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The Sequential Test for new housing development - Christchurch

The National Planning Policy Framework (NPPF) requires local planning authorities to follow a risk-based approach in their consideration of applications for new development. The first stage of this approach is the Sequential Test which aims to steer new development to areas with the lowest probability of flooding. Only when there are no reasonably available alternative sites within zone 1 (low probability) can development within zone 2 (medium probability) or zone 3 (high probability) be considered.

To support the Sequential Test, Christchurch Borough Council has produced a Strategic Flood Risk Assessment that together with current day flood risk, shows Flood Zones one, two and three in the years 2093 and 2113. This has been done to ensure development is safe for its full design life; 60 years in the case of commercial developments and 100 years for housing.

This page explains the process of conducting the Sequential Test for housing required by the National Planning Policy Framework, and supported by the National Planning Practice Guidance.  Advice for commercial developments can be found on the sequential test for commercial development in Christchurch page.

Reasonably available alternative sites

Prior to consideration of any development within a flood zone in Christchurch, a Sequential Test must be conducted to demonstrate that no reasonably available alternative sites exist within flood zone one which could be developed instead. Christchurch has a joint housing target with East Dorset and the Christchurch Strategic Housing Land Availability Assessment (SHLAA)  together with the East Dorset SHLAA identify potential sites for new housing across the plan area and estimates how many new dwellings could be accommodated on each, called the net potential. Sites within the first five year supply of housing sites identified by the SHLAAs must be considered suitable, available and achievable, and therefore developable.

Applicants proposing new housing within Flood Zones two or three will need to demonstrate that none of the sites identified in the schedule set out in the Christchurch and East Dorset Five Year Housing Land Supply document are reasonably available alternatives at lower risk of flooding.

Our advice, with support of the Environment Agency, is that reasonably available alternative sites include not only sites of a similar size and dwelling capacity to the one being tested, but also smaller sites which could cumulatively provide the same number of dwellings. For a development of 12 houses for example, the Sequential Test should consider that the same number of houses could be accommodated on two sites of six dwellings each, or three sites of four dwellings each, or indeed any other combination of smaller sites.

Intensification of residential development on a site in Flood Zone two or three will not pass the Sequential Test. For example, the demolition of one house and replacement with two dwellings will fail the test.

It is highly unlikely therefore that residential development proposed in Flood Zone two or three, where it results in a net increase in dwellings, will pass the Sequential Test. Applicants are advised to speak with planning officers prior to submitting any application for development affected by flood risk.

Which Flood Zones to use?

Following the update of the Christchurch Strategic Flood Risk Assessment (SFRA) in 2017, as a consequence of the greater understanding and enhanced data it provides, agreement has been reached with the Environment Agency on a modified approach to the 'sequential test' in respect of planning applications for windfall sites.

Examples of the approach are set out in a Practice Note. In general terms, the Council now consider that current flood zones set out in Christchurch's SFRA Level 1 study are the starting point for the preparation of evidence used to perform the Sequential test.

However, developers must submit via a detailed Flood Risk Assessment evidence to fully address the relevant climate change forecast flood levels (tidal, fluvial, surface water, sewer) identified in the Christchurch Level 2 SFRA study, and show that the proposed development will be safe throughout its lifetime and will not adversely affect others. 

Evidence to be provided by applicants

The Planning Practice Guidanceplaces the onus on developers to provide the local planning authority with evidence to inform the Sequential Test. Applicants will need to provide the following with all applications for residential development affected by flood risk:

  • Comprehensive site Flood Risk Assessment
  • Evidence that all reasonably available alternative sites have been assessed and discounted (referring to the list of sites within the Christchurch and East Dorset Five Year Housing Land Supply document identified by the current Strategic Housing Land Availability Assessments for Christchurch and East Dorset)
  • Evidence explaining the geographical extent of the area used to identify reasonably available alternative sites - this will invariably be the whole plan area of Christchurch and East Dorset
  • The vulnerability classification of all uses within the development

Environment Agency Standing Advice

Planning applicants and their agents should refer to the Environment Agency Flood Risk Standing Advice for England for guidance on what to do when submitting a planning application.

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