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Barnet, London

SAP calculations in Barnet

SAP calculations in Barnet are the energy assessments building control can ask for on an extension or a new home, and we fit them to your drawings from the same model. Fixed quote after a free constraints check, VAT included.

Fixed quote after a free constraints check

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    Architectural model of a four-storey London stucco townhouse in its terrace, with a portico, area railings, sash windows, a cornice and chimney stacks
    The house as it stands: four storeys over a lower ground floor.Existing Proposed worksAn illustrative model, built for this page.

    How we work on sap calculations

    Five steps from first call to approval.

    The same model cut through the middle: every floor, the stair, the chimney breasts, the new mansard, rear extension and basement in section
    Section through the model: every floor on one datum.

    1. Enquiry and constraints check

      We check the property against conservation areas, listed status, Article 4 directions, tree preservation orders, flood zone and planning history. We choose the right route and send a fixed quote.

    2. Measured survey

      We survey the house on one datum: rooms, levels, boundaries, drains, trees and the neighbours' windows that the 45° and 25° tests depend on.

    3. Independent check

      A second chartered technologist checks every sheet against the council's validation checklist and the policy. A senior review signs it off before anything is submitted.

    4. Building regulations

      Technical drawings are coordinated with the structural engineer's calculations, the drainage and the planning conditions.

    5. Approval and hand-over

      Building control approval, then a next-steps pack covering the commencement notice, party wall timing and CIL.

    Free redraws until approval. Every drawing set is checked independently, and the checker is never the person who drew it.

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    House extension under construction with scaffolding, new glazed doors and building materials

    SAP calculations in Barnet and the council's design guide

    Barnet's guidance for extending a house is Part 4 of its design series: the Sustainable Design and Development Guidance SPD, Part 4: Guidance on residential extensions and alterations, which belongs to the Barnet Local Plan 2021-2036. It deals with appearance, bulk and neighbours. It leaves the energy figures to the Building Regulations, so a scheme can be acceptable to the planning officer and still fail on heat loss.

    The two documents pull in slightly different directions. The planning guide favours a modest, subordinate extension. The energy rules favour thicker walls and roofs. Where the plan is tight against a boundary, a few extra centimetres of insulation can push the wall into the neighbour's side, and we catch that on the survey drawing, not on site.

    Barnet's gardens are generous: 28.1 per cent of the borough's land is domestic garden. Long plots invite deep extensions with large areas of glass, and that is where an energy calculation earns its fee.

    Pencil resting on a dimensioned technical drawing beside a scale rule

    Local figures for Barnet

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Conservation areas16 named conservation areas published by the council—planning.data.gov.uk
    Article 4 directions15 Article 4 directions published by the council—planning.data.gov.uk
    Article 4 direction areas48 Article 4 direction area polygons published by the council—planning.data.gov.uk
    Green Belt share of the council area28 % of council area covered by green-belt polygons—planning.data.gov.uk
    Householder applications granted80.2 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder appeals allowed50.6 % of householder appeals alloweddecision dates 1 Jul 2021 to 30 Jun 2026assets.publishing.service.gov.uk
    Domestic gardens share of land (GLUD 2005)28.1 % of land that is domestic garden (GLUD 2005)2005data.london.gov.uk
    Approved Document L Vol 1 2021 incl. 2023 amendments, Table 4.2New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4—gov.uk
    Approved Document L Vol 1 2021, para 10.7(d)Windows, roof windows, rooflights and doors in an extension should not exceed 25% of the extension floor area plus the area of openings removed or covered—gov.uk
    AD L Vol 1 2026, p.2AD L 2026 takes effect 24 Mar 2027 (24 Sep 2027 for higher-risk building work)—gov.uk

    A blank value means the figure has not been published, not that there are none. Check your own address with the council.

    Councils bordering Barnet
    Building regulations, layer by layerPart A: structure: Approved Document A: Structure, 2004 edition incorporating 2004, 2010 and 2013 amendments. Part B: fire safety: All dwellings: fire detection and alarm system minimum Grade D2 Category LD3 (BS 5839-6), mains-operated smoke alarms to BS EN 14604. Part L: insulation: New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4. Part K: stairs: 2.0 m clear headroom over stairs. Full plans application: Building control body must decide a full plans application within 5 weeks, or longer if agreed in writingPart A: structurePart B: fire safetyPart L: insulationPart K: stairsFull plans applicationABCDE

    Building regulations, layer by layer

    The Approved Documents that shape most house projects, from structure to the application itself.

