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Hammersmith & Fulham, London

Basement impact assessment in Hammersmith and Fulham

Hammersmith and Fulham has no basement document with figures we can cite, yet it names a very large number of conservation areas. A basement impact assessment here is shaped by the street, not a formula. We are chartered architectural technologists and give a fixed quote after a free constraints check.

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 basement impact assessments

    Seven 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. Design options

      We model the house in Revit and show you options in 3D and plan, with the planning strategy and the precedents in your street.

    4. Design frozen

      You choose an option in writing. Nothing changes after this without your say.

    5. 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.

    6. Submission

      We prepare the forms, certificates, fee and documents and submit through the Planning Portal.

    7. Officer liaison

      We answer the planning officer and make any amendments within five working days, at no charge until approval.

    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

    How Hammersmith and Fulham treats a basement impact assessment

    Our research did not find a Hammersmith and Fulham policy that fixes a maximum depth, a garden percentage or a soil-cover figure for basements, and we found no council wording we could quote as a trigger for the assessment. We say that plainly because the neighbouring Royal Borough of Kensington and Chelsea does set firm numbers, and it is tempting to assume the same applies across the boundary. It does not.

    Next door, Kensington and Chelsea's guidance has limited a basement to no more than 50 per cent of each garden and asked for at least 1 metre of soil above the part beneath a garden. We use those figures as a benchmark when talking to clients near the boundary, not as a Hammersmith rule. Your own council judges the scheme under the London Plan's basement policy and the evidence you supply.

    That is why we begin with the council's validation list and the plot itself. We look at the depth you want, the closeness of neighbours, the conservation setting and the trees, then decide whether to scope a full assessment or a shorter structural and drainage statement.

    Rows of brick terraced houses and gardens on a residential street

    Local figures for Hammersmith & Fulham

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Conservation areas47 named conservation areas published by the council—planning.data.gov.uk
    Listed building entries268 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Heritage at Risk entries15 Heritage at Risk Register entries within the LPA boundary (Historic England)—planning.data.gov.uk
    Households living in a house24.6 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Householder applications granted97.8 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder applications decided in time79.8 % decided within 8 weeks or an agreed extended period1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    RBKC Basements SPD (April 2016) para 3.1 quoting Policy CL7(a): maximum 50% of each garden or open part of the site, measured separately for each garden (PDF p.12)50 %—rbkc.gov.uk
    Approved Document C (2004 ed. incl. 2010/2013) para 3.2: where the water table can rise to within 0.25 m of the lowest floor, drain by gravity or other effective means; para 3.4 groundwater stability; basement walls under groundwater pressure covered in the walls section0.25 m—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 Hammersmith & Fulham
    Which application your project needsLawful Development Certificate decision: 8 weeks. Prior approval decision: 42 days. Householder decision: 8 weeksYour projectWithin permitted development?Lawful Development CertificatePrior approvalHouseholder applicationYesLarger rear extensionNoABC

    Which application your project needs

    The usual route for a house; flats and listed buildings follow other rules.

    A · Lawful Development Certificate decision
    8 weeks
    B · Prior approval decision
    42 days
    C · Householder decision
    8 weeks

    Conservation and listed stock in the borough

    The council names 47 conservation areas and holds 268 listed building entries, with 15 entries on the Heritage at Risk Register. For a compact borough, that is a great deal of protected street. A basement in a conservation area draws attention to every visible change: lightwell railings, rooflights at pavement level and front garden loss.

    Only 24.6 per cent of households live in a house or bungalow, and owner-occupation is 32.1 per cent, so houses suitable for dig-down work are scarce and often high value. Gardens make up 17.1 per cent of land, a small share that limits how much of the plot a basement can sensibly take.

    The council decided 506 householder applications in the latest year and granted 97.8 per cent, though only 79.8 per cent were decided in time. Build some slack into your programme, because a basement pack that prompts a request for more information stops the clock while the extra evidence is gathered.

    Reading the street before drawing the basement

    A conservation street in this borough has a visible character: matching front areas, railings, steps and a continuous building line. A basement that leaves the front untouched and puts the lightwell at the rear is the version most likely to sit comfortably with that. Where the front must change, we draw the proposed railings and any pavement-level rooflight carefully, because the conservation officer will read them first.

    The neighbouring borough's figures are a useful guide for sizing the box, but the garden and soil limits still have to be judged against your own council's view. We therefore treat the Kensington and Chelsea numbers as a cautious ceiling and test the design against your officer's likely questions.

    What the assessment shows and who writes it

    It shows structural stability, groundwater flow and surface water are unharmed by the new floor. A ground investigation firm and a structural engineer write the specialist parts, and we draw the plans and sections they rely on and coordinate the whole pack. See our structural calculations page for the engineer's role. On a terrace, the engineer's temporary works sequence matters as much as the finished box, and we show it on the drawings.

    Approved Document C expects a drained floor where the water table can rise to within 0.25 metres of it.

    Party walls, planning route and cost

    Under the Party Wall etc. Act 1996, a dig within 3 metres of an adjoining building and below its foundations needs a notice, as does one within 6 metres on the 45-degree test. Our party wall notices service prepares the drawings.

    Planning drawings come from our planning drawings work. For the borough's figures see architectural drawings in Hammersmith and Fulham. Kensington and Chelsea is covered at architectural drawings in Kensington and Chelsea.

    The service is unpriced. After the free constraints check you receive a fixed quote.

    What you receive

    Planning drawing sheet for a rear extension with plans, elevations and sections
    Sample drawing. Planning drawings for a rear extension: plans, elevations and sections on one sheet set.
    Georgian brick terrace with sash windows, arched fanlight doorways, stone steps and iron railings in London
    The street around you
    Move across the plinth — the blocks rise around the pointer.

    Other services in Hammersmith & Fulham

    Basement impact assessments nearby

    Questions

    Does Hammersmith and Fulham follow Kensington and Chelsea's basement limits?

    No. We found no equivalent Hammersmith and Fulham figures. Kensington and Chelsea's numbers are a useful benchmark, not a rule for this borough.

    Will a conservation area affect my basement?

    It brings closer scrutiny of lightwells and front gardens. The borough names 47 conservation areas, so we check yours early.

    Does the borough decide quickly?

    It grants most householder applications, but only 79.8 per cent were decided in time in the latest year, so allow extra time.

    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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