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Tower Hamlets, London

Basement impact assessments in Tower Hamlets

In Tower Hamlets the local plan asks for a basement impact assessment on every basement, with no size threshold, and flood risk is part of the test. Low-lying ground and a tight street pattern shape what the report must prove. We coordinate the report on 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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    Brick cottage with a tiled roof, chimneys and a front dormer window

    The basement impact assessment rule in Tower Hamlets

    The Tower Hamlets Local Plan 2031: Managing Growth and Sharing the Benefits, adopted in 2,020, does not sort basements into big and small. Its test is simple: All basements. The assessment has to show structural stability, flood safety and no adverse hydrogeological effect, and it must take account of the borough's strategic flood risk assessment.

    The plan goes further on use. A self-contained basement that has no access above the breach level of a flood is treated as a highly vulnerable use. A rentable lower-ground flat is therefore the hardest version of the idea in this borough, and we would tell you so at the free check.

    Householders face a second trigger in the council's checklist: Flood Zone 2 or 3 basement/ground floor extension. In those zones the flood risk assessment must cover every source of flooding, climate change, sustainable drainage and safe access and escape, which is a separate document that has to agree with the basement report.

    Rear view of brick terraced houses in London with slate roofs and chimney stacks along the shared roofline

    Local figures for Tower Hamlets

    Figures with their unit, period and source
    MeasureValuePeriodSource
    All basement developments must conduct a basement impact assessment showing structural stability, flood safety and no adverse hydrogeological impact, taking account of the Strategic Flood Risk Assessment. Self-contained basements without access above breach level are highly vulnerable use.All basements—towerhamlets.gov.uk, Tower Hamlets Local Plan 2031 (adopted 15 January 2020), Policy D.ES4, para 14.31, PDF p.162
    Householder applications in Environment Agency Flood Zone 2 or 3 that involve basement or ground floor extensions need a Flood Risk Assessment covering all forms of flooding, climate change, SuDS and safe access and egress.Flood Zone 2 or 3 basement/ground floor extension—towerhamlets.gov.uk, Householder Planning Application Checklist, September 2020, p.8 of 10, Flood Risk Assessment row
    Local planTower Hamlets Local Plan 2031: Managing Growth and Sharing the Benefits—towerhamlets.gov.uk
    Conservation areas59 named conservation areas published by the council—planning.data.gov.uk
    Listed building entries916 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Households living in a house12 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Domestic gardens share of land (GLUD 2005)7.4 % of land that is domestic garden (GLUD 2005)2005data.london.gov.uk
    Householder applications granted92.7 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Borough CIL residential rate£335.33/m² (Zone 1); £179.64/m² (Zone 2); £59.88/m² (Zone 3)rate for planning permissions granted 1 January to 31 December 2026 (schedule rates £280 / £150 / £50)towerhamlets.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 Tower Hamlets
    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

    Flats, terraces and tiny gardens

    Only 12 per cent of households here live in a house, and domestic gardens cover just 7.4 per cent of the borough's land. That is the opposite of a suburban dig. A basement is likely to be a lower-ground extension beneath a terrace, with a pavement vault or a lightwell instead of a lawn above.

    Heritage adds weight. The borough lists 59 conservation areas, 916 listed entries and 64 Article 4 directions, so a lightwell on a front elevation may need as much justification as the soil report.

    How Tower Hamlets treats householder schemes

    The council decided 191 householder applications in its latest year, granted 92.7 per cent and decided 95.8 per cent on time. Those are borough-wide rates, so treat them as context, not a prediction.

    What they suggest is a team that expects a complete pack on day one. We prepare the engineer's report, the flood evidence and our planning drawings in Tower Hamlets as one set, so every level, section and drain agrees across the sheets.

    Underpinning, levy and the neighbours' side

    Terraces share their foundations, so the Party Wall etc. Act matters more here than anywhere with detached homes. Section 6 says the Building owner may, and if the adjoining owner requires must, underpin or safeguard the adjoining foundations at own expense. Plan the budget for that, and for the surveyors.

    Levy is the other cost to price in. The borough charges £335.33/m² (Zone 1); £179.64/m² (Zone 2); £59.88/m² (Zone 3), in addition to the Mayor's levy of £72.73 per square metre indexed. Our structural calculations in Tower Hamlets page explains how the engineer's design fits the drawings.

    Narrow streets, vaults and construction access

    Streets here are narrow, so the engineer has to say how spoil leaves the site and how concrete arrives. Access shapes the choice between underpinning in sequence and a piled wall, because a lorry that cannot reach the front door makes hand-dug bays slower and dearer. The report should show where the temporary works sit, who is affected on the road and pavement, and how movement of the shared wall is monitored.

    We draw the construction sequence as numbered stages on one sheet, so the surveyor on the other side of the wall can follow it, and so the flood and drainage evidence can be checked against the same levels.

    Cost and the next step

    A basement here has no list price, because the flood zone, the depth and the use change the scope. The free check gives you a fixed quote and an honest view of whether the use you want is likely to be accepted.

    See the architectural drawings in Tower Hamlets overview, then compare Hackney and Newham, or the basement impact assessment national guide.

    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.
    Pencil resting on a dimensioned technical drawing beside a scale rule
    The street around you
    Move across the plinth — the blocks rise around the pointer.

    Other services in Tower Hamlets

    Basement impact assessments nearby

    Questions

    Does every basement in Tower Hamlets need an assessment?

    Yes, the local plan asks for a basement impact assessment on all basement developments, showing stability, flood safety and no adverse hydrogeological effect.

    Can I let a basement flat in Tower Hamlets?

    A self-contained basement without access above the flood breach level is treated as highly vulnerable, so it is the hardest case. We check the flood map before we advise.

    When is a flood risk assessment also needed?

    For householder basement or ground-floor extensions in the higher-risk flood zones, the council's checklist asks for one covering all forms of flooding.

    How much does it cost?

    A fixed quote after a free constraints check, because flood zone, depth and use change the scope.

    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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