    A · Part A: structure
    Approved Document A: Structure, 2004 edition incorporating 2004, 2010 and 2013 amendments
    B · Part B: fire safety
    All dwellings: fire detection and alarm system minimum Grade D2 Category LD3 (BS 5839-6), mains-operated smoke alarms to BS EN 14604
    C · Part L: insulation
    New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4
    D · Part K: stairs
    2.0 m clear headroom over stairs
    E · Full plans application
    Building control body must decide a full plans application within 5 weeks, or longer if agreed in writing

    Glazing, U-values and the three routes

    For new parts of an existing house the limits are: New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4. These are a ceiling on heat loss from each element, and a standard cavity wall extension with modest windows will usually comply without further work.

    Glass is the usual stumbling block. The rule reads: Windows, roof windows, rooflights and doors in an extension should not exceed 25% of the extension floor area plus the area of openings removed or covered. A rear extension with a full-width glazed wall and a roof lantern can exceed it comfortably, and the extension is then judged by another method.

    Those methods are: Alternative routes: area-weighted U-value (para 10.9) or a SAP calculation against a notional extension (para 10.10). We usually run the area-weighted check first because it is quick, and move to SAP only when the design needs the extra room to trade glass against insulation.

    Barnet's planning record and heritage constraints

    Barnet decided 1,361 householder applications in its latest year, granting 80.2 per cent, with 95.1 per cent in time. Appeals tell a further story: of 413 householder appeals decided over five years, 50.6 per cent were allowed. A consistent, complete application is worth the effort.

    The borough has 16 conservation areas and 15 Article 4 directions covering 48 mapped areas, and a little over a quarter of the borough, 28 per cent, is Green Belt. In the Green Belt and in a conservation area, changes to windows and roofs are examined closely, and the energy design must respect them.

    Where permitted development applies, a lawful development certificate in Barnet records it. Where it does not, planning drawings in Barnet set out the householder application, and the energy route is decided before either is submitted.

    New homes, conversions and the coming energy rule change

    A new home follows a different path. The guidance states: For new dwellings AD L 2026 names two methods: the Home Energy Model (HEM) and SAP; validity dates are in the Notice of Approval. If you are subdividing a large plot or converting a house into flats, your assessor will need to know which edition applies on the day plans are deposited.

    The start of the next edition is given as: AD L 2026 takes effect 24 Mar 2027 (24 Sep 2027 for higher-risk building work). The transition rule says: AD L/F 2021 continue where plans/notices are deposited before 24 Mar 2027 and work starts before 24 Mar 2028. A project that goes in early keeps the existing method, one that goes in late must follow the new one, and the difference can be material.

    Overheating is separate again. The relevant rule is that Approved Document O (overheating) applies to new residential buildings. A south-facing glazed extension on a new dwelling will draw questions about shade and openable areas, and we plan for them from the start.

    Price, programme and what comes next

    Our SAP work is quoted rather than listed, because an extension check and a new dwelling assessment are very different jobs. You will have a fixed quote after a free constraints check, VAT included, before anything is committed.

    The assessor uses our model, so the figures match the drawings. The same sheets support the technical submission in building regulations drawings in Barnet, and the cost of the local levy is the next question: the borough's schedule is the Barnet CIL Charging Schedule (approved by Council 1 March 2022), with a residential rate of £361.44/m² indexed 2026 (schedule rate £300/m², residential incl. C2, C3, C4 and sui generis HMOs).

    For the wider picture see architectural drawings in Barnet, or compare a neighbouring borough such as SAP calculations in Camden.

    What you receive

    Building regulations section drawing showing the construction build-up
    Sample drawing. Building regulations section showing construction build-up for a building control check.
    Red-brick English house with rows of solar panels on its tiled roof
    Energy in
    Move the pointer up — the plug rises toward the socket.

    Other services in Barnet

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    Questions

    Which Barnet document covers extending a house?

    Part 4 of the council's design series, the Sustainable Design and Development Guidance SPD, Part 4: Guidance on residential extensions and alterations. It does not set energy figures, which come from Approved Document L.

    Does a Barnet extension need a SAP calculation?

    Not always. If the new elements meet the limits and the glazing stays in its cap, no. If they do not, a SAP calculation is the route that lets the design stand.

    What happens if I start work after the rule change?

    AD L/F 2021 continue where plans/notices are deposited before 24 Mar 2027 and work starts before 24 Mar 2028. We confirm which edition applies to your project in the first call.

    How much does a SAP calculation cost in Barnet?

    Fixed quote after a free constraints check, VAT included.

    Sources and dates

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    Tell us about your property.

    We check the constraints, then send a fixed fee. Messages before 3pm get a reply the same working day.

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