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 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). 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); and increasingly mortgage/valuation and net-zero policies on new homes. Our SAP calculations service covers all of them — and the New Build Compliance Pack bundles SAP with the water, acoustics and air-tightness 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 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 lowest storey area ÷ 6.5 (for flats, ÷ 6.5 × number of storeys). 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 or a heat pump. 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 to 0.233 kgCO₂/kWh — barely above mains gas (0.210), reflecting the greener grid. All-electric designs, brutal to pass under SAP 2012, now have far more flexibility. It’s why heat pumps, 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 produces. More on 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.
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, the energy hierarchy and 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 can model your options.
Where it’s going: the Future Homes Standard
SAP 10 is the stepping stone to the Future Homes Standard — and that’s no longer a distant “someday.” Approved Document L 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 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 and PHPP 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 kgCO₂/kWh |
| 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
- SAP 10 carbon factors: electricity 0.233, gas 0.210 kgCO₂/kWh.
- 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 and Approved Document L.