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Bright finished basement room with a glass-balustrade staircase, high windows and a built-in desk
Photograph: Point3D Commercial Imaging Ltd.

01Westminster, London

Basement conversion drawings in Westminster

Westminster limits a basement to 50% of the garden and 1 storey below the lowest original floor, with soil above the roof. We draw the lower floor against each limit from £1,995 including VAT, so the officer can read compliance straight off the sections.

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    02The brief

    The four basement limits in Westminster's City Plan

    The basement policy of City Plan 2019-2040 (2026) sets four limits, and our sections show each as a labelled dimension. A basement should not extend beneath more than 50% of the garden land. It should not exceed 1 storey beneath the lowest original floor level, except on large sites with high accessibility for construction.

    Above the basement roof the policy asks for 1 m soil + 200 mm drainage, with a margin of undeveloped garden left around the boundary. Under the street, a basement may not encroach more than 1.8 m beneath the adjacent highway.

    Brick house being extended, with a wide new opening supported over the ground floor
    Georgian brick terrace with sash windows, arched fanlight doorways, stone steps and iron railings in London
    Photograph: Lorenc Memaga

    03The record

    Local figures for Westminster

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Basements should not extend beneath more than 50% of the garden land; where the garden is 8m or less at its longest point they may extend up to 4m from the original building.50%No periodwestminster.gov.uk, City Plan 2026, Policy 50, p.203, Policy 50 B1
    Basements should not comprise more than one storey beneath the lowest original floor level, except on large sites with high accessibility for construction.1 storeyNo periodwestminster.gov.uk, City Plan 2026, Policy 50, p.203, Policy 50 B3
    Basements must provide at least one metre of soil depth plus a 200mm drainage layer above the basement roof, and leave a margin of undeveloped garden around the site boundary.1 m soil + 200 mm drainageNo periodwestminster.gov.uk, City Plan 2026, Policy 50, p.203, Policy 50 B2 and B4
    Basements must not encroach more than 1.8m under the adjacent highway and must keep 900mm between the highway surface and the vault structure.1.8 mNo periodwestminster.gov.uk, City Plan 2026, Policy 50, p.203, Policy 50 B5
    Local planCity Plan 2019-2040 (2026)No periodwestminster.gov.uk
    Listed building entries4,015 list entries (Historic England, within the LPA boundary)No periodplanning.data.gov.uk
    Conservation areas56 named conservation areas published by the councilNo periodplanning.data.gov.uk
    Tree preservation orders685 tree preservation orders published by the councilNo periodplanning.data.gov.uk
    Domestic gardens share of land (GLUD 2005)7.9 % of land that is domestic garden (GLUD 2005)2005data.london.gov.uk
    Party Wall etc. Act 1996 s6(1), s6(2), s6(5)Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundationsNo periodlegislation.gov.uk
    Approved Document B Vol 1, para 2.16Basement storeys with habitable rooms need an escape window or external door, or a protected stair to a final exitNo periodgov.uk
    Householder: alterations/extensions to a single dwellinghouse, from 1 Apr 2026548 GBPNo periodribblevalley.gov.uk

    A blank value means the figure has not been published, not that there are none. Check your own address with the council.

    Westminster7 neighbouring councils
    Councils bordering Westminster

    04The streets

    Householder applications by street in Westminster

    Streets in Westminster with the most householder applications, and the share approved
    StreetApplicationsApproved
    Randolph Avenue1679%
    Ashworth Road1385%
    Clifton Hill1170%
    Ponsonby Place10100%
    Lancaster Mews938%
    Westbourne Park Road988%
    Carlton Hill886%
    Kilburn Lane886%
    Sutherland Place863%
    Wilton Row8100%
    Caroline Close733%
    Chester Row7100%
    Greenberry Street757%
    Hereford Road760%
    Hyde Park Gardens Mews775%

    Counts of householder applications by street; no individual applications are shown. Streets with fewer than five applications are left out.

