Permitted Development: Do I need a Flood Risk Assessment?

Permitted development rights (PDRs) are rights to make certain changes to a building without the need to apply for planning permission. Before some PDRs can be used, the developer must first obtain “prior approval” in relation to specified aspects of the development from the Local Planning Authority (LPA).

Do I need a flood risk assessment when applying for prior approval?

If your project falls into one of the classifications below and the building/land is within flood zone 2 or 3 then it is a statutory requirement to submit a site-specific flood risk assessment to your local authority. Other reports may be requested by the local authority such as a contaminated land report and/or mitigation documents, for example a decontamination strategy. If the project is deemed to be in flood zone 1 it is unlikely the proposal would raise any flooding issues unless the area has critical drainage problems or is at risk of surface water or groundwater flooding.

  • Mixed Use – Class M
  • Office to Residential – Class O
  • Storage/Distribution to Residential – Class P
  • Agricultural Buildings to dwellings – Class Q
  • Agricultural Buildings to Commercial – Class R
  • Agricultural Buildings to schools or nurseries – Class S
  • Land/buildings to schools and nurseries – class T

Planning Policy Guidance (PPG) also states that to assist LPAs on whether prior approval is required in an area at risk of flooding, the applicant should provide:

“an assessment of flood risk. This should demonstrate how the flood risks to the development will be managed so that it remains safe through its lifetime.”

What type of changes do not require a flood risk assessment?

For the following classifications there is no mandatory requirement to get a flood risk assessment:

  • Enlargement, improvement or alteration– Class A
  • Additions to the roof– Class B
  • Other alterations to the roof– Class C
  • Porches– Class D
  • Outbuildings – Class E

However, as part of obtaining the Lawful Certificate of Development, the LPA may want to check that the alterations, particularly to the footprint of the house, do not increase the chance of flooding neighbouring properties through the use of permeable building materials.

Do I need planning permission to upgrade my driveway?

You will not need planning permission if a new or replacement driveway of any size uses permeable (or porous) surfacing which allows water to drain through, such as gravel, permeable concrete block paving or porous asphalt, or if the rainwater is directed to a lawn or border to drain naturally.

If the surface to be covered is more than five square metres, planning permission will be needed for laying traditional, impermeable driveways that do not provide for the water to run to a permeable area. In order to prevent flood risk to neighbouring third parties a sustainable drainage report may be required

Note this only applies to houses and not flats, maisonettes or converted houses created through permitted development rights.

The permitted development rights only apply to front gardens and you may require planning permission for fences, walls, gates or a dropped kerb.permitted development flood

What should I do if the permitted development falls into a flood risk area?

Where the proposed permitted development is in a qualifying flood risk situation, you will need to provide a plan showing the finished floor levels and the estimated flood levels.

Government standing advice states that floor levels should be either no lower than existing floor levels or 300mm above the estimated flood level.

If they are not, you may also need to consider extra flood resistance and resilience measures. These need to follow the guidance on improving the flood performance of new buildings.

Your plans need to show how you’re going to ensure the development is not flooded by surface water. An example of this could be to divert surface water away from the property or by using flood barriers.

If your minor extension is in an area with increased flood risk as a result of multiple minor extensions in the area, you will need to include an assessment of the off-site flood risk. Your LPA will advise if this applies to your development.

Can permitted development be refused?

In some circumstances, LPAs can suspend permitted development rights in their area, under Article 4 of the 2015 Order. The Secretary of State must be notified, and has wide powers to modify or cancel most article 4 directions.

When considering the potential impacts of permitted development on local flood risk, an LPA “may consider” making an article 4 direction to “protect local amenity or the well-being of an area.”

Get a Clearer Picture

GeoSmart understands how river, surface and groundwater flooding can affect property and development sites.  Our expert flood risk consultants will advise on flood zones and constraints, as well as potential vulnerabilities that could impact on your client’s permitted development project.

For more information about our desktop flood risk assessments and contaminated land risk assessments call us on 01743 298 100 or email