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Kensington and Chelsea, London

Basement impact assessment in Kensington and Chelsea

A basement impact assessment in Kensington and Chelsea starts from hard limits: one storey, a cap on garden coverage and a metre of soil above the roof slab. Schemes that pass are documented in detail. We test your house against those limits 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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    Brick cottage with a tiled roof, chimneys and a front dormer window

    The Kensington and Chelsea basement rules

    The borough's basement test sits in its Local Plan 2024 (New Local Plan Review) and in the Basements SPD. The core clause reads: 50% garden; 1 storey; 1 m soil. Large sites can be treated differently, but a typical terrace or mews house cannot.

    A second group of clauses governs what the basement does once built: Pumped device; SuDS retained. In plain terms there is no second basement floor beneath an existing one, no excavation under a listed building, and sewer flooding is dealt with by a pumped device rather than a simple valve.

    The validation list adds a paperwork rule: CMS for every basement. That means the construction method has to be thought through before the application is lodged, not left to a later condition.

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

    Local figures for Kensington and Chelsea

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Policy CD11 A, B and J: basements must not exceed 50% of each garden or open part of the site (unaffected garden in a single area), must not exceed one storey, and must include at least 1 m of soil above any part of the basement beneath a garden. Exceptions only on large sites. Measured as GEA; a 'single storey' is generally 3 to 4 m floor to ceiling.50% garden; 1 storey; 1 m soil—rbkc.gov.uk, RBKC Local Plan 2024 (adopted July 2024), Policy CD11 A, B, J (printed pp.251-252); paras 6.94-6.95 (p.254), 6.108 (p.258)
    CD11 C and F: no further basement floors where a basement exists by permission or PD; no excavation under a listed building (including vaults). CD11 I: a SuDS must be included and retained. CD11 N: basements must be protected from sewer flooding by a suitable pumped device; a non-return valve alone is not acceptable.Pumped device; SuDS retained—rbkc.gov.uk, RBKC Local Plan 2024 (adopted July 2024), Policy CD11 C, F, I, N (printed pp.252-253); para 6.111 (p.258)
    Validation list: a Construction Method Statement is required for all developments with new or enlarged basements; a Construction Traffic Management Plan for basements and majors (CTMP pro-forma); noise survey for basements; Flood Risk Assessment for sites of 1 ha or more in FZ1, flood zones 2 and 3 and Critical Drainage Areas.CMS for every basement—rbkc.gov.uk, RBKC Submission Requirements for Planning Applications (10 March 2023), pp.12-13 (table); Notes 14 and 15 (pp.31-32); Note 8 (p.25)
    Conservation areas39 named conservation areas published by the council—planning.data.gov.uk
    Article 4 directions84 Article 4 directions published by the council—planning.data.gov.uk
    Listed building entries1,350 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Domestic gardens share of land (GLUD 2005)17.5 % of land that is domestic garden (GLUD 2005)2005data.london.gov.uk
    Householder applications granted93.7 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder applications decided in time91.9 % decided within 8 weeks or an agreed extended period1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    RBKC Basements SPD (April 2016), Construction Method Statement item on ground movement (PDF p.31)Limit predicted damage to CIRIA C580 Table 2.5 Category 1 ('very slight', up to 1 mm) and never more than Category 2 ('slight', up to 5 mm)—rbkc.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 Kensington and Chelsea
    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

    What the numbers mean for a Kensington and Chelsea house

    Gardens are the limiting factor. Domestic gardens make up only 17.5 per cent of the borough in the national land-use database, and only 17 per cent of households live in a house, so many basement briefs concern a flat or a mews property with a courtyard rather than a deep rear garden.

    A garden percentage can be measured two ways, and councils read it strictly. We calculate it on the gross external area of the excavation, not the room you will actually use, because that is the measure the borough applies. A scheme that looks comfortable on the plan can be over the line once the lightwell and the stair are counted.

    Because the borough reads a single storey as a set floor-to-ceiling range, we set the structural depth, the slab and the finishes inside that envelope before the design is fixed.

    Heritage, listing and Article 4 in the borough

    Kensington and Chelsea combines very high heritage density with active policy. It has 39 conservation areas, 84 Article 4 directions and 1,350 listed building entries, including 18 at Grade I and 16 registered parks and gardens within its boundary.

    The Article 4 directions matter for basements because they can bring changes to the front of a house, which a lightwell often involves, under planning control. A lightwell on a listed or Article 4 frontage is treated as a heritage application with a basement attached, so the heritage statement and the assessment have to be consistent.

    How the borough decides householder schemes

    In its latest published year the council decided 2,292 planning applications. It granted 93.7 per cent of householder applications and 93.2 per cent of minor ones, but only 91.9 per cent of householder cases were decided within the statutory period or an agreed extension. A thorough, well-organised submission is the best protection against a long wait.

    Our planning drawings in Kensington and Chelsea page covers the main set. Typical homes here are valued at an average of £1,232,640, which is why owners accept the cost of doing a basement properly.

    Party wall and engineering duties for a Kensington and Chelsea basement

    A basement beside a neighbour needs a notice under the Party Wall etc. Act 1996 when the dig is within 3 metres of an adjoining building and deeper than its foundations, or within 6 metres on the diagonal test. Our party wall notices service prepares the drawings.

    The engineer designs the retaining walls and the council's damage test. The borough's approach limits predicted wall damage to the lowest categories: Limit predicted damage to CIRIA C580 Table 2.5 Category 1 ('very slight', up to 1 mm) and never more than Category 2 ('slight', up to 5 mm). We coordinate that with the drawings and with our structural calculations in Kensington and Chelsea.

    Fixed quote, scope and what we are

    We are chartered architectural technologists (MCIAT), so we draw, coordinate and assemble the report; the engineer and the ground investigator sign their own parts. The scope varies with depth, access and soil, so after the free constraints check you receive a fixed quote and a plain note of any limit your scheme breaches.

    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 Kensington and Chelsea

    Basement impact assessments nearby

    Questions

    What are the Kensington and Chelsea basement limits?

    The council's core rule is 50% garden; 1 storey; 1 m soil. Larger sites are the only exception.

    Can I dig a second basement level in Kensington and Chelsea?

    Not where a basement already exists by permission or permitted development, and not under a listed building. The same clause group adds Pumped device; SuDS retained for sewer flooding and drainage.

    Do I need a construction method statement?

    Yes. The borough's validation list asks for one for every new or enlarged basement: CMS for every basement.

    What does a Kensington and Chelsea basement assessment cost?

    It depends on depth, access and soil. 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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