Flood Zone 3 is the Environment Agency's high-probability flood zone. Here is what it means for planning, buying and insurance. Paste an address or postcode below to check its zone, or a whole list.
Quick answer
Flood Zone 3 is land in England with a high probability of flooding: a 1% (1 in 100) or greater chance each year from rivers, or 0.5% (1 in 200) or greater from the sea, ignoring flood defences. Any planning application there needs a site-specific flood risk assessment. Councils divide it into Flood Zone 3a (high probability) and Flood Zone 3b (the functional floodplain, where water has to flow or be stored in a flood), where almost no new development is allowed.
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UK addresses with a postcode, or postcodes on their own. Only the address is used for the check.
The Environment Agency maps Flood Zone 3 as one zone. Each council's strategic flood risk assessment marks the functional floodplain, Flood Zone 3b, inside it: land where water has to flow or be stored in times of flood. The rest is Flood Zone 3a. This checker shows Flood Zone 3; the council's strategic flood risk assessment shows whether a site is 3b.
Planning practice guidance sorts uses by flood vulnerability. In Flood Zone 3a, less vulnerable uses (shops, offices, industry) and water-compatible uses are appropriate; homes and other more vulnerable uses, and essential infrastructure, need the exception test; highly vulnerable uses (basement dwellings, permanent caravans, police and fire stations needed in a flood) shouldn't be permitted. In Flood Zone 3b only water-compatible development, and essential infrastructure that passes the exception test, is allowed. The sequential test comes first: is there a reasonably available site at lower risk?
Homes in Flood Zone 3 are bought, mortgaged and insured every day, but lenders and insurers will ask about flood risk and premiums can be higher. Flood Re, the scheme run by the government and insurers, helps keep home insurance affordable for homes built before 2009. The zone describes the land, not the house: a building with raised floors, or behind good defences, may be at much lower actual risk.
A guide and a screening check, not a flood risk assessment. For a planning application, get the official flood map for planning report for the site from GOV.UK.
What does Flood Zone 3 mean?
Land with a high probability of flooding: a 1% or greater annual chance from rivers, or 0.5% or greater from the sea, ignoring flood defences.
What is the difference between Flood Zone 3a and 3b?
3b is the functional floodplain, where water has to flow or be stored in a flood, marked by the council's strategic flood risk assessment. 3a is the rest of Flood Zone 3. Almost no new development is allowed in 3b.
Can you build a house in Flood Zone 3?
In Flood Zone 3a, only if it passes the sequential test and the exception test, with a flood risk assessment showing it will be safe for its lifetime. In Flood Zone 3b, no.
Do I need a flood risk assessment in Flood Zone 3?
Yes, for any development, including extensions and changes of use.
Can I get a mortgage in Flood Zone 3?
Usually, yes, if the property can be insured. Flood Re helps keep home insurance affordable for most homes built before 2009.
How do I check if an address is in Flood Zone 3?
Enter it in the checker above. It looks the address up in the Environment Agency's Flood Zones (July 2026 release).