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Greenwich, London

Basement impact assessment in Greenwich

Royal Greenwich publishes no basement document with depth or garden limits that we can cite, so a basement impact assessment here turns on heritage and ground evidence. The borough holds a large listed stock, and we read that first. 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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    Heritage drives a basement impact assessment in Greenwich

    Our research found no Greenwich policy that sets a maximum basement depth, a garden percentage or a named trigger for the assessment, so we do not invent one. What the borough does have is heritage on a scale that dominates dig-down projects. The dataset records 540 listed building entries, of which 28 are Grade I, across 23 conservation areas, with 22 entries on the Heritage at Risk Register.

    Why does that matter underground? Old brick terraces and listed houses sit on shallow foundations that can move if the ground beside them is excavated. A conservation officer reading your application will want to know what the digging does to the house, what the lightwell does to the front, and what a new floor does to the neighbour's party wall. The assessment is where that evidence lives.

    The London Plan asks boroughs to control large basements where harm is likely, and a council without a bespoke formula judges each scheme on that evidence. We therefore build the report around heritage and structure first, groundwater second, and keep the section drawings in step.

    Rows of brick terraced houses and gardens on a residential street

    Local figures for Greenwich

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Listed building entries540 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Grade I listed entries28 list entries—planning.data.gov.uk
    Conservation areas23 named conservation areas published by the council—planning.data.gov.uk
    Heritage at Risk entries22 Heritage at Risk Register entries within the LPA boundary (Historic England)—planning.data.gov.uk
    Households living in a house48.4 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Householder applications granted77.1 %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
    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 Greenwich
    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

    Greenwich housing and decisions in numbers

    Only 48.4 per cent of Greenwich households live in a house or bungalow, and 41.1 per cent own their home, which means basement demand is concentrated on the houses that do exist, often in terraces. Domestic gardens account for 23.2 per cent of the borough's land.

    On decisions, the borough dealt with 624 householder applications in the latest year and granted 77.1 per cent, though 94.2 per cent were decided in time. A lower grant rate is not a basement forecast, but it is a reason to submit a complete pack the first time, with the heritage, structural and drainage evidence already answering the questions a case officer would otherwise raise.

    The dataset records 0 per cent Green Belt in the borough, and we still confirm designations for each plot.

    Protecting the existing house during the dig

    In a listed or conservation terrace the biggest worry is movement. The usual answer is underpinning in short sequential bays, with monitoring points fixed to the walls before work begins and read at set intervals. The structural engineer specifies that method, and the assessment records it so the council and the neighbours can see the house will be watched while the ground is opened.

    Neighbours often ask for a condition survey of their own wall before the dig, and the Party Wall etc. Act 1996 provides for it through a schedule of condition. We prepare the drawings for the notice, so a record of the walls as they stand before work is part of the pack from the start.

    Who writes the assessment and what it covers

    A ground investigation firm drills the boreholes and reports on soil and groundwater, and a structural engineer designs the retaining walls and slab. We coordinate their findings with the drawings, check the plans and sections the report cites and make sure heights and depths agree. Our structural calculations page explains the engineer's part.

    Approved Document C asks that a floor is drained where the water table can rise to within 0.25 metres of it, and Approved Document A requires that ground movement does not impair stability. Both bear directly on a basement beside old foundations.

    Party walls, planning route and cost in Greenwich

    A terrace means shared walls, so the Party Wall etc. Act 1996 is rarely optional. A notice is needed for excavation within 3 metres of an adjoining building and deeper than its foundations, and within 6 metres on the 45-degree test. Our party wall notices service prepares the drawings.

    The plans, sections and site plan come from our planning drawings work. For the borough's published figures see architectural drawings in Greenwich, and note that Lewisham and Bexley adjoin it with their own rules.

    The service is unpriced because scope depends on ground and heritage. 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 Greenwich

    Basement impact assessments nearby

    Questions

    Does Greenwich have a basement policy with limits?

    We found no published basement document with depth or garden limits. The council weighs structure, heritage, groundwater and neighbours on the evidence supplied.

    Does a listed building stop a basement?

    Not automatically, but it adds a listed building consent question and a harder structural one. Greenwich holds 540 listed entries, so we check your property's status first.

    Is a party wall notice needed for a terrace basement?

    Usually, if you dig within 3 metres of the neighbour and below their foundations. We prepare the drawings for it.

    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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