A site-specific flood risk assessment (FRA) — the report a planning application needs once a site sits in, or is near, a mapped flood risk area — typically costs £450–£900 for a straightforward desk-based report on a householder extension or single dwelling in 2026, rising to £650–£1,800 for a minor residential scheme of up to nine dwellings in Flood Zone 2 or 3a. Add a sustainable drainage strategy, a scheme of ten homes or more, or hydraulic modelling and the Exception Test, and the fee moves into £1,850–£8,000+ territory.
None of those figures matters first, though. What decides whether you need an FRA at all, and which tier of it, is the site's flood zone, its size, and — since 17 August 2026 — a brand new National Planning Policy Framework that rewrote the flood risk chapter from scratch. Commission the wrong tier, or work from the superseded rules, and the fee you've paid may not answer the question your planning authority actually asks.
I'm a building surveyor, not a flood risk consultant — this isn't a report I write myself, and where a site genuinely needs one, that's a job for a specialist with proper hydrology and drainage modelling behind them. What follows is 2026 pricing checked against current UK flood consultancies' published fees, what actually triggers the requirement under the new Framework, and why a fair slice of my own Kent, Sussex and Surrey patch sits closer to this question than most homeowners realise.
The short answer
Figures below were checked on 19 September 2026 against several UK flood risk consultancies' published fee schedules and cost guides, cross-referenced against each other. As with most reports in this series, a fixed quote against a clearly stated brief is the norm; what varies most is which tier of assessment the site actually needs.
| Site / project type | Typical cost (2026) | What's included |
|---|---|---|
| Householder extension, Flood Zone 2 or 3 (desk-based) | £450–£900 | Desk study of EA and council flood data, no site-specific modelling |
| Minor development, up to 9 dwellings, Zone 2 or 3a | £650–£1,800 | Site visit, climate change allowance, safe access and egress review |
| Scheme needing a sustainable drainage (SuDS) strategy | £1,500–£3,500 | Level 2 assessment plus a drainage design to the 2025 National Standards |
| Major development, Zone 3a/3b, or Sequential/Exception Test with modelling | £3,000–£8,000+ | 1D/2D hydraulic modelling, breach or overtopping assessment |
Two things push a quote to the top of any band. One is site-specific hydraulic modelling, because buying and running Environment Agency model data isn't free to the consultant doing it. The other is a resubmission after a planning officer or the EA's own consultation response asks for more detail — common enough on a first attempt at a Zone 3 site to price in from the outset, not treat as a surprise.
What drives the price
Flood zone. Zone 1 (low probability) rarely needs a full FRA unless the site is large or otherwise flagged; Zone 2 (medium) and Zone 3a (high) almost always do; Zone 3b, the functional floodplain, needs the most thorough treatment of all.
Site size and dwelling count. A single extension is priced very differently from a 12-plot scheme, largely because of how much modelling and drainage design the larger site has to demonstrate.
Hydraulic modelling. Once a desk study of existing EA mapping isn't detailed enough — usually because the site is in Zone 3, or flood depth and velocity genuinely matter to the design — site-specific 1D or 2D modelling adds several thousand pounds on its own.
The Sequential and Exception Tests. Usually written up by the same consultant alongside the FRA rather than commissioned separately, but a genuine search of alternative sites for the Sequential Test, or the sustainability-benefit case the Exception Test needs, adds real hours on top of a basic assessment.
Revisions. A first FRA coming back with planning authority or EA comments to address is common above a simple extension; most consultants price a round of revisions into the fee rather than charging separately — worth confirming before you instruct anyone.
Do you actually need one?
The date matters more here than almost anywhere else in this series. The National Planning Policy Framework published on 17 August 2026 replaced the December 2024 version and rewrote flood risk policy from the ground up: the old scattered paragraphs are gone, replaced by a dedicated chapter of nine coded policies, with the flood zone definitions and vulnerability classifications moved into the Framework itself as a new annex rather than a separate technical guidance document — meaning those tables now carry full national planning policy weight. The new Framework applies to every decision made from 17 August 2026 onward, including applications submitted under the superseded rules, so a scheme already in the system when the change landed can find itself assessed against a different set of tests partway through.
Under the current rules, an FRA is always required in Flood Zone 2, 3a and 3b. In Flood Zone 1, it's required where the site is 1 hectare or larger, where strategic assessment or the Environment Agency's Flood Map for Planning shows the site at risk, where there's a known critical drainage problem, or where the development would change the vulnerability classification of the site's use. That last trigger used to bite only where a "more vulnerable" use was proposed; the qualifier has been dropped, genuinely widening the number of Zone 1 sites that now need an assessment they might previously have avoided.
