get your window U-values honest and your junction Psi-values calculated, and your SAP figures have a lot less to prove. [Try ΨMonkey →](/tools/psi-calculator/) *Sources: [New certification launched to help industry comply with the Future Homes Standard — Specification Online, 10 June 2026](https://specificationonline.co.uk/articles/2026-06-10/bsi/new-certification-launched-to-help-industry-comply-with-the-future-homes-standard) · [Changes to U-Values Explained — British Woodworking Federation](https://www.bwf.org.uk/latest-news/changes-to-u-values-explained/) · [Approved Document L Volume 1 2026 (gov.uk)](https://assets.publishing.service.gov.uk/media/69c122a6cfa346b9d4704a55/ADL1_2026.pdf)* --- # The Nature Restoration Fund just took its first legal step URL: https://energycount.co.uk/news/nature-restoration-fund-nutrient-regulations-laid/ Date: 2026-06-24 If you've had a housing scheme stuck in a protected catchment, this one matters. On **18 June 2026** the government laid the first two pieces of secondary legislation for the **Nature Restoration Fund (NRF)** before Parliament — the machinery that's meant to give developers a simpler way to deal with nutrient pollution than the site-by-site mitigation we've all been wrestling with ([Defra Environment blog, 19 June 2026](https://defraenvironment.blog.gov.uk/2026/06/19/laying-the-groundwork-for-the-nature-restoration-fund/)). ## What actually got laid Two sets of regulations, both now on the statute books in draft: - **The Nature Restoration Levy Regulations 2026** — the framework for how the nature restoration levy will work, i.e. the route by which developers will eventually be able to discharge certain environmental obligations with a payment. ([legislation.gov.uk](https://www.legislation.gov.uk/ukdsi/2026/9780348284379/contents)) - **The Environmental Delivery Plans (Appropriate Prioritisation) Regulations 2026** — how Natural England must prioritise different "conservation measures" when it writes an Environmental Delivery Plan, honouring the mitigation hierarchy commitment made during the Bill's passage. These regulations **came into force on 9 July 2026**. ([legislation.gov.uk](https://www.legislation.gov.uk/uksi/2026/655/contents/made)) Both flow from the **Planning and Infrastructure Act 2025**, which got Royal Assent in December 2025 and created the NRF in the first place. ## How the NRF is meant to work The idea is straightforward, even if the delivery is anything but. Rather than commissioning your own mitigation for every site, you'll be able to pay a **nature restoration levy** into a central fund. Natural England pools those payments and delivers nutrient mitigation at a landscape scale — wetlands, river restoration, that sort of thing — through area-specific **Environmental Delivery Plans (EDPs)**. Where an EDP is in place and covers your impact, the levy payment replaces the bespoke nutrient budgeting and credit-hunting that has held up tens of thousands of homes across affected catchments. ## The important caveat: nothing is live yet Here's the bit to be clear-eyed about. Laying regulations is a step *towards* the fund, not the switch being flicked. Natural England has said it will **shortly launch the formal consultation on the first draft EDP — which will deal with nutrient pollution** — and every draft EDP must go through a public consultation of at least 28 days. Only once the legislation is in place and consultations are complete will finalised EDPs go to the Secretary of State for approval before they "go live" for developers. So for now, **nutrient neutrality still applies exactly as it does today.** If your site sits in one of the affected catchments, you still need a nutrient budget and mitigation to get a planning consent — the NRF is the future route, not yet the present one. ## What this means for you Two practical takeaways. First, keep doing your nutrient calculations properly — the current regime is unchanged until an approved EDP actually covers your area, and a sound nutrient budget remains the foundation of any consent or mitigation deal. Second, watch for that first nutrient EDP consultation; when it lands it'll set out the proposed conservation measures *and* the levy charging schedule, which is the number every developer will want to compare against the cost of buying credits today. Either way, it starts with knowing your numbers. **NutrientMonkey** works