The sequential test section inside a Flood Risk Assessment

The sequential test section of a Flood Risk Assessment answers one question: are there reasonably available sites at lower flood risk that could accommodate this development. It is not a description of the site's flood risk, and it is not the exception test. Written well it runs to three or four pages, carries an area of search that the officer can defend, and ends in a conclusion the officer can lift into the report almost unchanged.

Written badly, it asserts that no alternative sites exist and offers nothing to support the assertion. That is the version that produces a holding objection and three months of correspondence.

Who applies the test, and what that means for your drafting

The sequential test is applied by the local planning authority, not by the applicant. The applicant provides the evidence, the authority reaches the conclusion, and the decision notice records it.

That division changes how the section should read. You are not arguing a case so much as assembling a defensible evidence base and setting out the reasoning an officer would follow. Write it in terms the officer can adopt: state the search parameters, show the method, list what was found, and explain the outcome against the policy test rather than against the merits of your client's scheme.

Where the authority has its own published methodology for sequential test evidence, follow it exactly, including any pro forma. Officers reading a familiar format find what they need quickly.

Defining the area of search and justifying it

The area of search is the point on which most sequential tests turn, and it is the one that repays careful drafting.

The default is the administrative area of the local planning authority. Departing from that default needs a reason rooted in the development itself rather than in the applicant's preferences. Reasons that carry weight include a functional requirement to be in a particular place, a defined catchment for a facility such as a school or health centre, an operational link to an existing business, or a development plan allocation that sets the geography.

Reasons that do not carry weight include land ownership, the applicant's business area, the cost of alternative land, and a search area drawn to exclude the sites that would otherwise be found.

Set the parameters out explicitly at the start of the section: geographical area and the justification for it, the date of the search, the site size range considered, the development type the alternatives must be able to accommodate, and any functional requirement that constrains the answer. A search for a 40 unit residential scheme should not be filtering out sites capable of 30 units unless you say why.

Identifying reasonably available sites

Reasonably available means available now or in a reasonable time, not theoretically developable. The usual sources are the authority's strategic housing and employment land availability assessments, the adopted local plan allocations, the brownfield land register, the authority's list of sites with extant permission, and commercial agents' listings at a stated date.

Record the search as a table. For each site identified, give the reference, the size, the flood zone, whether it is available and when, and the reason it is or is not a reasonable alternative. A site discounted because it is already under construction is a legitimate exclusion. A site discounted because someone else owns it is not.

Two practices strengthen the section. State a cut-off date and stick to it, so the search can be repeated and checked. And include the sites you discounted rather than only the ones that survived, because a table that lists nothing but rejections looks like a search designed backwards.

The full report structure around this section sits in the Flood Risk Assessment, and where the test is being carried out as a standalone exercise it forms the Sequential Test (Flood Risk) document in its own right.

Comparing sites on flood zone and vulnerability

The comparison is between flood risk at the alternative sites and flood risk at the application site, using the flood zones from the Flood Map for Planning together with the authority's strategic flood risk assessment, which usually distinguishes Zone 3a from the functional floodplain at 3b.

Vulnerability classification matters as much as the zone. The planning practice guidance on flood risk and coastal change sets out the vulnerability categories and the combinations of zone and vulnerability that are acceptable, those that require the exception test, and those that should not be permitted. A more vulnerable use in Zone 3a is in a different position from a less vulnerable use on the same land.

Two refinements are worth including where they apply. Other sources of flooding, including surface water, groundwater, sewers and reservoirs, form part of the picture, so a comparison based on fluvial zones alone can be incomplete. And climate change allowances shift the picture over the lifetime of the development, so a site that compares well today may not compare well over a 100 year residential lifetime.

The sequential approach within a single site

Where the site itself contains areas of different risk, the sequential approach applies inside the red line. The drafting should show it, not merely claim it.

That means putting the more vulnerable uses in the lowest risk part of the site, keeping the functional floodplain free of built development, locating vehicular access and emergency egress through lower risk land, and setting finished floor levels above the modelled level plus freeboard. Where the layout has been changed to achieve this, say so and show the earlier option. An officer who can see the design responded to flood risk reads the whole report differently.

Where the test is not required

The test does not apply to every application, and time is wasted on sections that were never needed.

Confirm the position in the current planning practice guidance rather than from an earlier report, because the scope of the test has been adjusted more than once.

Writing the conclusion so an officer can adopt it

The conclusion is four sentences, not four paragraphs. State the area of search and its justification. State what was searched and on what date. State the finding: whether reasonably available sites at lower risk capable of accommodating the development were identified. And state the consequence, which is either that the test is passed or that the exception test is engaged and is addressed in the following section.

Avoid two habits. Do not conclude that the site "is considered acceptable in flood risk terms", because that conclusion belongs to the authority and not to you. And do not fold the exception test into the same paragraph, because the two tests ask different questions and merging them invites a consultee to say neither has been done properly. The Exception Test (Flood Risk) belongs in its own section with its own evidence.

One honest caveat. A well-evidenced sequential test can still fail, because the answer depends on what is out there rather than on how well you write. Running the search at feasibility stage, before the land is committed, is the only real protection.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and verify the current flood risk guidance and the applicable NPPF edition at the time of writing.

PlanScope can draft the sequential test structure and the site comparison table from your search inputs. Enter your postcode to see which reports your site needs. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.