Bath and North East Somerset › Guides › Flood zones 1, 2 and 3

Flood zone 1, 2 and 3 explained

Flood zones show the chance of flooding from rivers and the sea for an area of land: zone 1 is low, zone 2 medium, zone 3 high. They do not cover surface water or groundwater flooding.

What the zones mean

The zones are defined by the yearly chance of flooding from rivers or the sea, ignoring flood defences.

• Zone 1 (low probability): less than a 1 in 1,000 chance each year.
• Zone 2 (medium probability): between 1 in 1,000 and 1 in 100 each year for river flooding, or between 1 in 1,000 and 1 in 200 for the sea.
• Zone 3a (high probability): 1 in 100 or more each year for river flooding, or 1 in 200 or more for the sea.
• Zone 3b (functional floodplain): land where water has to flow or be stored in times of flood.

Zones 2 and 3 do not take account of flood defences or the possible effects of climate change.

What flood zones do not cover

Flood zones map rivers and the sea only. Flood risk also includes rain running off the ground surface (surface water), rising groundwater, overwhelmed sewers and drains, reservoirs, canals and lakes. A home in zone 1 can still flood from these sources.

The Environment Agency publishes separate long-term flood risk information, including surface water, on GOV.UK.

What it means if you own or are buying

• Planning: a flood risk assessment is needed for all development in zones 2 or 3, including minor development and changes of use. In zone 1 one is needed for sites of 1 hectare or more, or where the flood map for planning shows a surface water risk.
• Extensions: for a household extension of no more than 250 square metres, the applicant can follow the Environment Agency's advice for minor extensions instead of a full assessment.
• Insurance and mortgages: flood zones are a planning tool. Insurers and lenders use their own data, so a zone does not tell you what cover will cost or whether a lender will lend. Ask your insurer, lender or conveyancer. (Our note: we have not found an official statement of how they use the zones.)

How we show it

The mapped data is the Environment Agency's Flood Map for Planning, for zones 2 and 3 only; any area we do not map as 2 or 3 is shown as zone 1.

Common questions

What is flood zone 3?

Land with a 1 in 100 or greater yearly chance of river flooding, or 1 in 200 or greater for the sea, ignoring flood defences. Zone 3b, the functional floodplain, is land where water has to flow or be stored in times of flood.

Does flood zone 1 mean a home cannot flood?

No. Zone 1 means less than a 1 in 1,000 yearly chance of river or sea flooding. Surface water, groundwater, sewer and reservoir flooding are not covered by the zones.

Do I need a flood risk assessment to extend my house?

In zones 2 and 3 a flood risk assessment is needed for all development, but for a household extension of up to 250 square metres you can follow the Environment Agency's advice for minor extensions. Ask your council.

Official sources

• Planning practice guidance: Flood risk and coastal change (GOV.UK) (accessed 2 October 2026)
• National Planning Policy Framework, Annex F: Managing flood risk and coastal change (GOV.UK) (accessed 2 October 2026)
• Flood risk assessments: applying for planning permission (GOV.UK) (accessed 2 October 2026)
• Check your long term flood risk (GOV.UK) (accessed 2 October 2026)

General information, not legal, planning or surveying advice. Check with the council and a qualified professional before relying on it. Other guides: Listed building grades (I, II*, II), Conservation areas, Article 4 directions, Tree preservation orders, Agricultural land grades.