out the nitrogen and phosphorus load for your scheme across England's affected catchments — in your browser, no sign-up — so whether you're mitigating the old way or sizing up the levy when it arrives, you're working from a defensible budget rather than a guess. [Try NutrientMonkey →](/tools/nutrient-neutrality-calculator/) *Sources: [Laying the groundwork for the Nature Restoration Fund — Defra Environment blog, 19 June 2026](https://defraenvironment.blog.gov.uk/2026/06/19/laying-the-groundwork-for-the-nature-restoration-fund/) · [The Nature Restoration Levy Regulations 2026 (legislation.gov.uk)](https://www.legislation.gov.uk/ukdsi/2026/9780348284379/contents) · [The Environmental Delivery Plans (Appropriate Prioritisation) Regulations 2026 (legislation.gov.uk)](https://www.legislation.gov.uk/uksi/2026/655/contents/made) · [Nature Restoration Fund Implementation Plan (gov.uk)](https://www.gov.uk/government/publications/nature-restoration-fund-implementation-plan)* --- # The Future Homes Standard is real — what ADL 2026 changes URL: https://energycount.co.uk/news/future-homes-standard-adl-2026/ Date: 2026-06-19 After years of "it's coming, honest," the Future Homes and Buildings Standards are no longer a rumour. On **24 March 2026**, MHCLG published the new statutory guidance — **Approved Document L 2026** (Volumes 1 and 2) plus an updated **Approved Document F** — alongside The Building Regulations etc. (Amendment) (England) Regulations 2026. ## The dates that matter The headline you need to diarise: the changes **come into force on 24 March 2027**. There's a one-year buffer too — for non-HRB work, projects with a building notice, initial notice or full-plans application submitted **before 24 March 2027** can still build to current standards, provided work starts **before 24 March 2028**. Higher-risk buildings get a slightly later switch-on of **24 September 2027** with their own transitional rules. In short: you've got runway, but the clock is now genuinely ticking. ([Building Circular 01/2026, gov.uk](https://www.gov.uk/government/publications/the-future-homes-and-buildings-standards-building-circular-012026/the-future-homes-and-buildings-standards-building-circular-012026-letter)) ## What's new in the rules The big-ticket changes amend the Building Regulations 2010 to bake in low-carbon heating and high-efficiency fabric, so new homes won't need retrofitting to hit zero-carbon-in-use as the grid decarbonises. Notable bits: - A **new functional requirement (L3)** mandating on-site renewable electricity generation (think solar PV) for new dwellings and buildings containing dwellings. - Part L of Schedule 1 reworded to cover **both** cutting greenhouse gas emissions **and** conserving energy. - "Fixed building services" widened to include lifts, escalators and moving footways in non-dwelling buildings. - A new **regulation 40C** requiring homeowner information (the Home User Guide) in a usable format. And — importantly for the carbon maths — the old 2013 and 2021 transitional arrangements that let people keep building to 2010 energy standards are being revoked. ## What about SAP and the Home Energy Model? One thing that trips people up: **at launch, SAP 10.3 is the only methodology** you can use to demonstrate compliance. The much-discussed Home Energy Model (HEM) isn't the approved tool on day one — it follows a minimum of three months after the standard goes live, with a confirmed dual-running period before it eventually replaces SAP. So for now, plan around SAP 10.3. ## What this means for you (and your junctions) Here's the bit competitors gloss over. Tighter fabric standards make **thermal bridging** matter *more*, not less. As walls, roofs and floors get better insulated, the heat that sneaks out through poorly-detailed junctions becomes a bigger slice of the total loss. Lean on the default junction Psi-value of 0.15 W/m·K and you'll be carrying a hefty, avoidable penalty in your calculation. The fix is the same as it's always been, just higher-stakes: calculate your junction Psi-values properly to **BS EN ISO 10211**, following **BR 497** conventions, rather than accepting worst-case defaults. Get the details right on paper and your SAP figures breathe a lot easier. That's exactly what **ΨMonkey** is for — a browser-based Psi-value calculator that does ISO 10211 thermal modelling without the stuffy desktop software or the