Flood zones 1, 2, 3 and 3b explained

What flood zones are for

Flood zones come from the Environment Agency’s Flood Map for Planning. They exist so that councils and developers can steer new buildings away from the land most likely to flood, and so that planning applications are judged consistently. They are a planning tool first. Buyers, owners and insurers use them too, but they were not designed to answer the question “will my house flood?”

The zones in plain terms

According to GOV.UK planning practice guidance on flood risk and coastal change, the zones are defined by the yearly chance of flooding from rivers or the sea:

• Flood Zone 1 is land with less than a 1 in 1,000 chance of river or sea flooding in any year. It is shown as clear on the map, which means Flood Zone 1 is simply everything that is not in zone 2 or 3.
• Flood Zone 2 is land with between a 1 in 1,000 and a 1 in 100 yearly chance of river flooding, or between 1 in 1,000 and 1 in 200 for the sea.
• Flood Zone 3 (also called 3a) is land with a 1 in 100 or greater yearly chance of river flooding, or 1 in 200 or greater for the sea.
• Flood Zone 3b is the functional floodplain: land where water has to flow or be stored in times of flood. Councils identify it in their Strategic Flood Risk Assessment, agreed with the Environment Agency. It normally includes land with a 3.3% (about 1 in 30) or greater yearly chance of flooding where defences work as intended, and land deliberately designed to flood. On the public map, zone 3b is not shown separately from zone 3.

A 1 in 100 chance sounds remote, but it is not a once-a-century event on a timetable. Over a typical 25 year mortgage, a property with a 1% yearly chance has a meaningful chance of seeing at least one such flood. That is why zone 3 matters for lenders and insurers as well as planners.

What the zones leave out

Flood zones are about rivers and the sea only. They say nothing about surface water (heavy rain that cannot drain away), sewers, groundwater or reservoirs. A home can be firmly in zone 1 and still flood.

The zones also take a deliberate view of flood defences. For planning decisions, the guidance says that existing flood risk management infrastructure should initially be ignored, because its long-term funding and maintenance cannot be guaranteed. The practical effect is that a home behind a well maintained embankment can sit in zone 3 while its real, defended risk is much lower. The Environment Agency’s separate Risk of Flooding from Rivers and Sea map does take defences into account. Our page on the different flood maps explains how the two relate.

Finally, the map is a model of the land, not a survey of your garden. Zone edges are drawn on ground heights and river models, and a boundary through a street does not mean the houses on one side are safe and the other side is not.

The sequential test and the exception test

When someone wants to build in a flood zone, councils apply two tests. The sequential test asks whether the development could reasonably go on land with a lower flood risk, and new building should go to zone 1 first, then zone 2, and into zone 3 only if nothing better is available. The exception test applies only for some types of development once the sequential test has been passed. It asks whether the development brings wider benefits to the community that outweigh the flood risk, and whether it will be safe for its lifetime without increasing flood risk elsewhere. Both are decided by the local planning authority, so this is an outline, not a forecast of what your council will do.

When a flood risk assessment is needed

GOV.UK guidance on flood risk assessments for planning applications says an assessment is needed for sites in zone 2 or 3, and for sites in zone 1 that are one hectare or larger. It is also needed for smaller zone 1 sites where the flood map shows surface water risk, or where the council’s own flood risk work shows the risk will rise. Anyone planning an extension or a new building should ask the planning department early, because a missing or weak assessment is a common reason for an application being refused.

Using zones when you buy or insure

If you are buying, treat the zone as a prompt to look further, not as a verdict. Zone 1 does not remove the need to check surface water, and zone 3 does not mean the property floods regularly. Look at the river and sea risk bands, the surface water map, any recorded flood history, and ask your conveyancer for a flood or environmental search. Our guide to buying a house in a flood zone walks through the steps, and the guide to flood insurance covers cover and cost. Insurers use their own risk models, so your zone does not decide your premium on its own.

Check your own postcode

See the flood zone and the risk bands for any English postcode, free of charge.

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