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Wandsworth, London

SAP calculations in Wandsworth

SAP calculations in Wandsworth show building control that a loft, a rear extension or a new home meets the energy rules, in a borough where high property values make every extra room worth building well. 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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    Pencil resting on a dimensioned technical drawing beside a scale rule

    SAP calculations in Wandsworth and the Housing SPD

    Wandsworth bundles its extension guidance into one document: the Housing SPD (covers rear extensions, basements, roof extensions and loft conversions). A separate note, the Basement extensions guidance (non-statutory), deals with digging down. Both sit under the Wandsworth Local Plan 2023-2038, adopted in 2,023. Because one document governs rear extensions, roofs and basements, one calculation often has to serve several of those at once.

    A typical Wandsworth scheme does exactly that. A house on a Battersea or Putney street may gain a rear addition, a loft room and a lowered floor in a single project. Each adds a different kind of new element, a wall, a roof and a floor, and the calculation has to set all three against the existing house together rather than one at a time.

    Only 31.4 per cent of households live in a house or bungalow and 42.5 per cent own their home, so the houses that exist are prized. A terraced house averages £970,844 and a detached house £2,495,892, and at those values owners invest in the full package of upgrades.

    Red-brick English house with rows of solar panels on its tiled roof

    Local figures for Wandsworth

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Conservation areas46 named conservation areas published by the council—planning.data.gov.uk
    Listed building entries312 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Householder applications granted91.9 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder decisions977 decisions1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Households living in a house31.4 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Average price, terraced970,844 GBP2026-07publicdata.landregistry.gov.uk
    Average price, detached2,495,892 GBP2026-07publicdata.landregistry.gov.uk
    Mayoral CIL rate (indexed)96.97 £/m² (indexed, permissions granted in 2026)—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

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

    Councils bordering Wandsworth
    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

    Energy limits for Wandsworth lofts, rear additions and floors

    The limits for new elements 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. The roof figure is the hardest one for a loft conversion, since the build-up has to fit inside the rafter depth while still meeting it.

    Glazing carries a ceiling: 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. Roof glazing and a wall of doors to the garden both count towards it.

    When the simple limits do not fit, the alternatives are: Alternative routes: area-weighted U-value (para 10.9) or a SAP calculation against a notional extension (para 10.10). We use the comparison route in Wandsworth when a loft needs a long dormer window or when an old rear wall limits what the new work can offset. We explain the reasoning in the report so the building control officer can follow it.

    Wandsworth planning figures and heritage

    Wandsworth has 46 conservation areas and Historic England lists 312 entries, 5 at Grade I and 34 at Grade II*. The borough has no Green Belt, at 0 per cent, and domestic gardens take 21.5 per cent of its land.

    The council decided 977 householder applications in its latest year and granted 91.9 per cent, with 92.4 per cent decided in time. Minor applications ran at 86.7 per cent granted across 902 decisions.

    On larger home extension prior approvals, the council granted 13 and refused 12. For most Wandsworth projects, our planning drawings in Wandsworth are the route, and a lawful development certificate in Wandsworth records a permitted scheme.

    New dwellings, rule dates and certificates

    The calculation starts from a survey of the existing house: wall construction, roof insulation, glazing and the heating system. Those facts set the baseline against which the new loft, extension or floor is judged. Drawings and calculation are checked by a second person before they reach you, and the figures are reconciled with the plans at the same time.

    A new dwelling follows a separate path: For new dwellings AD L 2026 names two methods: the Home Energy Model (HEM) and SAP; validity dates are in the Notice of Approval. The next edition: AD L 2026 takes effect 24 Mar 2027 (24 Sep 2027 for higher-risk building work).

    The transition rule: AD L/F 2021 continue where plans/notices are deposited before 24 Mar 2027 and work starts before 24 Mar 2028. A house converted into flats, or a garage turned into a home, depends on the deposit date. For overheating: Approved Document O (overheating) applies to new residential buildings.

    At the end of construction, An energy performance certificate is required on construction of a new dwelling. A flat in the borough averages £526,813, and prices have changed by -5.5 per cent over twelve months, so buyers will read the certificate.

    Cost, levies and the drawings alongside

    You get a fixed quote after a free constraints check, VAT included, before you commit. The assessor uses our model, so the figures match your drawings, and the result supports your submission in building regulations drawings in Wandsworth.

    The Mayoral charging band here is band 1, at an indexed £96.97 per square metre. Wandsworth also applies the Wandsworth CIL Charging Schedule, which varies by area: £1,031.39/m² (Nine Elms Residential Area A); £475.34/m² (Nine Elms Residential Area B); £0 (Roehampton Charging Area); £448.43/m² (all other areas).

    For the beams behind an opening, see structural calculations in Wandsworth, and for the neighbouring borough to the east, compare SAP calculations in Lambeth.

    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.
    House extension under construction with scaffolding, new glazed doors and building materials
    Energy in
    Move the pointer up — the plug rises toward the socket.

    Other services in Wandsworth

    SAP calculations nearby

    Questions

    Which Wandsworth document covers lofts and rear extensions?

    The Housing SPD (covers rear extensions, basements, roof extensions and loft conversions). Basements have their own note, the Basement extensions guidance (non-statutory).

    Does a loft conversion in Wandsworth need a SAP calculation?

    Not always. The routes are: Alternative routes: area-weighted U-value (para 10.9) or a SAP calculation against a notional extension (para 10.10).

    What Mayoral CIL band is Wandsworth in?

    Band 1, at an indexed £96.97 per square metre.

    How much do SAP calculations cost in Wandsworth?

    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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