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Islington, London

SAP calculations in Islington

A SAP calculation in Islington is the energy assessment for a new home or a flat created inside an existing building, and sometimes for a rear extension. We coordinate it with an assessor and your drawings, for a fixed quote after a free constraints check. Only 16.3 per cent of households here live in a house, so most of our energy work is on flats, conversions and small infill.

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

    Islington's design guidance next to the energy rules

    Islington's design expectations are in the Islington Urban Design Guide SPD, and the Basement Development SPD sits beside it for anything below ground. Both work under the Islington Local Plan: Strategic and Development Management Policies, Site Allocations, and Bunhill and Clerkenwell Area Action Plan, adopted in 2,023. These are planning documents about appearance, neighbours and structure. They do not replace the energy submission that building control reads.

    For energy, the relevant test is Part L of the Building Regulations. We keep the two apart on purpose, because the planning officer and the building control surveyor ask different questions of the same drawings.

    We do not quote an Islington-only energy figure, as the council publishes none that we could cite. Our practice is to read the local plan for the site and then design to the national limits.

    Pencil resting on a dimensioned technical drawing beside a scale rule

    Local figures for Islington

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Households living in a house16.3 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Owner-occupied households26.7 % of households owner-occupied (owned outright or with mortgage/loan)Census 2021nomisweb.co.uk
    Households96,496Census 2021 (21 March 2021)nomisweb.co.uk
    Average price, flat560,124 GBP2026-07publicdata.landregistry.gov.uk
    Average price, terraced1,151,398 GBP2026-07publicdata.landregistry.gov.uk
    Conservation areas41 named conservation areas published by the council—planning.data.gov.uk
    Listed building entries1,050 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Grade II listed entries1,002 list entries—planning.data.gov.uk
    Householder decisions337 decisions1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder applications granted92.6 %1 July 2025 - 30 June 2026assets.publishing.service.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 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 Islington
    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

    Flats, conversions and the SAP calculation in Islington

    Islington is a borough of flats. Its households total 96,496, and the owner-occupied share is only 26.7 per cent. A flat averaged £560,124 in the latest Land Registry figures, against £1,151,398 for a terraced house, so a house is the exception and a prized one.

    When a house is split into flats, or a building gains new dwellings, the new homes are assessed as dwellings rather than as extensions. For the method on new homes the guidance reads: 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 weighing a split, our flat conversion drawings in Islington set out the layout, and the energy information follows from the same set.

    Extending an Islington terrace

    Where the house is a terrace, a rear or side-return extension is the usual project. The limiting values for new elements in existing homes 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 glazed side return is attractive and quickly runs into the opening limit, which is worded as: 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.

    At that point the choice is a smaller opening or a calculation that trades fabric performance against glass. We run that comparison before the planning drawings are issued, so the choice is made once. Our side return extension drawings in Islington carry that decision.

    Heritage, basements and what they do to the energy design

    Islington has 41 conservation areas and 1,050 list entries, of which 1,002 are Grade II. Insulation and window changes on a protected front elevation are limited, and the energy design has to respect that. Approved Document L gives historic buildings special consideration, so we agree the approach early rather than assuming a standard solution.

    Basements are a particular case. Extra floor area under a house changes heat loss through the ground, and the council's basement guidance adds structural and water tests. We design those together so that one change does not undo the other.

    Islington's decisions and your timetable

    Islington decided 337 householder applications in its latest published year, granting 92.6 per cent and deciding 98.8 per cent in time. Those are householder figures only, and they do not cover new dwellings or conversions, which take longer and face more conditions.

    For timing on larger work, note that the standard moves in time: AD L 2026 takes effect 24 Mar 2027 (24 Sep 2027 for higher-risk building work). The transitional rule is: AD L/F 2021 continue where plans/notices are deposited before 24 Mar 2027 and work starts before 24 Mar 2028. We confirm which standard your scheme falls under, and link it to the building regulations drawings in Islington.

    Next steps and neighbouring boroughs

    For the full picture of the borough start at architectural drawings in Islington. The same energy question in the next boroughs is covered in SAP calculations in Hackney and 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 Islington

    SAP calculations nearby

    Questions

    Does a flat conversion in Islington need a SAP calculation?

    Yes, usually. New dwellings created by conversion are assessed as dwellings, and building control expects the energy evidence with the submission.

    Do Islington's design guides ask for SAP calculations?

    They are planning guides. The Islington Urban Design Guide SPD covers design, and energy compliance is dealt with under the Building Regulations.

    Are listed buildings in Islington exempt from the energy rules?

    Not automatically. Historic buildings get special consideration, but each case is judged on the work proposed. We check this before quoting.

    How much do SAP calculations cost in Islington?

    A fixed quote follows a free constraints check, because the price depends on the number of dwellings and the complexity of the design.

    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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