Design guidance for new dwellings at risk of flooding
Reducing flood risk
Our flood risk design guidance is for new dwellings proposed within an area of residual flood risk identified by the Strategic Flood Risk Assessment (SFRA) You can find out more about the SFRA on our SFRA level one, and SFRA level two pages.
It sets out the range of flood resilient/resistant construction/design measures which we expect to be built into any proposals for new residential development in flood risk areas. The aim of these measures is to reduce the risk of flooding to both the property and its future occupants.
Please note, new dwellings in flood risk areas will also need to pass the National Planning Policy Framework Sequential and Exception tests.
The range and type of resiliency measures required depend on the flood depths predicted. They should take into account site specific issues.
Flood depths can be identified using the:
- SFRA
- Tidal Hazard Mapping available from the Environment Agency and
- site specific Flood Risk Assessment (FRA)
If the proposals don’t include sufficient flood mitigation and resiliency measures, as set out below, we’ll refuse the application on flood risk grounds.
Sufficient information needs to be submitted to support the FRA. This should include site plans, elevation drawings and proposed site plans to clearly demonstrate what measures have been included within the design.
Please note, we won’t automatically accept the design if it includes all the appropriate flood resiliency measures. The design must also respect the form and character of the surrounding area. It should respect the amenity of any neighbouring residential properties.
Water depths of up to one metre
Where the FRA shows depths of up to one metre the site specific FRA (in combination with detailed topographical information) must identify the:
- precise flood risk to the site, and
- necessary mitigation measures
The flood mitigation measures should include the following resistance measures:
- finished floor levels to be raised to the predicted flood depth
- dam boards or flood doors
Where internal flooding is unavoidable (and deemed acceptable) the following measures need to be taken:
- resilience measures
- provision of safe refuge above the predicted flood depth
- no ground floor sleeping accommodation
Water depths of over one metre and up to two metres
Where the FRA shows depths of over one metre and up to two metres the site specific FRA (in combination with detailed topographical information) must identify the:
- precise flood risk to the site, and
- necessary mitigation measures
The mitigation measures should include the following resistance measures:
- finished floor levels to be raised to the predicted flood depth
- dam boards or flood doors
Where internal flooding is unavoidable (and deemed acceptable) the following measures need to be taken:
- resilience measures
- provision of safe refuge above the predicted flood depth
- no ground floor sleeping accommodation
OR
- no habitable ground floor accommodation where the above measures can’t be feasibly implemented
Water depths of over two metres
Where the FRA shows depths over two metres:
No ground floor habitable accommodation should be provided. Habitable accommodation includes:
- bedrooms
- sitting rooms
- dining rooms
- kitchens
- any room designed for habitation
Rooms that are not usually used for living in are not considered habitable, such as:
- toilets
- storerooms
- pantries
- garages
This is because flood resistant measures (such as raising finished floor levels and dam boards) wouldn’t be able to stop the ground floor being inundated.
Also, using dam boards to keep a building dry with two or more metres of water around it would probably, due to hydrostatic pressures, lead to its structural failure. So only non-habitable accommodation is allowed on ground floors, allowing water to enter with minimal damage to the property.