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Bright finished basement room with a glass-balustrade staircase, high windows and a built-in desk
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01Merton, London

Basement conversion drawings in Merton

Merton sets its basement limits in a dedicated SPD, and domestic gardens cover 27.2% of its land in the GLA land-use data, so the garden-take limit is the first one we check. We draw to it from £1,995 including VAT and coordinate the structural calculations behind it.

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    02The brief

    The limits in the Basement and Subterranean SPD

    Merton's Basement and subterranean SPD sets the tests. The policy says a basement must not exceed 50% of garden, leaving a usable single area of garden untouched. Where a basement lies beneath a garden, the scheme needs a sustainable drainage design with 1.0 m soil above any part of it.

    The SPD says a basement impact assessment may be needed to show the scheme does no harm, submitted with the application, and its guidance describes an outline construction method statement. We fix the garden take and the soil depth at the first design option, because the slab level and the engineer's design follow from them.

    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 Merton

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Basements must not exceed 50% of the front, rear or side garden and leave a usable single area of unaffected garden (policy DM D2(b)(iv)).50% of gardenNo periodmerton.gov.uk, Merton Basement and Subterranean SPD 2017, para 3.4, PDF p.5 (DM D2(b)(iv))
    Basements beneath a garden need a sustainable drainage scheme with 1.0 m of permeable soil depth above any part of the basement (DM D2(b)(v)).1.0 m soilNo periodmerton.gov.uk, Merton Basement and Subterranean SPD 2017, para 3.4, PDF p.5 (DM D2(b)(v))
    Supplementary planning documentBasement and subterranean SPD2017merton.gov.uk
    Domestic gardens share of land (GLUD 2005)27.2 % of land that is domestic garden (GLUD 2005)2005data.london.gov.uk
    Listed building entries243 list entries (Historic England, within the LPA boundary)No periodplanning.data.gov.uk
    Conservation areas28 named conservation areas published by the councilNo periodplanning.data.gov.uk
    Householder applications granted92.9 %1 July 2025 - 30 June 2026assets.publishing.service.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.

    Merton5 neighbouring councils
    Councils bordering Merton

    04The streets

    Householder applications by street in Merton

    Streets in Merton with the most householder applications, and the share approved
    StreetApplicationsApproved
    South Park Road2696%
    Lower Morden Lane2584%
    Coombe Lane2383%
    Pepys Road2377%
    Palmerston Road21100%
    Dorset Road2072%
    Marryat Road2094%
    Mostyn Road2089%
    Springfield Avenue1995%
    Vineyard Hill Road19100%
    Claremont Avenue1888%
    Queen's Road18100%
    Faraday Road1782%
    Gladstone Road1760%
    Stroud Road1794%

    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, Merton: depth and garden share: 50% of garden. B, Merton: excavation depth: 1.0 m soil. C, 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. D, Escape from basement rooms: Basement storeys with habitable rooms need an escape window or external door, or a protected stair to a final exitABCD

    A basement in section

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

    A Merton: depth and garden share
    50% of garden
    B Merton: excavation depth
    1.0 m soil
    C 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
    D 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

    Why a period house changes the sums

    A basement under a listed house needs consent as well as permission, and Historic England records 243 list entries in the borough. 28 conservation areas add a further layer of control. The consent route is set out in listed building consent drawings in Merton.

    Merton also has an Article 4 direction on HMO conversions (C3 to C4), which concerns change of use, so it does not by itself restrict digging down.

    Drainage, soil depth and the neighbour's boundary

    The SPD's single area of unaffected garden and its soil depth over the slab both shape where the pit can go, and that same line decides how close the dig comes to next door. 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. A dispute arises if the adjoining owner does not consent within 14 days of the notice.

    The drainage scheme for the garden above the slab and the escape route below it are drawn together, so the stair, the window and the soil layer do not compete for depth. Basement storeys with habitable rooms need an escape window or external door, or a protected stair to a final exit. All dwellings: fire detection and alarm system minimum Grade D2 Category LD3 (BS 5839-6), mains-operated smoke alarms to BS EN 14604.

    Householder decisions and the fee table

    Merton decided 759 householder applications in the latest return, 92.9% granted. A basement is one kind of householder work among many, so read the figure as a general guide to how the council treats home alterations. Merton takes £548 to receive a householder application, on top of our fixed fee.

    The London Plan leaves large basements to the boroughs where they are a local issue, so the borough's own SPD is where the limits are set.

    Roofs and the wider route

    If the same house needs a new roof storey, the roof route is in mansard roof drawings in Merton. The general route for lower floors is on the basement conversion drawings hub, and the Wimbledon conservation areas are described in architectural drawings in Wimbledon.

    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 much of my garden can a Merton basement take?

    The SPD's limit reads 50% of garden, and a usable single area of garden must remain. We measure your garden at the survey so the plan shows the figure against the limit.

    Do I need a basement impact assessment in Merton?

    Often. The SPD says one may be needed to show the scheme does no harm, and that it goes in with the application. Its guidance also sets out an outline construction method statement. We coordinate the structural engineer who prepares it.

    What does a neighbour have to agree to?

    A party wall notice is needed when you dig near their foundations, and A dispute arises if the adjoining owner does not consent within 14 days of the notice. Our section drawings show the foundation levels on both sides of the boundary, so the notice and any surveyor start from the same levels.

    Rows of brick terraced houses and gardens on a residential street

    92.9%

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

    Photograph: Altaf Shah

    09Further reading

    Other services in Merton

    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 Merton: SPD limits