SAP CalculationsFrom £225
How much do SAP calculations cost in London?
SAP calculations for a new London home, or a conversion that creates one, cost our fixed £225, with no VAT charged. An energy assessor we coordinate runs them from your drawings and specification, once at design stage and again when the work is complete, because building control wants evidence at both points.
The short answer: one fixed fee, two calculations
Our SAP fee is £225. For that you get a design-stage calculation for the building control application, a check of your walls, glazing, heating and ventilation against the standard, and a list of the specifications the building must be built to. If the first run fails, we advise what to change.
An as-built calculation follows when the work is complete, using the details the builder actually fitted, along with the documents building control and your Energy Performance Certificate need. The assessor is a specialist we coordinate, not someone in our own office.
- Design stage
The calculation is run from your drawings and specification, before work starts, for the building control application.
- Fix what fails
If the design misses the standard, we advise what to change in the fabric, glazing or heating.
- Build to the list
The builder follows the specifications the calculation relies on.
- As built
A second calculation records what was actually fitted, for completion and your EPC.
What SAP is for
The government describes the Standard Assessment Procedure as having two main uses: to demonstrate compliance of new homes with Part L of the Building Regulations and to generate Energy Performance Certificates for all homes. SAP 10.3 is currently the sole approved methodology, according to the page's update of 8 June 2026, and the Home Energy Model will replace SAP for the energy rating of dwellings.
That replacement is why the date matters. The Future Homes and Buildings Standards regulations come into force on 24 March 2027, with transitional arrangements for building notices and full-plans applications given before that date, where the work is commenced before 24 March 2028 (MHCLG circular). A new-build project that is going to be submitted around then needs us to check which version of the rules applies.
Who needs one, and who does not
Approved Document L Volume 1 says a new dwelling must be built to a minimum standard of total energy performance, evaluated by comparing the actual dwelling with a notional one, and that this must be carried out both at the design stage and when work is complete. That is the case for a new house, a new flat or a conversion that creates a dwelling.
An extension to an existing house is different. The same document asks that the total area of windows, roof windows, rooflights and doors in an extension should not exceed the sum of 25% of the floor area of the extension and the area of any openings that no longer exist. A simple extension that meets the elements and that limit may never need a SAP calculation, and we tell you so rather than sell you one.
The five days after completion
The regulations require the person carrying out the work to give the local authority a notice not later than five days after the work has been completed, as set out in the Approved Document. The as-built SAP records what was fitted, and your Energy Performance Certificate draws on it.
That is why a builder who skips the specified insulation or swaps the heating late is a problem for the calculation as well as for the home: the as-built run records what was fitted, and a change from the design stage can make a pass into a fail. We tell your builder what the calculation relies on before work starts.
Where it sits in the budget
A new-build project carries SAP alongside its planning and building regulations costs. Our post on new build drawings shows the whole picture, and the building regulations drawings post explains the set the calculation sits behind.
Our SAP calculations page shows the service. If you only need to know whether your extension needs one, ask before you buy.
Sources
Every figure in this article, where it comes from and a link to the original.
- to demonstrate compliance of new homes with Part L of the Building Regulations: GOV.UK Standard Assessment Procedure: the methodology has 2 main uses (source wording: "to demonstrate compliance of new homes with Part L of the Building Regulations"). www.gov.uk
- SAP 10.3 is currently the sole approved methodology: GOV.UK Standard Assessment Procedure (update 8 June 2026): (source wording: "SAP 10.3 is currently available as the sole approved methodology"). www.gov.uk
- the Home Energy Model will replace SAP for the energy rating of dwellings: GOV.UK Standard Assessment Procedure: (source wording: "The Home Energy Model will replace the SAP for the energy rating of dwellings"). www.gov.uk
- this must be carried out both at the design stage and when work is complete: Approved Document L Volume 1 (2021 edition incorporating 2023 amendments) para 1.1: (source wording: "This must be carried out both at the design stage and when work is complete"). assets.publishing.service.gov.uk
- 25% of the floor area of the extension: Approved Document L Volume 1 para 10.7(d)(i): the total area of windows, roof windows, rooflights and doors in extensions should not exceed the sum of (source wording: "25% of the floor area of the extension"). assets.publishing.service.gov.uk
- not later than five days after the work has been completed: Building Regulations 2010 as reproduced in Approved Document L Volume 1: (source wording: "Not later than five days after the work has been completed, the person carrying out the work shall give the local authority a notice"). assets.publishing.service.gov.uk
- 24 March 2027: MHCLG Building Circular letter 01/2026, 24 March 2026: (source wording: "The Regulations come into force on 24 March 2027"). www.gov.uk
Questions people ask
Is the energy assessor your own staff?
Do I pay VAT on your fee?
Does my loft conversion need SAP?
Does the Home Energy Model change what you do?
Do I get an EPC from it?
Photographs: Matt Bird (Unsplash License); John Cameron (Unsplash License).
SAP Calculations: a fixed fee from £225
Read more on the sap calculations service page, or send your address below and we reply within one working day.
SAP Calculations
from £225
Every price is the full fixed fee you pay. No VAT is charged. Council application fees are paid to the council separately.
What you get
- A design-stage SAP calculation for the building control application
- Checks of your fabric, glazing, heating and ventilation against the notional dwelling
- A list of the specifications the building must be built to
- Advice on what to change if the first run fails
- An as-built SAP once work is complete, with the details the builder actually fitted