What SAP is
The Standard Assessment Procedure is the government’s method for the energy rating of dwellings. It was first cited in the Building Regulations in 1994 and is the method behind Energy Performance Certificates.
Our fee is £225. An accredited assessor builds the model from your drawings, so the walls, roof, glazing and heating on the drawings are the ones that are scored.
Do an extension and a loft need one?
Usually the extension route is simpler. Approved Document L says the total area of windows, roof windows, rooflights and doors in an extension should not exceed 25% of its floor area, plus the area of any openings that no longer exist.
If a new window is created or enlarged in an existing home, the area of openings should not exceed 25% of the dwelling’s floor area, otherwise compensating measures should improve the energy efficiency. New windows must meet the standards in the document’s Table 4.2.
When a full calculation is needed
A new dwelling, including a house split into flats, is assessed as a whole. The calculation sets the fabric, heating and ventilation to meet the building regulations target, and we use it to settle choices such as glazing and insulation before the building control application.
Where we cannot be certain which route your project takes, we say so at the start rather than after you have paid.
By the numbers
1994
The year SAP was first cited in the Building Regulations as the method for assessing energy performance of dwellings.
Source: Standard Assessment Procedure (SAP) overview (GOV.UK)
25%
Largest share of an extension’s floor area that windows, roof windows, rooflights and doors may cover.
25%
The same limit against the whole dwelling when a new window is created or enlarged, unless compensating measures are taken.
Table 4.2
The fabric standards new windows, rooflights and doors must meet.
EPCs
Energy Performance Certificates use the SAP methodology.
Source: Standard Assessment Procedure (SAP) overview (GOV.UK)
SAP calculation costs: common questions
Is the assessor’s work in your price?
Yes. The fee is for the calculation through an accredited assessor, and the result goes with your building regulations application.
Will I get an energy certificate from this?
The calculation uses the same method as an EPC, but a certificate is a separate document. We tell you what your project needs.
Source: Standard Assessment Procedure (SAP) overview (GOV.UK)
Which version of SAP is used?
The assessor uses the version that applies to your application date. GOV.UK notes SAP has been updated several times and most recently in 2026.
Source: Standard Assessment Procedure (SAP) overview (GOV.UK)
Sources
- Standard Assessment Procedure (SAP) overview (GOV.UK)
- Approved Document L, volume 1: dwellings, 2021 edition incorporating 2023 amendments, section 10 (GOV.UK)
About the author. Ben Shaukat is Managing Director of Property Architecture Ltd, which trades as Planning Drawings.
Published by Planning Drawings. Checked against the sources above on . Planning rules change; check your council before you build.