Last reviewed against the sources on . England unless stated; Wales and Scotland differ where noted. The same figures are in our plain-text feed for AI assistants, llms-full.txt.
Part L U-values (W/m²K)
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 differs only in how the notional heat pump is modelled — see the Future Homes Standard guide. Explained: U-values · Calculate: U-Monkey (free) · Extensions: the 25% glazing checker.
Part L editions and transitional dates
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. Not sure which edition your scheme falls under? Run the Part L edition checker. Explained: Part L · Future Homes Standard.
SAP: the carbon and primary energy factors, and the notional dwelling
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 in Part L, DER and TER and TFEE and DFEE. SAP 10 changes: what's new.
Junction Ψ-values (W/m·K) — calculated, not default
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. Every cell opens the app with that junction and wall loaded, so the number is reproducible.
Ψ in W/(m·K), with fRsi beneath. Red is fRsi below 0.75, the BRE IP 1/06 condensation criterion for dwellings. Marked negatives on a non-inverted junction mean the template's default detail doesn't suit that wall — a prompt to model your own, not a figure to use. Click any figure to open that junction and wall in ΨMonkey with Ψ live.
The eight walls, and how these figures were produced
- Cavity masonry — full fill (accredited default)U 0.176 W/m²K100 mm Facing brick · 100 mm PIR insulation (foil-faced) · 100 mm Aerated concrete block (general) · 20 mm Plasterboard on dabs (12.5 + 15mm)
- Cavity masonry — partial fill + 50 mm clear cavityU 0.278 W/m²K100 mm Facing brick · 50 mm Air cavity (ISO 6946, ≥25mm) · 50 mm PIR insulation (foil-faced) · 100 mm Aerated concrete block (general) · 20 mm Plasterboard on dabs (12.5 + 15mm)
- Timber frame — brick clad, 140 mm studs (15% bridged)U 0.271 W/m²K100 mm Facing brick · 50 mm Air cavity (ISO 6946, ≥25mm) · 20 mm OSB/3 (18mm) · 140 mm Mineral wool (glass/rock) + 15% Structural timber · 20 mm Plasterboard on dabs (12.5 + 15mm)
- Timber frame — brick clad, 140 studs + service voidU 0.258 W/m²K100 mm Facing brick · 50 mm Air cavity (ISO 6946, ≥25mm) · 20 mm OSB/3 (18mm) · 140 mm Mineral wool (glass/rock) + 15% Structural timber · 25 mm Air cavity (ISO 6946, ≥25mm) + 9% Structural timber · 20 mm Plasterboard on dabs (12.5 + 15mm)
- Timber frame — 140 studs + 50 mm PIR over the sheathingU 0.163 W/m²K100 mm Facing brick · 50 mm Air cavity (ISO 6946, ≥25mm) · 50 mm PIR insulation (foil-faced) · 20 mm OSB/3 (18mm) · 140 mm Mineral wool (glass/rock) + 15% Structural timber · 25 mm Air cavity (ISO 6946, ≥25mm) + 9% Structural timber · 20 mm Plasterboard on dabs (12.5 + 15mm)
- Timber frame — render / rainscreen, 140 mm studsU 0.278 W/m²K20 mm External silicone render · 50 mm Air cavity (ISO 6946, ≥25mm) · 20 mm OSB/3 (18mm) · 140 mm Mineral wool (glass/rock) + 15% Structural timber · 20 mm Plasterboard on dabs (12.5 + 15mm)
- Closed panel / twin stud — 300 mm cellulose (8% bridged)U 0.112 W/m²K20 mm External silicone render · 50 mm Air cavity (ISO 6946, ≥25mm) · 60 mm Woodfibre board (Steico) · 300 mm Cellulose fibre (blown) + 8% Structural timber · 20 mm OSB/3 (18mm) · 20 mm Plasterboard on dabs (12.5 + 15mm)
- CLT + external insulation — 100 CLT, 160 woodfibreU 0.179 W/m²K20 mm External silicone render · 160 mm Woodfibre board (Steico) · 100 mm Cross-laminated timber (CLT) · 25 mm Air cavity (ISO 6946, ≥25mm) + 9% Structural timber · 20 mm Plasterboard on dabs (12.5 + 15mm)
Each figure is ΨMonkey's own result for its standard template of that junction, with the external wall set to the named build-up and every other element — floors, roofs, party walls, lintels, windows — at the template's shipped default. Boundary conditions to BS EN ISO 10211, Ti 20 °C / Te 0 °C, convergence 10⁻⁶. Solved 2 September 2026 on the app as shipped; regenerated whenever the app changes. How the solver itself is checked is on the validation page.
