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Haringey, London

Basement impact assessment in Haringey

Haringey asks for a basement impact assessment on every application that proposes a new basement, including extensions to an existing one. The Development Management DPD sets the test, and the stages must be done by a qualified independent assessor paid for by the applicant. We are chartered architectural technologists and give a 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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    Rear view of brick terraced houses in London with slate roofs and chimney stacks along the shared roofline

    Haringey's rule for a basement impact assessment

    Haringey's Local Validation List says an assessment, carried out by a qualified and recognised assessor, is required for all applications proposing new basement development, extensions to existing basements included. The validation list is the gate: without the report an application is not registered, and the decision clock never starts.

    The test it must satisfy is the basement policy in the Development Management DPD. It permits basements only where they do not harm structural stability, do not increase flood risk and, under gardens, keep adequate soil depth and avoid tree loss. The policy has no numeric garden percentage, depth or storey limit. The supporting text says the assessment stages are done by qualified independent assessors paid for by the applicant, so the report must come from someone with no stake in the design.

    That absence of a number cuts both ways. There is no formula to design to, and the officer judges the evidence. We therefore keep the architecture modest where the report is thin and bring in the independent assessor early, so the design and the report support each other rather than argue.

    Pencil resting on a dimensioned technical drawing beside a scale rule

    Local figures for Haringey

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Basement Impact Assessment, carried out by a qualified and recognised assessor, is required for all applications proposing new basement development (including extensions to existing basements), to show compliance with the current policy (DM18).All basement applications—haringey.gov.uk, Haringey Local Validation List (planning validation checklist, effective 29 August 2024), pdf p.9, row 'Basement Impact Assessment'
    DM18 only permits basements that do not harm structural stability, do not increase flood risk, and (under gardens) keep adequate soil depth and avoid loss of trees. Para 3.45: BIA stages are done by qualified independent assessors paid for by the applicant. DM18 has no numeric garden-percentage, depth or storey limit.No numeric limit in DM18—haringey.gov.uk, Haringey Development Management DPD (2017), Policy DM18 A(a)-(i), paras 3.42-3.46 (printed p.38, PDF p.40)
    Conservation areas33 named conservation areas published by the council—planning.data.gov.uk
    Article 4 directions25 Article 4 directions published by the council—planning.data.gov.uk
    Listed building entries289 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Domestic gardens share of land (GLUD 2005)26.6 % of land that is domestic garden (GLUD 2005)2005data.london.gov.uk
    Householder applications granted90.3 %1 July 2025 - 30 June 2026assets.publishing.service.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 Haringey
    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

    Haringey's constraints and housing in numbers

    The borough names 33 conservation areas, records 25 Article 4 directions and holds 289 listed entries. Heritage is not an afterthought here, and a basement in a conservation area is read against its street.

    Around 38.9 per cent of households live in a house or bungalow and 37.2 per cent own their home. The garden share of land is 26.6 per cent, enough to make rear digging a realistic option for terraced and semi-detached owners.

    The council granted 90.3 per cent of its 689 householder decisions in the latest year, with 94.3 per cent in time. Those are household averages, not basement outcomes, but they show a council that decides most home projects promptly once the pack is complete.

    Once the report exists, the officer checks it against the drawings. Depth, floor level, lightwell position and soil cover must agree across both, and an inconsistency is the commonest reason a pack is sent back. We read every page of the independent assessor's report against our own sections before submission, and note any difference for you to resolve with the assessor rather than the council.

    Choosing and briefing the independent assessor

    Because the assessment must come from a qualified independent assessor, the choice matters. The assessor should have no role in the design and no fee tied to the council's answer. We brief them with the survey, the proposed section and the ground investigation specification, and we leave their findings untouched.

    Where their report changes the design, say by recommending a shallower dig or a different drainage route, we redraw rather than argue. That keeps the architecture and the assessment consistent and avoids a mismatch the officer could use to refuse validation.

    What the assessment covers and who writes it

    The stages cover land stability, groundwater and surface water. The independent assessor and a structural engineer produce those; a ground investigation firm drills and reports. We draw the plans, sections and site plan the report depends on and coordinate every document so depths and levels match. Our structural calculations page explains the engineer's role.

    Approved Document C asks for a drained floor where the water table can rise to within 0.25 metres of it, and building control will test the same levels.

    Party walls, planning route and cost in Haringey

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

    Planning drawings come from our planning drawings work. For the borough's published figures see architectural drawings in Haringey; Camden and Islington border it and set rules of their own.

    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.
    Rows of brick terraced houses and gardens on a residential street
    The street around you
    Move across the plinth — the blocks rise around the pointer.

    Other services in Haringey

    Basement impact assessments nearby

    Questions

    Does every Haringey basement need an assessment?

    Yes, according to the Local Validation List: all applications for new basement development, including extensions to existing basements.

    Who must write the Haringey assessment?

    A qualified and recognised independent assessor, paid for by the applicant. We coordinate the findings with the drawings.

    Does the borough policy set a depth limit?

    It has no numeric garden percentage, depth or storey limit. It tests stability, flood risk, soil depth and trees.

    How long does a Haringey basement application take?

    The decision period only starts once the application is validated, and validation needs the assessment. Allow time for the ground investigation and the independent assessor before you submit, then for the council's own determination period.

    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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