Flood risk sequential and exception tests

Sequential and exception tests are tools advised by the National Planning Policy Framework to help local authorities ensure sites with the lowest risk of flooding are being developed.

If work is required in a flood zone, the exception test will need to assert why the development needs to make use of that particular site, and ensure its future safety. 

Sequential test

As noted in section 14, paragraph 158 of the National Planning Policy Framework: 

The aim of the sequential test is to steer new development to areas with the lowest risk of flooding. Development should not be allocated or permitted if there are reasonably available sites appropriate for the proposed development in areas with a lower risk of flooding. The strategic flood risk assessment will provide the basis for applying this test. The sequential approach should be used in areas known to be at risk now or in the future from any form of flooding.

If your development is in Flood Zones 2 and 3, you will need to gather evidence to allow us to consider whether a sequential test is satisfied. The evidence needs to show that there are no other suitable sites with a lower flood risk.


The report needs to include the following: 

  • Location and background of the site and reason for the test
  • Site analysis
  • Local policy review
  • Criteria used in site assessment
  • Sequential test - this can include a review of the local authority plans in relation to the site and comparisons to other sites

Exception test

Some development types are not allowed in a flood zone unless there are exceptional circumstances. We consider these using the exception test, which is only used when the sequential test is passed. For more information section 14 of the National Planning Policy Framework. 

An exception test is required for developments in the below classes:

  • highly vulnerable (in flood zone 2)
  • essential infrastructure (in flood zone 3a and 3b)
  • more vulnerable (in flood zone 3a)


To pass the exception test you must:

  • show the development gives wider sustainability benefits to the community that outweigh a flood risk
  • show the development will be safe for its lifetime considering the vulnerability of users and reducing flood risk on the development without increasing flood risk elsewhere.

When sequential and exception tests are not required

Flood risk sequential and exception tests are not required for the following:

  • minor non-residential extensions (industrial/commercial/leisure etc) with a footprint less than 250sqm
  • development that does not increase the size of buildings
  • householder development (sheds, garages, games rooms etc.) within the curtilage of the existing dwelling in addition to physical extensions to the existing dwelling itself. This definition excludes any proposed development that would create a separate dwelling within the curtilage of the existing dwelling, such as a subdivision of houses into flats
  • changes of use except for change to a caravan, camping or chalet site, or to a mobile home or park home site.

We have prepared detailed advice about how both the Sequential Test and the Exception Test will be considered in relation to flood risk issues in North Somerset. The advice is based upon national policy and guidance, the council’s adopted planning policies, and detailed discussions with the Environment Agency.