eye-watering consultancy invoice. Model your junctions, drop the real numbers into your assessment, and give the Future Homes Standard the respect it deserves (while not taking the paperwork too seriously). [Try ΨMonkey →](/tools/psi-calculator/) *Sources: [Building Circular 01/2026 (gov.uk)](https://www.gov.uk/government/publications/the-future-homes-and-buildings-standards-building-circular-012026/the-future-homes-and-buildings-standards-building-circular-012026-letter) · [Approved Document L Volume 1 2026 (gov.uk)](https://assets.publishing.service.gov.uk/media/69c122a6cfa346b9d4704a55/ADL1_2026.pdf) · [The Building Regulations etc. (Amendment) (England) Regulations 2026 (legislation.gov.uk)](https://www.legislation.gov.uk/uksi/2026/335/made)* --- # The Home Energy Model just hit snooze (and that's fine) URL: https://energycount.co.uk/news/home-energy-model-launch-delayed/ Date: 2026-06-19 Quick one for anyone watching the Future Homes Standard like a hawk: on **8 June 2026** the government quietly pressed pause on the **Home Energy Model (HEM)** launch. HEM was widely expected to arrive around now — the Future Homes Standard documents had flagged it would be approved "no earlier than three months after publication," which pointed to a June 2026 window. Instead, it's being held back for final internal assurance, and is now expected "in the coming months" rather than on any fixed date ([HEM Guide timeline, verified against GOV.UK](https://home-energy-model.co.uk/timeline/)). So, no panic. Nothing has gone backwards. ## What this actually changes Practically? Very little changes *today* — and that's the point. **SAP 10.3 remains the sole approved methodology for Future Homes Standard compliance.** It was always going to be the only route at the FHS launch on **24 March 2027**, with HEM following at least three months later and then running alongside SAP 10.3 for a minimum of 24 months. This delay just nudges the start of that dual-running period a little further out. In other words: the methodology you'll be using for FHS submissions on day one hasn't changed. SAP 10.3 — updated with the new FHS notional dwelling specs and forward-looking carbon factors — is still the tool of the moment, and now for a touch longer than some had pencilled in. ## Why a delay is genuinely good news We'd rather have a robust calculation engine than a rushed one. HEM is a big leap — half-hourly modelling (17,520 timesteps versus SAP's monthly 12), centralised calculation through the **ECaaS** cloud platform, and a serious step up in the volume of input data it expects. Getting that right before it becomes a compliance route matters far more than hitting an arbitrary launch month. A delay for "final assurance" is the regulator doing the sensible thing. ## What this means for you If you're an assessor or developer, here's the chilled-out version: Keep building your SAP 10.3 confidence — it's the route that counts at launch and for a good while after. Don't down tools on HEM prep, though: when it arrives, HEM will *punish* missing data with deliberately punitive defaults, so the teams who start collecting detailed product, geometry and junction data now will be the ones gliding through later. And one detail that's easy to miss in all the heat-pump-and-solar headlines: **thermal bridging still matters under both routes.** Whether you're in SAP 10.3 today or HEM tomorrow, junction psi-values feed straight into your fabric performance — and HEM expects a psi-value for *each* junction or an accredited construction detail reference. Sloppy thermal bridging is one of the quietest ways to fail your fabric energy efficiency target. ## Sort your psi-values the easy way That's exactly what **ΨMonkey** is for. It calculates thermal bridging psi-values to BS EN ISO 10211 in your browser — no clunky desktop software, no PhD required — so your junctions are nailed down whichever compliance route you end up taking. Give it a spin and take one variable off your plate while everyone else waits for HEM to wake up. [Try ΨMonkey →](/tools/psi-calculator/) *Sources: [Home Energy Model timeline & status (HEM Guide)](https://home-energy-model.co.uk/timeline/) · [FHS compliance pathways](https://home-energy-model.co.uk/future-homes-standard/compliance/) · [GOV.UK — Home Energy Model consultation](https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-standard-assessment-procedure-sap)*