    GLA Planning London Datahub, householder applications

    05The drawing

    A basement in sectionA, Westminster: depth and garden share: 50%. B, Westminster: excavation depth: 1 storey. C, Westminster: soil over the basement: 1 m soil + 200 mm drainage. D, Westminster: footprint: 1.8 m. E, Party wall notice for excavation: Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations. F, Escape from basement rooms: Basement storeys with habitable rooms need an escape window or external door, or a protected stair to a final exitABCDEF

    A basement in section

    A house and garden over a single-storey basement. The lettered marks show the limits the legend gives.

    A Westminster: depth and garden share
    50%
    B Westminster: excavation depth
    1 storey
    C Westminster: soil over the basement
    1 m soil + 200 mm drainage
    D Westminster: footprint
    1.8 m
    E Party wall notice for excavation
    Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations
    F Escape from basement rooms
    Basement storeys with habitable rooms need an escape window or external door, or a protected stair to a final exit
    The basement in three dimensions3D
    Scroll the page: the model turns with it.

    06The detail

    Gardens, trees and vaults

    Domestic gardens made up 7.9% of Westminster's land in an older survey, so the garden dimension is the first thing we measure. The council also publishes 685 tree preservation orders, which we check before the garden is drawn.

    The highway limit matters on terraced streets with vaults beneath the pavement, because the policy measures how far a basement reaches under the street and keeps clearance between the surface and the vault structure.

    Listed and conservation-area houses

    Westminster holds 4,015 list entries, 56 conservation areas and 10 Article 4 directions. Excavation under a listed house is structural work to listed fabric, so listed building consent drawings in Westminster runs alongside the planning drawing. A roof change on the same house is covered by mansard roof drawings in Westminster.

    Neighbours, escape and the period streets

    The Party Wall etc. Act 1996 reaches excavation: Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations. For habitable rooms below ground, Basement storeys with habitable rooms need an escape window or external door, or a protected stair to a final exit.

    For period terraces, the guides to Mayfair, Marylebone and Knightsbridge each set out the conservation areas around them. The basement conversion hub compares boroughs.

    Planning sheet for a single-storey rear extension: proposed ground floor plan and rear elevation, with the Property Architecture title block
    Sample drawing. Proposed plan and rear elevation from a planning application set, sheet 03 at 1:50.

    07The papers

    What the drawings rest on

    Rear view of brick terraced houses in London with slate roofs and chimney stacks along the shared rooflineParty wall services
    Photograph: Ben Hadfield
    Structural calculation sheet for a steel beam over a new rear opening, with the load diagram, loading table and section checks
    Sample drawing. Beam B1 over a new rear opening: loading, bending moment and section checks.

    08Correspondence

    Questions

    How deep can a basement go in Westminster?

    The policy says no more than 1 storey beneath the lowest original floor level, except on large sites with high accessibility for construction.

    How much of the garden can a Westminster basement cover?

    The policy says it should not extend beneath more than 50% of the garden land. We measure the garden first and draw the footprint to that limit.

    Does a basement in Westminster need a party wall notice?

    Often. Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations. Our party wall notice service is priced per adjoining owner.

    What do basement conversion drawings cost in Westminster?

    Our fee starts at £1,995 including VAT. The council's householder fee is £548, paid separately.

    Rows of brick terraced houses and gardens on a residential street

    7.9%

    of land that is domestic garden (GLUD 2005)

    Domestic gardens share of land (GLUD 2005), Westminster, 2005. Source: data.london.gov.uk

    Photograph: Altaf Shah

    09Further reading

    Other services in Westminster

    Basement conversion drawings nearby

    10Sources

    Sources and dates

    Licences

    Kensington street lined with brick townhouses and lit streetlamps beneath an orange dusk sky

    Send us the address of your house.

    We look up the conservation area, listing and Article 4 position, then reply with a fixed fee. A message before 3pm is answered the same working day.

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    Basement conversion drawings in Westminster