Guide
The flood risk sequential test: when you need it and what it costs
Updated
The sequential test steers development to the areas with the lowest flood risk by comparing your site with other available sites. The council may refuse planning permission if a lower risk site is reasonably available.
When it is needed
The Environment Agency's standing advice says a sequential test is required for major and non-major development where any building, access and escape route, land-raising or other vulnerable element will be in Flood Zone 2 or 3, in Flood Zone 3b, in 'Flood Zones plus climate change', or in Flood Zone 1 with a surface water or future risk (gov.uk, flood risk standing advice).
Who is exempt
- Householder development such as residential extensions, conservatories or loft conversions.
- Small non-domestic extensions with a footprint of less than 250 square metres.
- A change of use, except to a caravan, camping or chalet site, or a mobile or park home site.
- A site solely at risk from surface water, where a site-specific flood risk assessment shows it will be safe throughout its lifetime without increasing flood risk elsewhere.
- A site allocated in the development plan through the sequential test, used for its allocated use, with no significant change in the known flood risk.
How it is applied
The standing advice says to speak to the council early to agree the area of search. The council considers whether the test is passed against the land availability information it holds, and you should add any other reasonably available sites it has not identified, including sites on the open market.
Then the exception test
If the sequential test is passed, the exception test may also be needed: for 'highly vulnerable' development in Flood Zone 2, 'more vulnerable' development in Flood Zone 3a, and 'essential infrastructure' in Flood Zone 3a or 3b. Both elements must be satisfied before the council can permit the development.
What it costs
One firm read on 27 October 2026 prints a fixed price for the work: Flood Risk Environmental publishes a sequential and exception test from £395. The others quote it with the flood risk assessment.