A flood risk assessment (FRA) is a report that shows your proposed development will be safe from flooding for its lifetime and will not increase flood risk elsewhere. In England it is a core part of the planning system: for many sites, a local planning authority cannot lawfully grant permission without one, and a missing or weak FRA is one of the most common reasons small applications are refused or delayed.
This guide explains, in plain terms, what a flood risk assessment actually is, why planning approval requires one, when you need one, and what a competent FRA must contain. If you are a homeowner, self-builder or architect trying to work out whether your project needs an FRA, start here.
What is a flood risk assessment?
A flood risk assessment is a site-specific study of how flooding could affect a development — and how the development could affect flooding on neighbouring land. It considers all sources of flooding, not just rivers and the sea: surface water (rainfall that cannot drain away), groundwater, sewers and any nearby ordinary watercourses.
A good FRA does four things. It screens the site against the Environment Agency flood maps to establish its flood zone. It assesses the actual risk to the proposed use, taking climate change into account. It sets out mitigation — finished floor levels, flood-resistant and flood-resilient construction, and a safe means of escape. And it demonstrates the development will not make flooding worse elsewhere, usually through a sustainable drainage (SuDS) strategy that controls how quickly rainwater leaves the site.
Why is a flood risk assessment required for planning approval?
The requirement flows from national planning policy. The National Planning Policy Framework (NPPF) directs development away from areas at highest flood risk, and where development in a flood-risk area is unavoidable, it must be made safe without increasing risk elsewhere. The detail sits in the government's Planning Practice Guidance (PPG) on flood risk, which was last updated in May 2026.
Two policy tests sit behind the FRA:
- The Sequential Test steers development towards land at the lowest probability of flooding. Since the September 2025 PPG update, it must consider all flood sources, including surface water with climate change.
- The Exception Test applies where development in a higher-risk zone is still necessary; it requires the scheme to deliver wider benefits and to be safe for its lifetime.
Your FRA is the evidence that satisfies these tests. Without it, a planning officer has no basis on which to conclude the development is safe — so the application either stalls or is refused. For how the underlying flood maps have just changed, see our explainer on the 2026 Flood Map for Planning update.
When do you need a flood risk assessment?
You will generally need an FRA to support a planning application in England if any of the following apply:
- the site lies in Flood Zone 2 or Flood Zone 3 on the Environment Agency flood map;
- the site is 1 hectare or larger, even in Flood Zone 1;
- the site is in an area with critical drainage problems or known surface water flood risk;
- the development could increase flood risk elsewhere — for example by adding large areas of hard surfacing; or
- you are changing the use of a building to a more vulnerable class (for instance creating a dwelling).
The quickest first step is to check your flood zone on the Environment Agency flood map for planning. If in doubt, ask before you design — retrofitting flood mitigation after a refusal is far more expensive than building it in from the start.
Understanding the flood zones
| Flood zone | Annual probability (rivers/sea) | What it usually means |
|---|---|---|
| Zone 1 | Less than 0.1% | Low risk — FRA needed if the site is 1 ha+ or has other flood sources |
| Zone 2 | 0.1% to 1% (rivers) | Medium risk — site-specific FRA required |
| Zone 3 | 1% or greater (rivers) | High risk — FRA plus Sequential/Exception Test scrutiny |
Note that these zones describe river and sea flooding only. Surface water risk is mapped separately — and, as of the May 2026 update, in far greater detail — which is why a site in Zone 1 can still need an FRA.
What a good flood risk assessment contains
- Flood zone screening against current Environment Agency data.
- Assessment of all flood sources — river, sea, surface water, groundwater and sewers.
- Climate change allowances applied to the design event.
- Finished floor levels set above the modelled flood level where required.
- Flood resistance and resilience measures, in line with Environment Agency standing advice.
- A drainage strategy using SuDS to CIRIA C753, controlling surface water runoff so the development does not worsen flooding downstream.
A report that simply states "the site is at low risk" without this evidence will not satisfy most planning authorities.
How Fortress Associates can help
Our flood risk assessment service produces a site-specific FRA for English planning applications using live Environment Agency data. The report is free, follows the Environment Agency FRA template (March 2025), screens all flood sources for the Sequential Test, and includes a SuDS drainage strategy to CIRIA C753. Whether you are planning a householder extension, a new dwelling or a small-scale scheme, contact us to get started — or see the full range of what we offer on our services page.
Sources & further reading
Need help with a UK planning project?
Fixed-fee daylight reports and Building Regulations drawings — delivered in 4–5 working days. No advance payment.
Request a free quote