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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.

01Bexley, London

Basement drawings for Bexley houses: flood zones, sewers and the valve on the drain

Bexley asks two things of a basement. The Local Plan says basements are not permitted in Flood Zones 2 or 3, and every scheme that does go ahead must meet one more condition: non-return valve required. We check the flood zone before quoting from £1,995 including VAT, then draw the drain as carefully as the room.

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    02The brief

    Two clauses that decide a Bexley basement

    The first clause comes from the policy on flood risk management and works as a bar: basements are not permitted in Flood Zones 2 or 3. The second applies in every zone and starts from the assumption that the sewer can surcharge, so each basement carries protection against backflow.

    The Bexley Local Plan was adopted in 2023. The council's design guidance, the Design Guide SPD Part 2: Building Alterations and Extensions, is the general guide, and we hold no basement rule from it. The two clauses are therefore the local rules to draw to.

    Georgian brick terrace with sash windows, arched fanlight doorways, stone steps and iron railings in London
    Rear view of brick terraced houses in London with slate roofs and chimney stacks along the shared roofline
    Photograph: Ben Hadfield

    03The record

    Local figures for Bexley

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Basements are not permitted in Flood Zones 2 or 3.not permitted in Flood Zones 2 or 3No periodbexley.gov.uk, Bexley Local Plan (adopted April 2023), Policy DP32 Flood risk management, part 7
    All basement schemes should include anti-backflow protection such as a non-return valve, assuming sewer surcharge.non-return valve requiredNo periodbexley.gov.uk, Bexley Local Plan (adopted April 2023), Policy DP32 part 9
    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
    CIL Regulations 2010 regs 42A-42BResidential extensions and annexes can claim exemption (claim before commencement)No periodlegislation.gov.uk
    Local planBexley Local PlanNo periodbexley.gov.uk
    Supplementary planning documentDesign Guide SPD Part 2: Building Alterations and Extensions2026bexley.gov.uk
    Domestic gardens share of land (GLUD 2005)25.1 % of land that is domestic garden (GLUD 2005)2005data.london.gov.uk
    Listed building entries114 list entries (Historic England, within the LPA boundary)No periodplanning.data.gov.uk
    Conservation areas23 named conservation areas published by the councilNo periodplanning.data.gov.uk
    Households living in a house75.3 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Householder applications granted94.6 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk

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

    Bexley7 neighbouring councils
    Councils bordering Bexley

    04The streets

    Householder applications by street in Bexley

    Streets in Bexley with the most householder applications, and the share approved
    StreetApplicationsApproved
    Rydal Drive3688%
    Danson Road3578%
    Glenhurst Avenue3491%
    Westwood Lane3494%
    Wren Road3389%
    Harland Avenue3297%
    Halfway Street3167%
    Northumberland Avenue3197%
    Okehampton Crescent3090%
    Upton Road2679%
    Bellegrove Road2591%
    Latham Road25100%
    Mayplace Road East2584%
    Walton Road25100%
    Wansunt Road2596%

    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, 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. B, Escape from basement rooms: Basement storeys with habitable rooms need an escape window or external door, or a protected stair to a final exitAB

    A basement in section

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

    A 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
    B 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

    Drawing the drain, not just the room

    Domestic gardens cover 25.1% of Bexley in the GLA's Generalised Land Use Database, and a rear basement usually sits under or beside one. We put the drain run, the position of the non-return valve and any pump on the proposed plan and a long section, because the sewer connection is part of the case an officer reads.

    A basement bedroom or study must also have a way out. Basement storeys with habitable rooms need an escape window or external door, or a protected stair to a final exit.

    Heritage and listed houses

    Bexley holds 114 list entries and 23 conservation areas, and a basement under a listed house needs listed building consent as well as planning permission.

    The consent application is set out in listed building consent drawings in Bexley, which is worth reading before you commission a survey.

    Family houses, the levy and the roof above

    Houses and bungalows are home to 75.3% of Bexley households, and the council grants 94.6% of its householder applications. With that many family houses, the levy question comes up often: Residential extensions and annexes can claim exemption (claim before commencement).

    A basement project sometimes grows to include the roof, which is a separate application covered by mansard roof drawings in Bexley. The basement conversion hub compares how councils elsewhere write their limits.

    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

    Brick house being extended, with a wide new opening supported over the ground floorStructural calculations
    Photograph: Brett Jordan
    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

    Which Bexley addresses are ruled out for a basement?

    The Local Plan position is that basements are not permitted in Flood Zones 2 or 3. The Environment Agency map shows the zone for an individual address, and our planning check starts there.

    What is a non-return valve for?

    It stops sewage flowing back into a basement when the sewer is overloaded. Bexley expects protection against backflow on every basement scheme, and we show the valve on the drainage drawing.

    Do I pay the Community Infrastructure Levy on a Bexley basement?

    The national rule for residential extensions is: Residential extensions and annexes can claim exemption (claim before commencement). We tell you at the quote stage whether the form is relevant to your scheme.

    Rows of brick terraced houses and gardens on a residential street

    94.6%

    Householder applications granted, Bexley, 1 July 2025 - 30 June 2026. Source: assets.publishing.service.gov.uk

    Photograph: Altaf Shah

    09Further reading

    Other services in Bexley

    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 Bexley