All 38 templates: the full Ψ-value library. Explained: thermal bridging · ACDs and Recognised Construction Details · Calculate your own: ΨMonkey (free; Building Control PDF £35 +VAT).
Air tightness (Part L)
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: air tightness testing, with the pre-test checklist.
Part O overheating — the simplified method tables
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: Part O · Service: Part O assessments · TM59:2026 — what changed.
Part G water efficiency
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. Why London's 105-excluding-external is the same target as 110: explained. Machine-readable: CSV and JSON. Calculate: WaterMonkey (free; Building Control PDF £25 +VAT). Explained: the Part G calculation · 125 vs 110.
Part E sound insulation
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. Pre-completion testing is the default route; registered Robust Details are the alternative for new-build houses and flats. Service: sound testing.
Soakaways — BRE Digest 365 in numbers
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 explained. Calculate: SoakMonkey (free; Building Control PDF £25 +VAT) · the BRE 365 method.
Nutrient neutrality — the 27 Natural England catchments
Natural England's nutrient neutrality advice and catchment calculators (NECR459 methodology, 20% precautionary buffer). N = nitrogen, P = phosphorus. Checked 4 September 2026.
| Catchment | Designated site | Nutrient | Region |
|---|---|---|---|
| Poole Harbour | Poole Harbour SPA / Ramsar | Nitrogen | Dorset |
| Solent | Solent (incl. Chichester & Portsmouth Harbours) | Nitrogen | Hampshire, West Sussex & Isle of Wight |
| Tees (Teesmouth) | Teesmouth & Cleveland Coast SPA / Ramsar | Nitrogen | Teesside, Durham & North Yorkshire |
| Lindisfarne | Lindisfarne SPA / Ramsar | Nitrogen | Northumberland |
| Stodmarsh | Stodmarsh SAC / SPA / Ramsar | N and P | Kent |
| The Broads | The Broads SAC | N and P | Norfolk & Suffolk |
| River Wensum | River Wensum SAC | N and P | Norfolk |
| Chesil & the Fleet | Chesil & the Fleet SAC / SPA / Ramsar | N and P | Dorset |
| Hornsea Mere | Hornsea Mere SPA | N and P | East Yorkshire |
| Oak Mere | Oak Mere SAC | N and P | Cheshire |
| Rostherne Mere | Rostherne Mere Ramsar | N and P | Cheshire |
| West Midlands Mosses | West Midlands Mosses SAC | N and P | Shropshire, Staffordshire & Cheshire |
| River Clun | River Clun SAC | N and P | Shropshire |
| River Avon (Christchurch) | River Avon SAC (→ Christchurch Harbour) | Phosphorus | Wiltshire, Hampshire & Dorset |
| Somerset Levels & Moors | Somerset Levels & Moors SPA / Ramsar | Phosphorus | Somerset |
| River Itchen | River Itchen SAC | Phosphorus | Hampshire |
| River Axe | River Axe SAC | Phosphorus | Somerset, Devon & Dorset |
| River Camel | River Camel SAC | Phosphorus | Cornwall |
| Derwent & Bassenthwaite | River Derwent & Bassenthwaite Lake SAC | Phosphorus | Cumbria |
| River Eden | River Eden SAC | Phosphorus | Cumbria |
| River Kent | River Kent SAC | Phosphorus | Cumbria |
| River Lambourn | River Lambourn SAC | Phosphorus | Berkshire |
| River Lugg | River Lugg SAC (River Wye system) | Phosphorus | Herefordshire |
| River Mease | River Mease SAC | Phosphorus | Leicestershire, Derbyshire & Staffordshire |
| Esthwaite Water | Esthwaite Water Ramsar | Phosphorus | Cumbria |
| Peak District Dales | Peak District Dales SAC | Phosphorus | Derbyshire & Staffordshire |
| Roman Walls Loughs | Roman Walls Loughs SAC | Phosphorus | Northumberland |
Each catchment page carries the credit position where one is known. Calculate a budget: NutrientMonkey (free; planning-ready PDF £79 +VAT). Machine-readable list: CSV and JSON. Policy: the Nature Restoration Fund.
Regs calendar
Dates from the instruments, circulars and consultations linked in each row, as covered in our regs watch. Checked 4 September 2026.
Updates land in the news section and the RSS feed as they happen.
Citing this page
Energycount, Building regulations reference, energycount.co.uk/reference/, reviewed 4 September 2026. Every table names the document and table it is taken from; where a figure has changed between editions, both are given. If you find a figure that has moved, tell us and we will correct it and date the correction.