Every new building, and many conversions and extensions, has to show it meets the energy efficiency rules in Part L of the Building Regulations. Which calculation you need depends on what the building is: SAP for homes, SBEM for non-domestic buildings.
SAP: dwellings
The Standard Assessment Procedure (SAP) calculates the energy use and carbon emissions of a home. It covers new houses and flats, and conversions that create new dwellings. You’ll still hear the older labels:
- L1A: new-build dwellings.
- L1B: work to existing dwellings, including conversions, change of use and some extensions.
A new home needs a design-stage SAP before work starts and an as-built SAP at the end, using the air tightness test result. The as-built SAP produces the Energy Performance Certificate (EPC).
SBEM: everything else
The Simplified Building Energy Model (SBEM) does the same job for non-domestic buildings such as offices, shops, warehouses, schools and commercial units. Again the older labels are still used:
- L2A: new non-domestic buildings.
- L2B: work to existing non-domestic buildings, such as extensions, refurbishments, fit-outs and change of use.
SBEM produces a BRUKL compliance report for Building Control and the commercial EPC on completion.
Send your drawings and specification. We’ll confirm which calculation applies and quote for design-stage and as-built work together.
Mixed-use buildings
A building with flats over shops needs both: SAP for each flat and SBEM for the commercial units. Common parts are usually assessed with the non-domestic part.
Do it early
Running SAP or SBEM at design stage shows whether your fabric, glazing, heating and renewables will pass before they’re fixed. Leaving it until the end risks expensive changes. The same drawings also feed overheating and water efficiency calculations, so it’s efficient to commission them together. Changes coming in with the Future Homes Standard make early modelling even more important.
Related services: L1A SAP, L1B SAP, L2A SBEM, L2B SBEM, EPCs.
Frequently asked questions
What is the difference between SAP and SBEM?
SAP is the energy calculation for dwellings (houses and flats). SBEM is for non-domestic buildings such as offices, shops and warehouses. Both show compliance with Part L and produce an EPC.
When do I need a SAP calculation?
For every new dwelling, at design stage before work starts and again as-built on completion. Conversions that create new dwellings also need one.
Do extensions need SAP or SBEM?
Many domestic extensions can comply without SAP by meeting the standard U-values. Large glazed extensions, or ones that don’t meet the standard specification, may need a calculation. Non-domestic extensions often need SBEM.
What does an as-built SAP need?
The final specification, any changes made on site, and the air tightness test result. It’s used to produce the EPC.
Last reviewed: October 2026. General guidance for England only. Rules change and every site is different, so get project-specific advice before relying on it.
More guides in the Developer Knowledge Centre · Services: L1A New Build SAP Calculations, L1B Conversion SAP Calculations, L2A SBEM Calculations, L2B SBEM Calcuations, Energy Performance Certificates