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01Specialist reports

How much does a flood risk assessment cost in London?

A flood risk assessment for a London extension costs from £435 with us, as a fixed fee with no VAT to add. It is short for a householder scheme in a flood zone and fuller for a basement, and the fee is confirmed in writing before we start.

From £435

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Our fee for flood risk assessment: from £435, no VAT to add. Covered in full, with its own guide and fee, at fixedfeeplans.co.uk.

By Property Architecture, chartered architectural technologists (MCIAT). Published . 2 min read.

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    What it costs and what it covers

    Our fee starts at £435. We check your site against the Environment Agency's flood map for planning, then write a site-specific assessment sized to the scheme: short for a householder extension, longer for a basement. It sets out floor levels, resilience measures and a safe escape route in the form the officer is looking for.

    A larger or basement scheme is confirmed in writing first, because the work scales with the risk and the depth of the dig.

    Flood risk on a planning applicationFlood risk assessment: £435; Council fee, householder planning: £548; Flood resilience works: your builder; VAT on our fee: none to add£Flood risk assessment£435£Council fee, householder planning£548£Flood resilience worksyour builder£VAT on our feenone to add
    The assessment goes in with the planning application; the council fee is separate.

    When a site needs one

    National guidance says river and sea flood risk is principally land in flood zones 2 and 3, and flood zone 1 sites that the Environment Agency has marked for critical drainage problems are caught as well. Even for minor extensions, a site-specific assessment should be provided, though a shorter and simpler one is likely to be enough.

    We look up your address first, free, and tell you whether it is in a zone before you spend anything.

    Georgian brick terrace on Bedford Square in Bloomsbury, with arched doorways, sash windows and black iron railings
    Bedford Square: a period terrace in central London, where a ground-floor or basement extension is tested for flood risk like any other.Photograph: Steve Cadman from London, U.K., CC BY-SA 2.0

    What the assessment must show

    At a minimum, the assessment has to show that the development will be safe for its users. Extensions are advised to conform to existing flood protection and to include resilience measures: raised sockets, solid floors and materials that dry out.

    For a basement the stakes are higher, since it is the bottom storey of the house. We coordinate with the structural and drainage drawings so a flood strategy and the waterproofing agree; see our basement drawings guide.

    The council's side

    The council or the Environment Agency may comment on the assessment, and a clear document makes their questions short. Our fee includes changes if either asks.

    A householder application costs the council £548 from 1 April 2026. Our flood risk assessment page lists what the document contains.

    A narrow period house on Heath Street in Hampstead with a bay window, pale green render and a small front garden
    A narrow Hampstead house: surface water, not only rivers, can be the flood question on a London street.Photograph: Images George Rex, CC BY-SA 2.0

    Ordering

    Send the address and the scheme. We check the map and confirm whether you need an assessment and what it will cost.

    From address to assessmentSend the address and scheme; Free map check; Fixed fee in writing; Assessment written; Filed with the applicationi

    Send the address and scheme

    ii

    Free map check

    iii

    Fixed fee in writing

    iv

    Assessment written

    v

    Filed with the application

    If you do not need one, we say so.

    The figures, with sources

    1. Zones 2 and 3

      River and sea flood risk applies mainly to land in these flood zones.

      Source: GOV.UK, Flood risk and coastal change, checked 25 Oct 2026

    2. Zone 1 too

      Zone 1 sites flagged by the Environment Agency for critical drainage problems fall under the same guidance.

      Source: GOV.UK, Flood risk and coastal change, checked 25 Oct 2026

    3. Minor works

      Minor extensions should still have a site-specific assessment, though a shorter one is likely to be enough.

      Source: GOV.UK, Flood risk and coastal change, checked 25 Oct 2026

    4. Safe

      The assessment must at least show the development will be safe for the people who use it.

      Source: GOV.UK, Flood risk and coastal change, checked 25 Oct 2026

    5. Resilience

      Extensions are advised to match existing flood protection and include resilience measures.

      Source: GOV.UK, Flood risk and coastal change, checked 25 Oct 2026

    6. £548

      Council fee to decide a householder planning application from 1 April 2026.

      Source: Ribble Valley Borough Council, national fee table from 1 April 2026, checked 17 Oct 2026

    Questions

    Can you tell me which flood zone my address is in?

    Give us the address and we check the Environment Agency's flood map for planning. The check is free.

    Do I need one for a basement?

    Often, and it will be fuller than for a house extension. We confirm the scope and fee in writing first.

    Will the assessment stop the project?

    It shows whether the scheme is safe and what measures it needs. It is evidence, not a decision; the council decides.

    Does it cover surface water drainage?

    Where the site is flagged for critical drainage, yes. We say what the document will cover in the quote.

    The fee for flood risk assessment

    Flood risk assessment

    from £435

    The total you pay. No VAT to add.

    Get a fixed quote from £435

    What you get

    • Your site checked against the flood map for planning
    • An assessment sized to a house or a basement
    • Floor levels, resilience and an escape route
    • A section written for the officer's tests
    • Changes made if the council or agency asks
    Rear view of brick terraced houses in London with slate roofs and chimney stacks along the shared roofline

    Zones 2 and 3

    River and sea flood risk applies mainly to land in these flood zones. Source: gov.uk

    Photograph: Ben Hadfield

    02Guides

    More guides

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    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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    Flood Risk Assessment Cost in London: From £435