Sequential and exception tests: what each one must prove
Two separate documents answering two separate questions. Here is how to define the search area, evidence reasonably available sites, and address both limbs of the exception test.
The sequential test and the exception test for flood risk answer different questions, and validation lists treat them as separate documents because they are. The sequential test asks whether the development could reasonably go somewhere at lower risk. The exception test asks whether, given that it cannot, this particular scheme is justified and safe. Fail the first and the second never gets read.
Applicants merge them into one section of the flood risk assessment and then wonder why the case officer asks for a sequential test.
Why validation lists ask for two documents
A flood risk assessment describes the site: the sources of flooding, the modelled levels, the climate change allowances, the finished floor levels, the residual risk. It is a technical document about one piece of land.
The sequential test is not about the site at all. It is about every other site in the search area that the applicant could have used instead, which is a planning and land availability exercise rather than a hydraulic one. Producing it as a chapter inside the flood risk assessment tends to squeeze it into three paragraphs, when what the council needs is a table of sites with reasons for discounting each one.
The exception test is a policy judgement drawing on both, plus the wider planning merits. Keeping the three apart makes each easier to write and much easier for an officer to reference in the report.
Defining the search area and reasonably available sites
The search area is set by the local planning authority, and you should ask before you start. For a single dwelling it might be a parish or a settlement boundary. For a housing scheme it is normally the whole administrative area, and for a use serving a wider catchment it can be broader still.
Reasonably available sites are those in a suitable location for the type of development proposed, with a reasonable prospect of being available and developable within a reasonable period. Three parts of that wording carry weight. Suitable location means the site could accommodate this development, not any development. Available means there is evidence it could be acquired, so an allocated site with a live consent for something else is arguably not available. And a reasonable period is judged against the delivery timescale of the scheme, not an open-ended horizon.
What the test does not allow is a search restricted to land the applicant already owns. That is the single most common reason a sequential test is rejected.
Evidence that satisfies an officer
Build the sequential test as a table and a method statement, in this order:
- State the search area and who agreed it.
- State the sources searched: the council's strategic housing land availability assessment, brownfield register, site allocations in the adopted plan, the Environment Agency flood map for planning, and commercial property listings where the use is commercial.
- State the date of the search, because a test run two years earlier is out of date.
- List every site identified, with its area, flood zone, current allocation and current status.
- Give a reason for discounting each one, tied to the criteria of suitability, availability and developability.
- Conclude on whether any reasonably available site exists at lower risk.
Reasons have to be evidenced rather than asserted. "Not available" needs a source, whether that is an agent's confirmation, a planning permission for another use, or the council's own monitoring. "Too small" needs the required site area stated. Officers read this section looking for whether you excluded sites because they fail the criteria or because you preferred yours.
Where no reasonably available sites at lower risk exist, say so plainly and move on. A sequential test document that reaches a clear conclusion in four pages beats one that hedges over twenty.
The two limbs of the exception test
The exception test applies where the flood risk vulnerability of the development and the zone it sits in require it, most commonly more vulnerable development such as housing in Flood Zone 3a, or highly vulnerable development in Flood Zone 2. Both limbs must be passed.
The first limb asks whether the development would provide wider sustainability benefits to the community that outweigh the flood risk. This is where affordable housing delivery, the reuse of previously developed land, regeneration of a derelict site, employment, or the release of a constrained site for a community use all get argued. It is a planning case, not a technical one, and it belongs in the planning statement as much as in the flood documents.
The second limb asks whether the development will be safe for its lifetime, taking climate change into account, without increasing flood risk elsewhere and, where possible, reducing flood risk overall. This is the technical limb: finished floor levels, safe access and egress, compensatory storage, flood resilient construction, warning and evacuation arrangements.
Check the current wording of both limbs against the published framework before drafting, because the phrasing has been revised across successive editions and the emphasis on climate change has strengthened. The exception test document should address each limb under its own heading, with the evidence for each stated separately.
