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Lewisham, London

Basement impact assessment in Lewisham

A basement impact assessment in Lewisham is the report that shows a new lower floor is safe for the ground, the water and the neighbours. Lewisham caps basements by storey and by distance from the rear wall, and its many Article 4 directions often reach the front of the house, so we check both on a fixed quote after a free constraints check.

Fixed quote after a free constraints check

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  • LABC Partnered
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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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    What Lewisham asks for with a basement impact assessment

    Lewisham's basement geometry reads: one storey; 3 m or 1/4 garden, the rear projection being the lesser of the two measures from the original rear wall, lightwells included. Front lightwells have their own set of limits: 1.5 m; 1/3 width; 1/4 garden; 2.4 m; 1 m soil. We found no Lewisham item that names a stand-alone basement impact assessment, so we read the current validation list for your address and tell you in writing what it expects.

    In practice that conversation covers four things: whether the council wants a report at all for the depth you have in mind, who must sign it, how much ground investigation is expected, and whether the heritage constraints on your street change the answer. For a modest lowering of an existing cellar, the honest answer may be that a lighter report is enough.

    Whatever the requirement, the assessment goes in with the planning application, and the plans, the sections and the engineer's findings have to agree on depth, drainage and method.

    Rows of brick terraced houses and gardens on a residential street

    Local figures for Lewisham

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Basements should generally be no more than one storey below the original ground floor, and including lightwells no wider than the original property nor more than 3 m from the original rear wall or a quarter of the original garden length, whichever is less.one storey; 3 m or 1/4 garden—lewisham.gov.uk, Lewisham Alterations and Extensions SPD 2019, p.44, paras 4.8.8-4.8.9
    Article 4 directions57 Article 4 directions published by the council—planning.data.gov.uk
    Article 4 direction areas89 Article 4 direction area polygons published by the council—planning.data.gov.uk
    Conservation areas30 named conservation areas published by the council—planning.data.gov.uk
    Listed building entries367 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Heritage at Risk entries21 Heritage at Risk Register entries within the LPA boundary (Historic England)—planning.data.gov.uk
    Domestic gardens share of land (GLUD 2005)31.1 % of land that is domestic garden (GLUD 2005)2005data.london.gov.uk
    Households living in a house42.2 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Householder applications granted89.4 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder applications decided in time95.2 % decided within 8 weeks or an agreed extended period1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Party Wall etc. Act 1996 s6(1): excavation within 3 m horizontally of an adjoining owner's building or structure and deeper than the bottom of its foundations3 m—legislation.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 Lewisham
    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

    Article 4 and heritage in Lewisham

    Lewisham holds 57 directions covering 89 separate areas. Many remove permitted development rights from the front of a house, which is where a basement lightwell would go. Check the direction first, because it can turn a minor-looking change into one that needs permission in its own right.

    The borough also has 30 conservation areas, 367 listed building entries and 21 entries on the Heritage at Risk Register. In a conservation area the council looks at what the lightwell does to the street, and for a listed house the heritage case has to be written into the same submission as the engineering.

    Ground, gardens and homes in Lewisham

    Domestic gardens make up 31.1 per cent of the borough's land in the national land-use database, which is why rear-garden basements and garden-level extensions are common briefs here. 42.2 per cent of households live in a house and 41.9 per cent own their home.

    More garden does not mean simpler ground. Groundwater and stability depend on the soil under your own plot, and we write the ground investigation brief around the real site, not a template. The three themes are always the same: stability of the soil and neighbouring walls, groundwater, and surface water or flood risk.

    How Lewisham decides householder applications

    In its latest published year the council decided 1,256 planning applications. It granted 89.4 per cent of householder applications and 83.7 per cent of minor ones, and 95.2 per cent of householder decisions were made within the statutory period or an agreed extension. These rates cover every project type, so they do not say how a basement will fare, but they do show the council keeps to time.

    A basement is judged together with whatever you build above it. Our planning drawings in Lewisham page covers the main set, and if the scheme includes a new floor in the roof as well, our loft conversion drawings in Lewisham explain how the two fit together.

    Party wall and Building Regulations duties in Lewisham

    Digging beside a neighbour needs a notice under the Party Wall etc. Act 1996 when the excavation is within 3 metres of an adjoining building and deeper than its foundations, or within 6 metres on the diagonal test. Serve it at least 1 month before work. Our party wall notices service prepares the plans.

    Where the water table can rise to within 0.25 metres of the lowest floor, Building Regulations require the floor to be drained or protected. Our structural calculations in Lewisham page explains how the engineer's design meets our drawings.

    Who does the work and what it costs

    We are chartered architectural technologists (MCIAT). We draw the scheme, commission the structural engineer and the ground investigation, and assemble the report so every document matches. The price depends on depth, ground and heritage, so after the free constraints check we send a fixed quote and a plain account of what Lewisham is likely to want.

    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 Lewisham

    Basement impact assessments nearby

    Questions

    Does Lewisham require a basement impact assessment?

    We found no stand-alone assessment item, though the geometry limits apply: one storey; 3 m or 1/4 garden. We check the current list for your address and tell you before you commit.

    Does Article 4 affect a Lewisham basement?

    It can. With 57 directions in the borough, a lightwell on the front of a house is often where permitted development rights have been removed.

    Do I need a party wall notice in Lewisham?

    Usually, if the dig is within 3 metres of a neighbour's building and deeper than its foundations, or within 6 metres on the diagonal test.

    What does a Lewisham assessment cost?

    It depends on depth, ground and heritage. You receive a fixed quote after a free constraints check.

    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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