SAP and Part L energy calculations, £225 fixed
A new home, a flat conversion or a big extension needs a calculation showing it meets the energy rules. We arrange it through an accredited assessor, feed them the drawings and specification, and put the result into your building regulations set: £225.
- £225 fixed, arranged for you
- Accredited assessor used
- Result built into your drawings
What do SAP and Part L calculations cost?
The fee is £225, with no survey fee and no VAT to add. We coordinate the calculation: we brief an accredited assessor, give them the drawings and the proposed build-up, and return the result with the changes it needs. The assessor’s work and the certificate are what building control asks for.
What the £225 covers
- A check of which calculation your project needs: new dwelling, conversion or extension
- The brief to an accredited assessor, with the plans, the glazing, the heating and the insulation build-up
- The SAP calculation result and the report building control asks for
- Changes to the drawings and specification if the first result does not pass
- The result written into your building regulations drawings, so builder and inspector see the same figures
When do I need a SAP calculation?
For a new dwelling, and for a conversion that creates a dwelling. The Regulations require the energy performance to be calculated by an approved method and compared with a target, and for current building work in England that method is SAP (Approved Document L, paragraph 1.3). A householder extension is normally shown to comply another way: its new walls, roof, floor and windows meet limiting U-values, and its openings are no more than 25% of its floor area, with SAP as an alternative route (paragraphs 10.7 and 10.10).
If you are unsure which applies, we tell you at the quote. The answer depends on whether the work creates a new home.
Which edition of Part L applies?
Today the 2021 edition, with the 2023 amendments, applies (gov.uk). A 2026 edition takes effect in England on 24 March 2027 for most building work, and names two methodologies for new dwellings, the Home Energy Model and SAP (2026 edition). Transitional arrangements decide which edition governs a project that is already in the system, so the date your application is made matters.
We tell you which edition your project falls under, and the assessor works to it. If your build straddles the change, we say so before you submit.
- Applied now: the 2021 edition with 2023 amendments
- From 24 March 2027: the 2026 edition, for most work
- Dates of the application and start on site decide which applies
What to expect from the result
A first calculation often shows a gap: a little too much glazing, or a heating choice that scores badly. We use that to adjust the design in the drawings before they go to building control. For an existing house the limits are simple: roof 0.15, wall and floor 0.18, windows 1.4 (Table 4.2). They sit in the building regulations drawings, alongside any structural calculations. For a new home, see new build drawings.
What Part L sets, in figures
- SAP
- For a new dwelling the target primary energy rate, target emission rate and target fabric energy efficiency rate must be calculated using the government’s Standard Assessment Procedure, Appendix R. Approved Document L volume 1, 2021 edition with 2023 amendments, paragraph 1.3
- 0.15 / 0.18
- New fabric in an existing dwelling should achieve limiting U-values of 0.15 W/m²K for a roof and 0.18 for walls and floors. Approved Document L volume 1, 2021 edition, Table 4.2
- 1.4
- A new window should have a U-value of 1.4 W/m²K or better, or a minimum Window Energy Rating of Band B. Approved Document L volume 1, 2021 edition, Table 4.2
- 25%
- The total area of windows, rooflights and doors in an extension should not exceed 25% of the floor area of the extension, plus any openings the extension covers. Approved Document L volume 1, 2021 edition, paragraph 10.7
- 2.2
- A new rooflight is limited to a U-value of 2.2 W/m²K. Approved Document L volume 1, 2021 edition, Table 4.2
- 24 March 2027
- The 2026 edition of Approved Document L takes effect in England on 24 March 2027 for building work that is not higher-risk building work. Approved Document L volume 1, 2026 edition
- HEM or SAP
- The 2026 edition names two methodologies for a new dwelling: the Home Energy Model and the Standard Assessment Procedure. Approved Document L volume 1, 2026 edition, Regulation 24
- 5 weeks
- A full-plans building regulations application is decided within 5 weeks, or 2 months by agreement. gov.uk, Building regulations approval: how to apply
SAP and Part L questions
Do I need a SAP calculation for an extension?
Not usually. A householder extension is normally shown to meet limiting U-values for new fabric and an opening area of 25% of its floor area, which go on the drawings. A new dwelling or a conversion that creates one needs a SAP calculation.
Who carries out the calculation?
An accredited assessor, arranged by us. We brief them and return the result with the design changes it needs.
What U-values must new walls reach?
0.18 W/m²K for a wall or floor and 0.15 for a roof, when new fabric is added to an existing dwelling.
Is the 2026 edition in force yet?
It takes effect on 24 March 2027 in England for building work that is not higher-risk, subject to transitional arrangements.
Does the £225 cover the as-built certificate?
It covers the coordination of the design-stage calculation. If you need the as-built stage, we say so at the quote.
Other services people book with this one
- Building regulations drawings£479 drawings + £150 survey (£629 total)
- New build drawings£1,099 drawings + £150 survey (£1,249 total)
- Flat conversion drawings (two flats)£879 drawings + £150 survey (£1,029 total)
- Structural calculations£379
- Complete package: planning, building regulations and structural£1,209 drawings + £150 survey (£1,359 total)
Building a home or converting one?
Send the address and the drawings, if you have them. We reply with a fixed fee for the calculation.