Not every flood-zone project needs a paid consultant, though. A minor extension — a household or non-domestic extension of no more than 250 square metres — can normally be assessed against the Environment Agency's own published standing advice rather than a bespoke report, even in Flood Zone 2 or 3, because the risk from a modest extension is well enough understood not to need site-specific modelling every time. Worth checking with the planning case officer first whether the area has a recognised problem with cumulative flood risk from repeated nearby minor extensions; if it has, they may ask for more than the standing advice covers. For most single extensions, though, this route removes the FRA fee from the job entirely.
Where a full assessment is needed, an October 2025 practice guidance update is worth knowing too: it clarified that the Sequential Test isn't required where the FRA itself demonstrates that no new development, or its access and egress, would sit in an at-risk area — useful where buildings can genuinely be designed around the flood-prone part of a plot. And where a site is already allocated for development in the local plan, the Exception Test shouldn't be repeated at application stage unless the flood risk assumptions or mitigation have changed since allocation — a saving worth raising with a consultant who quotes for it as routine.
Kent, Sussex and Surrey: closer to this than you'd think
This isn't just a coastal or big-city problem in the South East. Hartfield sits in the Sussex Ouse catchment, and low-lying land and roads near the rivers around Hartfield, Forest Row, Ashurst and Penshurst are recognised as flood-prone by the county's own flood management planning — the same catchment where the Ouse overtopped badly at Lewes and Uckfield in 2000, an event that still shapes local policy. Further into Kent, the Medway and its tributaries converge around Tonbridge, Yalding and Maidstone in the county's worst river-flooding areas, while Thanet and Romney Marsh sit behind sea and tidal defences of their own.
Surface water flooding is also assessed on its own terms: areas of high or medium surface water risk are treated as broadly equivalent to Flood Zone 3 for planning purposes, low risk as equivalent to Zone 2, even where a site sits in Zone 1 for river and sea purposes. An ordinary-looking plot well away from any river can still trigger an FRA on surface water grounds alone, particularly on the clay-heavy ground common across the Weald, where water sits on the surface rather than draining away.
What I'd watch for in a quote
- Confirm which tier is being quoted — a desk-based Level 1 assessment and a modelled Level 3 assessment are very different jobs, and the two get conflated on the phone more often than they should.
- Check the quote is against the August 2026 NPPF, not the superseded December 2024 version — a consultant working from out-of-date policy can miss a trigger that now applies.
- Ask whether the Sequential and Exception Tests are included in the headline fee, and whether the Exception Test can be skipped because the site is already allocated.
- Ask whether the drainage design follows the 2025 National Standards for Sustainable Drainage Systems, now expected on all development, not just major schemes.
- Get a fixed fee against a written brief, including what a round of revisions after planning authority comments costs.
Questions I get asked
How much does a flood risk assessment cost in 2026? A desk-based assessment for a householder extension or single dwelling in Flood Zone 2 or 3 typically costs £450–£900. A minor residential scheme of up to nine dwellings in Flood Zone 2 or 3a runs £650–£1,800. Add a sustainable drainage strategy and it's closer to £1,500–£3,500, and a major development, a Flood Zone 3b site, or one needing hydraulic modelling or the Exception Test can reach £3,000–£8,000 or more.
Do I need a flood risk assessment for a house extension? Not always, even in Flood Zone 2 or 3. A minor extension of no more than 250 square metres can usually be assessed against the Environment Agency's published standing advice rather than a bespoke paid report, provided the planning authority hasn't flagged cumulative flood risk from multiple nearby minor extensions. Check with the case officer before assuming you need to pay a consultant.
What changed for flood risk in the August 2026 NPPF? The Framework published on 17 August 2026 rewrote flood risk policy into a dedicated chapter of nine coded policies and moved the flood zone and vulnerability tables into the Framework itself, giving them full policy weight. The old Flood Zone 1 requirement for a "more vulnerable use" has been dropped, widening how many Zone 1 sites now need an FRA. The new rules apply to every decision from 17 August 2026 onward, including applications submitted under the previous version.
Does a flood risk assessment tell me if a house I'm buying has ever flooded? No. An FRA is a forward-looking planning document prepared to support new development, not a check on an existing building's history. If you're buying and want to know how a property would cope, or whether it shows evidence of past water ingress, that's a question for a proper building or HomeBuyer survey instead.
A flood risk assessment is a planning document, not a verdict on a house you already own or are buying — it says nothing about how an existing building has fared over the years. If you're selling and want that climate-change risk picture in front of a buyer before their own surveyor raises it, that's part of what my Home Insight Survey covers; if you're buying, my building survey work will flag anything on site pointing to a flooding or drainage history worth asking harder questions about. The site levels an FRA relies on, incidentally, come from a proper topographical survey. Call 07946 618203 or get in touch for an independent read on a property before you commit.
Small print. This guide is general information, not advice on a specific site or application, and it doesn’t replace a proper flood risk assessment or your planning authority's own requirements. Prices were researched and correct to the best of my knowledge on 19 September 2026; costs move and vary by region, consultant and site complexity. Always get at least three written quotes, and confirm any quote is priced against the current National Planning Policy Framework.