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Southwark, London

SAP calculations in Southwark

SAP calculations in Southwark show building control that a conversion, an extension or a new home meets the energy rules, in a borough where few households live in a house. Fixed quote after a free constraints check, VAT included, with the calculation built on the same model as your drawings.

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 Southwark and the Householder SPD

    Southwark's design guidance for altering a home is the Householder development SPD, which sits under the Southwark Plan 2022. It governs how an addition looks. The energy rules govern how it performs, and a scheme in this borough has to satisfy both at the same moment.

    The numbers explain why that is hard here. Only 21.8 per cent of households live in a house or bungalow and just 28.9 per cent own their home, so much of our Southwark work is a flat, a maisonette or a loft above a shared stair, not a detached house with room to spare on every side.

    Those buildings have little to trade. A ground-floor flat extension has a small roof, a shared party wall and often a fixed rear elevation, so the energy calculation has to find its saving in the floor and the glazing. We run the numbers while the layout can still move, and we say plainly when a design needs a different window or a thicker floor build-up.

    Pencil resting on a dimensioned technical drawing beside a scale rule

    Local figures for Southwark

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Conservation areas53 named conservation areas published by the council—planning.data.gov.uk
    Article 4 directions480 Article 4 directions published by the council—planning.data.gov.uk
    Listed building entries919 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Households living in a house21.8 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Owner-occupied households28.9 % of households owner-occupied (owned outright or with mortgage/loan)Census 2021nomisweb.co.uk
    Householder applications granted94.8 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Average price, flat469,796 GBP2026-07publicdata.landregistry.gov.uk
    Mayoral CIL rate (indexed)72.73 £/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
    Circular 01/2026 (transitional arrangements)AD L/F 2021 continue where plans/notices are deposited before 24 Mar 2027 and work starts before 24 Mar 2028—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 Southwark
    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

    SAP calculations for Southwark extensions and roof work

    The limits for new elements in an existing home 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. A genuinely new roof or flank wall can reach them with a standard build-up.

    Glazing carries a ceiling too: 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. Rear additions to Victorian properties tend to want big glass openings to the garden, and the ceiling is usually the first constraint they meet.

    When a design cannot meet the individual limits, there is another way: 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 Southwark when the planning officer wants the rear glazing kept and the thickness of the wall is fixed by the party wall.

    Conservation, listing and Article 4 in Southwark

    Southwark has 53 conservation areas and 480 Article 4 directions, and Historic England lists 919 entries in the borough, 4 of them at Grade I and 30 at Grade II*. A SAP assessor can only assume what the officer will permit, so on any of these properties the heritage question comes before the heating question.

    On a listed building, internal insulation behind plaster or secondary glazing can touch protected fabric, and those choices go through consent. We feed the agreed specification into the calculation, not the other way round, so the numbers describe the building you will actually have.

    The borough decided 558 householder applications in its latest year and granted 94.8 per cent, with 95.3 per cent decided in time. Our planning drawings in Southwark cover the application, and a lawful development certificate in Southwark records a permitted scheme.

    New dwellings, conversions and the rule dates

    A new dwelling is assessed differently. The Approved Document L position is: 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's start is given as: AD L 2026 takes effect 24 Mar 2027 (24 Sep 2027 for higher-risk building work).

    Transitional rules decide which edition applies to your scheme: AD L/F 2021 continue where plans/notices are deposited before 24 Mar 2027 and work starts before 24 Mar 2028. For a house split into flats, or a yard turned into a mews home, the date the plans are deposited fixes the edition, so we settle it before the drawings are issued.

    Overheating is a separate duty: Approved Document O (overheating) applies to new residential buildings. A top-floor flat in a brick terrace is the usual case. At the end of construction: An energy performance certificate is required on construction of a new dwelling. A terraced house here averages £838,160 and a flat £469,796, so an accurate design-stage figure protects the value of the finished home.

    Cost, levies and the rest of the drawing set

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

    New floor area also attracts levies. The Mayoral charging band here is band 2, at an indexed £72.73 per square metre, and the borough's own schedule is the Southwark Community Infrastructure Levy (CIL) Charging Schedule, with residential rates of £598/m² (Zone 1); £300/m² (Zone 2); £74/m² (Zone 3). The zone depends on the address, so we confirm it with you early.

    For the beams that make an opening possible, see structural calculations in Southwark, and for the neighbouring borough, 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.
    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.

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    Questions

    Do I need SAP calculations for a flat conversion in Southwark?

    We confirm the route for your scheme at the free constraints check. For each new dwelling: For new dwellings AD L 2026 names two methods: the Home Energy Model (HEM) and SAP; validity dates are in the Notice of Approval.

    Which Southwark guidance covers home alterations?

    The Householder development SPD. Energy limits come from Approved Document L, not from the council.

    Can I keep original windows on a listed Southwark home?

    That is a listed building consent question first. Where an extension is involved, the energy rules allow other routes: Alternative routes: area-weighted U-value (para 10.9) or a SAP calculation against a notional extension (para 10.10).

    How much do SAP calculations cost in Southwark?

    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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