How much does a flood risk assessment cost in London?

Do you need one?

Price row: the flood risk assessment is £375, no VAT to add. It is written and ordered on our sister site Fixed Fee Plans, run by the same team.

Start with the flood zone. The GOV.UK guidance says an assessment should be completed for all development, including minor development and changes of use, in Flood Zones 2 or 3, and in Zone 3b, the functional floodplain.

Other triggers apply in Zone 1: a site of 1 hectare or more, a site shown at risk of surface water flooding now or in future, a site in an area with critical drainage problems, and a site that the council’s strategic flood risk assessment shows will be at increased risk.

What “minor” means, and why it keeps the fee modest

A minor extension has its own, lighter route.

The guidance defines a minor extension as a household or non-domestic extension with a floor space of no more than 250 square metres. In Flood Zones 2, 3 and 3b the Environment Agency has standing advice for minor extensions that an applicant follows.

That is why a simple householder assessment can be modest. Ours is £375 for a minor householder project. A new dwelling or a larger scheme is a different, larger job, which we quote after seeing the site.

Can you do it yourself?

The guidance says you will usually need to pay a flood risk specialist, with an exception for a simple, low-risk development, for example a house extension, where you may be able to do it yourself. It adds that if you are not sure, you should contact the Environment Agency for advice.

Our view is simple. If you are in Zone 1 with no surface water risk, you may not need one. If you are in Zone 2 or 3, the cost of an assessment is small next to the risk of the council refusing the application without one.

What goes wrong without one

The guidance is clear that the council may refuse an application if you do not include a required assessment, or if it is not satisfactory. A refusal means a new application and a new council fee, which for one house is £548.

The zone can also change with climate: the guidance lists sites within Flood Zones plus Climate Change among those needing an assessment. We check the current flood map for planning, so the answer is the current one.