What is SAP?

The Standard Assessment Procedure - how the UK calculates a new home's energy performance

SAP stands for Standard Assessment Procedure. It's the UK Government's official method for calculating the energy performance of dwellings. It turns a building's design and construction into a single energy efficiency score, which then feeds into Part L sign-off and the Energy Performance Certificate (EPC) you see when a home is sold or rented.

If you've ever seen a home advertised with an EPC rating of "C" or "B," that letter came out of a SAP calculation.

What SAP calculates

SAP models the expected energy use of a dwelling. It looks at:

  • Fabric - walls, floors, roof, windows, doors, and thermal bridging
  • Heating and hot water - system type, efficiency, controls
  • Ventilation - natural, mechanical, or heat-recovery
  • Lighting - proportion of low-energy fittings
  • Renewables - solar PV, solar thermal, heat pumps, wind
  • Airtightness - based on a pressure test result

All of that goes into a calculation that produces the SAP score (1 to 100+) and the EPC band (A to G). Higher is better.

The two stages of SAP

For a new build, SAP happens twice:

  1. Design-stage SAP. Before construction starts, an OCDEA runs the calculation on the design to show it should meet Part L. This is what you submit to Building Control as part of your Part L application.
  2. As-built SAP. Once the dwelling is finished, the OCDEA runs the calculation again using what was actually installed. Any change from the design - say, a different boiler model, or less insulation than specified - has to be reflected here.

The as-built SAP is what ultimately feeds the final EPC. The Appendix B photographic evidence from site is what backs up the as-built SAP - proof that what's in the calculation matches what's on the plot.

Buildsnpper organises the site-side of as-built SAP: photos mapped to each Appendix B section, GPS and timestamps automatic, reports straight to your OCDEA. From £6.67 per month, 14-day free trial. See how it works.

Who actually runs SAP

An accredited OCDEA (On Construction Domestic Energy Assessor) runs SAP for new builds. They're registered with one of the UK accreditation bodies - Elmhurst Energy, Stroma Certification, Sava, Quidos, or ECMK - and they have to keep up with methodology updates as SAP versions change.

For existing homes, an ordinary DEA produces the EPC using a simpler version of SAP (called RdSAP). They don't need the full OCDEA qualification because they're working from what's already there, not signing off new-build compliance.

SAP versions and the Future Homes Standard

SAP isn't fixed. The methodology is updated periodically - SAP 10.2 has been the common version through the 2025 transition, with further updates landing as the Future Homes Standard is implemented. Each version tightens the defaults and raises the bar for what counts as a compliant design.

Builders don't run SAP themselves, but it's worth knowing which version your assessor is using - it affects what specifications will pass and which heating technologies are penalised or rewarded.

How SAP connects to Part L

Part L sets the rules. SAP measures whether the building meets them. Appendix B provides the site evidence. The OCDEA ties all three together in a BREL report that Building Control signs off before handover.

Frequently asked questions

What is SAP in UK Building Regulations?

SAP is the Standard Assessment Procedure, the UK Government's method for calculating the energy performance of dwellings. It produces the energy efficiency score used for Part L compliance and the EPC rating.

Who runs a SAP assessment?

An accredited OCDEA (On Construction Domestic Energy Assessor) runs SAP for new builds. A DEA runs RdSAP for existing dwellings. Both are registered with one of the UK accreditation bodies.

What's the difference between SAP and RdSAP?

SAP is used for new-build dwellings, based on the design and as-built construction. RdSAP (Reduced Data SAP) is a simplified version used for existing homes, where the assessor records what's already there rather than designing to a target.

What does SAP calculate?

SAP calculates a dwelling's energy performance based on fabric insulation, heating and hot water systems, ventilation, lighting, renewables, and airtightness. The output is an energy efficiency score (1-100+) and an EPC band (A-G).

When do I need a SAP assessment?

For a new-build dwelling, you need a design-stage SAP before starting construction, and an as-built SAP once the building is finished. The as-built SAP feeds the final EPC and the BREL report that signs off Part L compliance.

What's the difference between SAP and SBEM?

SAP is for dwellings. SBEM (Simplified Building Energy Model) is for non-dwellings like offices, shops, and industrial buildings. Both are UK methodologies used for Part L compliance, but they apply to different building types.

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