How Much Do SAP Calculations Cost?
SAP calculations: From £95 + VAT. Guide price. Get a free quote for your project. This guide explains which calculation you need, what to send us and how to avoid paying for changes later.
In this guide
Which SAP calculation do I need?
New houses and flats
A new build SAP (L1A). You need a design-stage SAP before work starts and an as-built SAP at the end.
Conversions
A conversion SAP (L1B) where a building is being changed into homes and the route you are using needs one.
Extensions
Usually none. You only need one if the glazing is over the limit and you choose that route.
Why you pay for two stages on a new build
A new home goes through SAP twice, because the first version is a prediction and the second is the finished building.
Design stage
The drawings and specification are modelled before work starts, to show the home can meet the targets.
As-built
The model is updated at the end with what was really built and the air test result. This produces the Energy Performance Certificate.
Ask us to quote for both together, so you can see the full cost from the start.
What can add to the cost?
The bigger costs usually come from the build, not the calculation. Watch out for these:
- Leaving it late. If the SAP is done after the walls are up, fixing a fail can mean changing insulation, glazing or heating that is already on site.
- Changing the design. Different windows, heating or insulation mean the model has to be updated. Tell us before you make a change, not after.
- Missing information. Without clear details, an assessor has to use cautious assumptions, which can make it harder to pass.
- A failed air test. The as-built SAP needs the measured result, so a fail can hold up your EPC and sign-off.
What to send for a quote
- Floor plans, elevations and sections.
- The site address and the type of project.
- What the walls, floors and roof will be built from, or the U-values if your designer has them.
- The window and door specification.
- The planned heating, hot water, ventilation and any renewables, such as solar panels.
If you do not have all of this yet, send what you have. It can also be efficient to ask for overheating and Water Calculations at the same time, because they use the same drawings.
Is anything changing in 2027?
Yes. A new Approved Document L takes effect on 24 March 2027, or 24 September 2027 for higher-risk building work. Transitional arrangements apply, so ask your Building Control body which edition covers your project. See our Future Homes Standard 2027 guide.
Frequently asked questions
How much do SAP calculations cost?
SAP calculations are From £95 + VAT. Guide price. Get a free quote for your project.
Do I need a SAP calculation for an extension?
Usually not. Most extensions just need to meet the U-values in Approved Document L.
What is the difference between SAP and an EPC?
SAP is the calculation. The Energy Performance Certificate is the rating produced from it when a new home is finished.
Does a new house need two SAP calculations?
Yes. A design-stage SAP before work starts and an as-built SAP at the end, using the air test result.
What is included in the price?
Your quote will set out exactly what is included for your project, so you can compare it properly.
Who needs to see the SAP calculation?
Your Building Control body, council or private. We can arrange that too: see Private Building Control.
Get a Free Quote for Your Project
Send us your drawings and specification and we will confirm which calculation applies.
Last reviewed: November 2026. General guidance for England only. Get project-specific advice before relying on it.