"Can I build in a flood zone?" has a precise answer in national policy — it depends on which zone and what you want to build. The NPPF sorts every land use into a flood risk vulnerability class, and a compatibility matrix says whether that use is appropriate in your zone, needs the Exception Test, or should not be permitted at all. This checker does the lookup for you, straight from your postcode.
Flood vulnerability checker
The checker needs JavaScript enabled. The rules it applies are in the PPG flood risk guidance and NPPF Annex 3.
The compatibility matrix behind the tool
| Vulnerability class | Zone 1 | Zone 2 | Zone 3a | Zone 3b |
|---|---|---|---|---|
| Essential infrastructure | Appropriate | Appropriate | Exception Test | Exception Test |
| Water-compatible | Appropriate | Appropriate | Appropriate | Appropriate |
| Highly vulnerable | Appropriate | Exception Test | Not permitted | Not permitted |
| More vulnerable | Appropriate | Appropriate | Exception Test | Not permitted |
| Less vulnerable | Appropriate | Appropriate | Appropriate | Not permitted |
"Appropriate" never means automatic — in Zones 2 and 3 the Sequential Test still applies (the council must be satisfied no reasonably available site at lower risk exists), and a site-specific FRA is still required.
Which class is my development?
- Highly vulnerable — basement dwellings; caravans and park homes for permanent residential use.
- More vulnerable — houses and flats, hotels, care homes, hospitals, pubs and nightclubs.
- Less vulnerable — shops, restaurants and cafés, offices, general industry, storage, agriculture.
- Water-compatible — flood control infrastructure, marinas and boatyards, outdoor sport and amenity space.
- Essential infrastructure — essential transport and utility infrastructure that has to be there.
Sequential Test vs Exception Test — the difference
The Sequential Test asks "could this development go somewhere at lower flood risk?" and applies to most development in Zones 2 and 3. The Exception Test is the higher bar for the riskier combinations in the matrix: you must show wider sustainability benefits that outweigh the risk, and that the development will be safe for its lifetime without increasing risk elsewhere — evidenced through your FRA.
Honest limits
The postcode lookup uses the Environment Agency's Flood Zone 2/3 dataset, which does not separate Zone 3a from 3b — the functional floodplain is defined in your council's Strategic Flood Risk Assessment, so if your site is near a watercourse, check the SFRA and use the tool's manual zone option. Zone 1 results still carry FRA triggers (sites over 1 hectare, surface water, within 20 m of a main river) — see our flood zone checker guide and the 2026 flood statistics for the wider picture.
How Fortress Associates can help
If your combination points to an FRA — and in Zones 2 and 3 it always does — our automated flood risk assessment service produces one in minutes, free, with sequential and exception test support, SuDS strategy to CIRIA C753 and live Environment Agency data, following the EA's March 2025 template. See all services or talk to us about a tricky site.
Sources & further reading
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