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Brick cottage with a tiled roof, chimneys and a front dormer window

Planning

Flood risk assessments for London homes

If your site lies in a flood zone, the council will not register a planning application without a flood risk assessment. We arrange a minor householder assessment through an accredited partner and coordinate it with your drawings, from £379. The partner signs the assessment; we make sure it fits the scheme.

From £379, no VAT to add

  • MCIAT chartered
  • £2m PI insured
  • LABC Partnered
  • Fixed fees, no VAT to add

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We use it to check conservation areas and constraints.
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    The fixed fee for flood risk assessments

    Fixed fee
    from £379
    Total you pay
    from £379
    Council fee
    paid to the council separately

    No VAT to add. The fee is fixed in writing after a free constraints check of your address.

    What you get

    • A check of your flood zone and data sources
    • A minor householder flood risk assessment through an accredited partner
    • Floor levels and resilience measures coordinated with your drawings
    • Help requesting the Environment Agency's site data
    • The report ready to submit with your planning application
    • Answers to the council's questions about it
    Request your fixed quoteCall 020 7131 9703
    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 flood risk 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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    When one is required

    The government's guidance names three cases. The first applies to many riverside London streets: "Development in Flood Zones 2 or 3, including minor development and changes of use." The second is about large sites, where a site of 1 in the low-risk zone also needs one.

    Skipping it is not an option the council will tolerate: "The local planning authority may refuse your application if you do not include a flood risk assessment or if it is not satisfactory." That means an application held up at validation or refused for a document that could have been commissioned in advance.

    Check your zone on the Environment Agency's flood map for planning. Our planning constraints report does that for you, together with the other designations.

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

    What a householder assessment covers

    For a modest scheme the assessment is short. It identifies the flood zone, says where the water could come from, explains how the extension is protected and shows that it does not make flooding worse for anyone else.

    Government guidance asks for an honest forward look: "The design flood estimate must include an appropriate allowance for climate change." The assessment uses the Environment Agency's data, and for detailed levels the agency produces a site map. It says it will send that "20" working days after a request, so ask early.

    Minor extensions and floor levels

    The Environment Agency has standing advice for small schemes. The guidance defines a minor extension as a household or non-domestic extension with a floor space of no more than 250.

    The standing advice recommends floor levels "600" millimetres above the estimated flood level, and flood resistance measures where the floor cannot be raised. That affects the drawings: a floor level, a step at the threshold, a raised damp-proof course. We design these with the assessor so the section drawings and the report say the same thing.

    Why it goes through a partner

    A flood risk assessment is a technical document and needs a specialist's name on it. We use accredited partners and manage the exchange, so you deal with one practice and one timetable.

    That is why this service is priced as an arranged report, not a drawing. You will still see the partner's work before it is submitted.

    Putting it into your application

    The assessment goes in with your planning drawings and is referenced on the plans where it affects them. If your site is also in a conservation area, you may need a design and access statement in the same pack.

    The council and the Environment Agency decide how they respond. We cannot promise their view, and we say so when we quote.

    The national rules in figures

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Flood risk assessment for planning applications: when one is needed in Flood Zones 2 and 3Development in Flood Zones 2 or 3, including minor development and changes of use—gov.uk
    Flood risk assessment for planning applications: size threshold in Flood Zone 11 hectare or more—gov.uk
    Flood risk assessment for planning applications: what the council may doThe local planning authority may refuse your application if you do not include a flood risk assessment or if it is not satisfactory—gov.uk
    Flood risk assessment for planning applications: climate changeThe design flood estimate must include an appropriate allowance for climate change—gov.uk
    Flood risk assessment for planning applications: what counts as a minor extension250 square metres or less of floor space—gov.uk
    Flood risk assessment standing advice: recommended floor level above the estimated flood level600 millimetres—gov.uk
    Flood risk assessment for planning applications: Environment Agency detailed flood map (Product 4) turnaround20 working days—gov.uk

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

    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 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.

    Questions

    How do I know if I am in a flood zone?

    Use the Environment Agency's flood map for planning with your address. If you would rather not, our constraints report does it and explains the result.

    Does a flood risk assessment stop my extension?

    Not by itself. It shows how the extension is protected. A good result supports the application; the council still decides.

    Is surface water flooding the same thing?

    It is a separate source, and the assessment should consider all sources. We ask the assessor to cover surface water and sewer flooding where they apply.

    Can I get the assessment after submitting?

    The council can refuse to register an application that needs one, so it is better commissioned first.

    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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