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01Building regulations

How much do SAP calculations cost in London?

SAP calculations for a London home cost from £245 with us, as a fixed fee with no VAT to add. We run the calculation on your drawings and specification through an assessor we coordinate, and re-run it as the design changes until the plans are approved.

From £245

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    What the calculation costs and does

    SAP, the Standard Assessment Procedure, is the model used to show a home meets the energy rules. Our calculations, from £245, are run by an assessor we coordinate, using your drawings and specification. You get the submission documents building control expects with the full plans.

    If the first run fails, you do not get just a red mark. You get a list of what to change, starting with the least expensive fix: a different glazing spec or a thicker layer of roof insulation before a redesign.

    What you receiveThe calculation on your drawings; A ranked list of fixes if it fails; Documents for the full plans application; Re-runs as the design changes; An EPC on completion, for a new dwellingiThe calculation on your drawingsiiA ranked list of fixes if it failsiiiDocuments for the full plans applicationivRe-runs as the design changesvAn EPC on completion, for a new dwelling
    Re-runs are included until the plans are approved.

    When you need one at all

    For an extension to an existing home, Approved Document L gives you choices. You can meet the limiting U-values: 0.15 W/m²K for a new roof, 0.18 for a wall or floor, 1.4 for windows and doors. The alternatives are an area-weighted U-value check or a SAP calculation against a notional extension.

    A SAP route is usually chosen when the simple limits cannot all be met, for example by a design with a large rooflight, or when insulation depth is restricted. A new dwelling needs SAP, or under the 2026 edition the Home Energy Model.

    A slate roof pitch with a rooflight set into it, seen from the roof of a house being renovated
    A rooflight in a slate roof: roof glazing counts towards the glazing limit and has its own U-value to meet.Photograph: Gareth1953 All Right Now, CC BY 2.0

    Glass is where extensions fail

    The simple route also limits glazing: windows, roof windows, rooflights and doors in an extension should not exceed 25 per cent of the extension's floor area, plus the area of any openings removed. A glazed rear wall and a rooflight can pass that quickly.

    That is when the calculation earns its cost. A SAP run lets us trade glazing against better insulation, rather than cut the glass.

    What is changing in 2027

    The 2026 edition of Approved Document L takes effect on 24 March 2027 for work that is not higher-risk. The 2021 documents continue where plans are deposited before that date and work starts before 24 March 2028, under the government's transitional circular.

    For new homes the 2026 edition names two methods, the Home Energy Model and SAP. We use whichever applies on your dates. Our SAP calculations page is kept up to date as the rules move.

    A row of colour-washed Victorian terrace houses on Falkland Road in Kentish Town under a blue sky
    A Victorian terrace: when an old house is altered, the new elements are measured against the limits, not the old walls.Photograph: Images George Rex, CC BY-SA 2.0

    Ordering

    Send your drawings and the specification, even if rough. We tell you whether the simple route will pass and whether a SAP calculation is needed.

    From drawings to a passSend drawings and specification; Fixed fee in writing; Calculation run; Fixes listed if it fails; Issued with the full plansi

    Send drawings and specification

    ii

    Fixed fee in writing

    iii

    Calculation run

    iv

    Fixes listed if it fails

    v

    Issued with the full plans

    We start with the least costly change.

    The figures, with sources

    1. 0.15 / 0.18

      Limiting U-values, W/m²K, for a new roof and for a new wall or floor in an existing home.

      Source: Approved Document L Volume 1, Table 4.2, checked 15 Oct 2026

    2. 1.4

      Limiting U-value, W/m²K, for new windows and doors, or a window energy rating of Band B.

      Source: Approved Document L Volume 1, Table 4.2, checked 15 Oct 2026

    3. 25%

      Most glazing an extension should have as a share of its floor area, plus openings removed.

      Source: Approved Document L Volume 1, paragraph 10.7, checked 15 Oct 2026

    4. SAP route

      An area-weighted U-value check or a SAP calculation against a notional extension can replace the simple limits.

      Source: Approved Document L Volume 1, paragraphs 10.9 and 10.10, checked 15 Oct 2026

    5. 24 Mar 2027

      Day the 2026 edition of Approved Document L starts to apply, for ordinary non-higher-risk building work.

      Source: Approved Document L Volume 1, 2026 edition, checked 15 Oct 2026

    6. HEM and SAP

      Methods the 2026 edition names for new dwellings: the Home Energy Model and SAP.

      Source: Approved Document L Volume 1, 2026 edition, checked 15 Oct 2026

    7. Transition

      Where plans go in before 24 March 2027 and work begins before 24 March 2028, the 2021 documents still apply.

      Source: Circular 01/2026, transitional arrangements, checked 15 Oct 2026

    Questions

    Does every extension need a SAP calculation?

    No. Many pass on the simple limits. We tell you which route fits and the cost of each.

    Who runs the calculation?

    An assessor we coordinate, working from your drawings and specification. You deal with us.

    What if it fails?

    You get a list of changes, starting with the least costly, and we re-run it until it passes.

    Do I need an EPC afterwards?

    For a new dwelling, one is needed on completion. We arrange it where it applies.

    The fee for sap calculations (part l)

    SAP calculations (Part L)

    from £245

    The total you pay. No VAT to add.

    Get a fixed quote from £245

    What you get

    • The calculation run on your drawings and specification
    • A list of fixes, starting with the least costly
    • Submission documents for building control
    • Re-runs while the design changes
    • An EPC for a new dwelling, where needed
    House extension under construction with scaffolding, new glazed doors and building materials

    0.15 / 0.18

    Limiting U-values, W/m²K, for a new roof and for a new wall or floor in an existing home. Source: gov.uk

    Photograph: Brett Jordan

    02Guides

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    SAP Calculations Cost in London: From £245