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Richmond upon Thames, London

Basement impact assessment in Richmond upon Thames

Richmond upon Thames ties the need for a basement impact assessment to where you live: a basement in a throughflow or groundwater policy zone, or in an area with a high susceptibility to groundwater flooding, needs one, with a screening step first. We check your address against those maps and give a fixed quote after a free constraints check.

Fixed quote after a free constraints check

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  • £2m PI insured
  • LABC Partnered
  • Fixed fees, VAT included

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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

    When Richmond upon Thames requires an assessment

    Richmond's validation checklist, the current version, sets a map-based trigger: Zone or 25% groundwater susceptibility triggers. In the council's wording, the requirement applies to all subterranean, basement or cellar proposals in the throughflow and groundwater policy zones, and in any area with a quarter or more susceptibility to groundwater flooding.

    A screening assessment comes first. If it shows that impacts are possible, a full basement impact assessment follows from a chartered professional, such as a civil engineer, geotechnical specialist, geologist, hydrologist or hydrogeologist, with a verification form and borehole information.

    The borough's wider framework is the Richmond Local Plan 2024-2039, adopted in 2,025. Because the trigger is a map, two neighbours can have different answers. We look up your plot, not the street.

    Rows of brick terraced houses and gardens on a residential street

    Local figures for Richmond upon Thames

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Item 37 Basement Assessment: required for all subterranean/basement/cellar proposals in throughflow and groundwater policy zones, and any in areas with 25% or more susceptibility to groundwater flooding. A Screening Assessment comes first; a Basement Impact Assessment follows if impacts are possible, by a chartered professional (civil engineer, geotechnical specialist, geologist, hydrologist or hydrogeologist), with a Site and Assessment Verification Form and borehole information.Zone or 25% groundwater susceptibility triggers—richmond.gov.uk, Richmond upon Thames Local Validation Checklist for All Applications (adopted 19 February 2026, in effect 20 February 2026), item 37, p.20-21
    Conservation areas85 named conservation areas published by the council—planning.data.gov.uk
    Listed building entries819 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Grade I listed entries40 list entries—planning.data.gov.uk
    Domestic gardens share of land (GLUD 2005)19.4 % of land that is domestic garden (GLUD 2005)2005data.london.gov.uk
    Households living in a house59.8 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Householder applications granted83.3 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder applications decided in time98.3 % 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
    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 Richmond upon Thames
    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

    Rivers, gardens and houses in Richmond upon Thames

    The groundwater test is map-based, so it is worth knowing the plot. Domestic gardens cover 19.4 per cent of the land in the national land-use database, 59.8 per cent of households live in a house and 62.4 per cent own their home. Basement briefs here are typically for owners of family houses with gardens.

    Where the screening shows a risk, the borehole data and groundwater monitoring decide how the box is built. Whatever the findings lead to, whether tanking, drainage or a pumped sump, the council wants to see it in the engineering drawings, not as a promise.

    Richmond also has a house-extension SPD for the work above the basement, the House Extensions and External Alterations SPD, which governs how a rear extension that covers the new box may look.

    If your house is in a conservation area with mature trees, the arboricultural question runs alongside the groundwater one. We plot each tree and its root protection area on the site plan, so the council sees that the box and the trees were designed together.

    Richmond upon Thames heritage and a basement

    Protected places are numerous. Richmond upon Thames has 85 conservation areas, 819 listed building entries and 40 at Grade I, with 16 registered parks and gardens, 6 scheduled monuments and 2 per cent green-belt cover.

    That heritage density means a basement is rarely a stand-alone engineering question. We prepare the heritage case and the assessment together, and where trees in a conservation area are close to the footprint, we state how they will be protected.

    How Richmond upon Thames decides householder schemes

    The council decided 1,825 planning applications in its latest published year. It granted 83.3 per cent of householder applications and 75.3 per cent of minor ones, and 98.3 per cent of householder decisions were made in time. The average house price is £803,249, so owners expect a basement to be done once and done properly.

    Our planning drawings in Richmond upon Thames page covers the main set, and the structural calculations in Richmond upon Thames page explains the engineer's role.

    Party wall and water rules for a Richmond upon Thames dig

    A notice under the Party Wall etc. Act 1996 is needed for excavation within 3 metres of an adjoining building that goes deeper than its foundations, and within 6 metres on the diagonal test. Serve it at least 1 month before work. Our party wall notices service prepares the plans.

    Building Regulations apply once planning is settled. Where the water table can rise to within 0.25 metres of the lowest floor, the floor must be drained or protected.

    Cost and next step

    We are chartered architectural technologists (MCIAT). We run the screening check, commission the specialists if it is needed and assemble one consistent submission. The price depends on whether your plot falls inside a trigger zone, so after the free constraints check you receive a fixed quote.

    Where screening shows no impact, the file is short and the quote reflects that. Where it does, we explain which specialist is needed and why, so the cost of each step is clear before you commit. Tell us if the house has a cellar already, because the checklist covers cellar proposals too.

    We also check the neighbouring houses. A terrace that shares a party wall on both sides involves two notices and two sets of neighbours, and the programme has to allow for their replies.

    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 Richmond upon Thames

    Basement impact assessments nearby

    Questions

    Does every Richmond upon Thames basement need an assessment?

    No. The checklist triggers it for Zone or 25% groundwater susceptibility triggers. We look up your plot.

    What is the screening assessment?

    A first-stage check. If it shows impacts are possible, a full assessment follows from a chartered professional.

    Does heritage affect a Richmond upon Thames basement?

    Often. With 85 conservation areas and 819 listed entries, the heritage case usually goes in with the assessment.

    What does an assessment cost?

    It depends on whether your plot is in a trigger zone. You receive a fixed quote after a free constraints check.

    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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