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City of London, London

SAP calculations in the City of London

SAP calculations in the City of London serve a very particular housing stock: flats in towers, conversions above offices and homes inside listed estates. We prepare the energy evidence from your drawings, with a fixed quote after a free constraints check, VAT included.

Fixed quote after a free constraints check

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  • £2m PI insured
  • LABC Partnered
  • Fixed fees, VAT included

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

    SAP calculations in the City of London: a small, unusual housing stock

    The Square Mile has only 4,914 households, and just 2 per cent of them live in a house or bungalow. Nearly all homes are flats, so an extension in the ordinary sense is rare here. Most calculations we prepare concern new flats created by conversion, or alterations to a single flat inside a larger building.

    The council's planning framework is the City of London Local Plan 2015. For one residential landmark it also publishes a specific document: the Barbican Estate Listed Building Management Guidelines: Volume I Introduction and Volume II Residential (SPD). Anyone altering a flat in that estate works under it, and the energy upgrade has to respect the listed fabric.

    Because there is so little residential floor area, a single project can matter. A change to a flat's windows or ventilation in a listed block may need consent, and the SAP assumptions have to be those that consent allows.

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

    Local figures for City of London

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Households4,914Census 2021 (21 March 2021)nomisweb.co.uk
    Households living in a house2 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Conservation areas28 named conservation areas published by the council—planning.data.gov.uk
    Listed building entries637 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Grade I listed entries86 list entries—planning.data.gov.uk
    Article 4 directions1 Article 4 directions published by the council—planning.data.gov.uk
    Average price, flat709,939 GBP2026-07publicdata.landregistry.gov.uk
    AD L Vol 1 2026, regulation 24 intention (p.11)For new dwellings AD L 2026 names two methods: the Home Energy Model (HEM) and SAP; validity dates are in the Notice of Approval—gov.uk
    Approved Document O 2021, para 0.3Approved Document O (overheating) applies to new residential buildings—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 City of London
    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

    Conversions and new flats

    A flat created by converting an office or a commercial floor is assessed as a new dwelling. The guidance says: 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 edition that applies depends on dates: AD L 2026 takes effect 24 Mar 2027 (24 Sep 2027 for higher-risk building work).

    The transition rule is: AD L/F 2021 continue where plans/notices are deposited before 24 Mar 2027 and work starts before 24 Mar 2028. For a conversion the timing matters, because deposit and start dates are fixed by the programme of the whole building, not by the individual flat.

    Summer comfort is the other concern in a dense urban setting. The rule is that Approved Document O (overheating) applies to new residential buildings. A flat with large glazed façades and little cross-ventilation needs shading and openable areas planned from the outset, and we coordinate that with the façade design.

    Heritage density across the Square Mile

    The City has 28 conservation areas and 637 listed building entries, of which 86 are Grade I. For such a small borough that is a very high concentration of protected fabric, and it governs any change to windows, roofs or façades.

    There is 1 Article 4 direction in force. Where one applies, permitted development rights are withdrawn for the covered works, and a change that would be routine elsewhere needs an application.

    Householder activity is almost nil: the council recorded just 1 householder decision in its latest year. Our planning work here is mostly for conversions and flat alterations; see planning drawings in the City of London for how we handle them, or a lawful development certificate in the City of London where rights exist.

    Energy limits when work is to part of an existing building

    Where a project adds a new element, such as a roof-top extension to a flat or a replacement window, the limits apply to that element. They 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.

    Glazing has its own cap on the simple route: 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. Heritage consent for windows can complicate it, and the alternatives are: Alternative routes: area-weighted U-value (para 10.9) or a SAP calculation against a notional extension (para 10.10).

    We pick the route to suit the consent, and where a listed window is kept, the calculation carries the balance elsewhere.

    Price, levies and what goes with the calculation

    Our fee is a fixed quote after a free constraints check, VAT included, so you know it before committing. The assessor uses our model, so the figures match the drawings, and the same sheets support building regulations drawings in the City of London.

    New floor area is subject to levy. The City's schedule is the City of London Community Infrastructure Levy Charging Schedule, with rates of £251.05/m² (Riverside); £159.00/m² (Rest of City) [schedule rates £150 and £95]. We note the area on each plan to help you estimate the cost.

    The average flat price in the borough is £709,939. See architectural drawings in the City of London for the full range we offer, or compare SAP calculations in Westminster next door.

    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.
    Pencil resting on a dimensioned technical drawing beside a scale rule
    Energy in
    Move the pointer up — the plug rises toward the socket.

    Other services in City of London

    SAP calculations nearby

    Questions

    Do flat conversions in the City of London need a SAP calculation?

    Yes, a new dwelling is assessed by a calculation method. The guidance says: 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 City document covers the Barbican?

    The Barbican Estate Listed Building Management Guidelines: Volume I Introduction and Volume II Residential (SPD).

    Does heritage affect the energy design?

    Yes. The borough has 637 listed building entries, and consent limits what can be changed.

    How much does it cost?

    Fixed quote after a free constraints check, VAT included.

    Sources and dates

    City of London skyline glowing at dusk across the Thames under a dramatic orange sky

    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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