Illustrative example: an infill plot in Flood Zone 3a
Take a windfall plot of 0.05 hectares in a village, between two existing houses, wholly within Flood Zone 3a. The proposal is one dwelling. This example is illustrative.
Residential development is more vulnerable, and more vulnerable development in Flood Zone 3a requires the exception test. A single dwelling is not minor development for these purposes, so the sequential test is required too.
The sequential test looks at the parish, or whatever area the council specifies. If the village has three undeveloped plots in Flood Zone 1 with planning permission lapsed or with owners willing to sell, the test fails, and the application will be refused however good the flood risk assessment is. If the village is entirely within Flood Zones 2 and 3 apart from land in a National Landscape with no prospect of release, that is a defensible conclusion, evidenced against the council's own site assessments.
The exception test then has to show a community benefit beyond one more house, which is hard for a single open-market dwelling and easier where the plot delivers something the parish has identified as a need. On the safety limb the scheme would need finished floor levels set above the modelled design flood level plus the appropriate climate change allowance, with freeboard agreed with the lead local flood authority, safe pedestrian access to land above that level, and a warning and evacuation plan.
The sequential approach within the site layout
Separate from the sequential test between sites, national guidance expects a sequential approach within a site. It is easy to do and it is often ignored.
Put the least vulnerable elements in the highest risk part of the site. Parking, landscaping, open space, garaging and access roads can tolerate occasional inundation. Sleeping accommodation cannot. On a sloping site with a flood corridor along one edge, the layout should push the dwellings uphill and use the corridor for green infrastructure, even if that means a less efficient plot layout.
Level-for-level compensatory storage may be needed where any part of the development occupies floodplain, and it has to be provided on land at the same levels and hydraulically connected, which is a constraint that shapes the layout rather than a detail to resolve later.
When the tests are not required
Neither test applies to everything. The sequential test is not required for householder extensions, for minor development, for most changes of use, or for development on sites already allocated through a sequential test at plan-making stage.
Minor development in flood risk terms means non-residential extensions with a footprint below 250 m2, alterations that do not increase the size of the building, and householder development such as extensions and conservatories. Changes of use are generally exempt, with the notable exception of a change to a caravan, camping or chalet site, which is treated as sensitive because of the vulnerability of the occupants.
The exception test is required only where the vulnerability and zone combination calls for it. Check the vulnerability classification and the zone table in the guidance rather than assuming, because misclassifying the development is a faster route to refusal than any technical error.
This is general guidance, not legal advice. Flood zone boundaries, climate change allowances and the guidance itself are revised, so check the current published position with your local planning authority, the lead local flood authority or a qualified professional before relying on it.
Browse the 66 PlanScope report types to see how the flood documents fit together in an application pack. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What is the difference between the sequential test and the exception test?
The sequential test asks whether the development could reasonably be located on a site at lower flood risk, which is a land availability exercise across a defined search area. The exception test asks whether a development that cannot go elsewhere is justified by wider sustainability benefits and will be safe for its lifetime. The sequential test comes first.
How is the search area for a sequential test decided?
By the local planning authority, so ask before starting. For a single dwelling it may be a parish or settlement boundary, for a housing scheme it is usually the whole administrative area, and for a use serving a wider catchment it can be broader. A search limited to land the applicant already owns will be rejected.
What makes a site reasonably available?
It must be in a suitable location for the type of development proposed, with a reasonable prospect of being available and developable within a reasonable period. Each limb needs evidence. Discounting a site as unavailable requires a source, such as an agent's confirmation, an extant permission for another use, or the council's own monitoring data.
When is the exception test required?
Where the combination of flood zone and flood risk vulnerability calls for it, most commonly more vulnerable development such as housing in Flood Zone 3a, and highly vulnerable development in Flood Zone 2. Both limbs have to be passed: wider sustainability benefits that outweigh the flood risk, and safety for the lifetime of the development.
Do householder extensions need a sequential test?
No. The sequential test is not required for householder development such as extensions and conservatories, for minor non-residential extensions with a footprint below 250 m2, for alterations that do not increase building size, for most changes of use, or for sites already allocated through a sequential test at plan-making stage.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.