Sequential test or exception test: which one applies

The sequential test and the exception test answer different questions, and the sequential test comes first. Sequential test vs exception test confusion usually shows up the same way: an applicant offers raised finished floor levels as the answer to the sequential test. Design mitigation is irrelevant to the sequential test, which is purely about whether the development could go somewhere at lower flood risk. The exception test is where safety and sustainability benefits are weighed, and only some flood zone and vulnerability combinations reach it at all.

Work out which tests apply before you commission anything. Many sites need the first and never reach the second.

What each test asks

The sequential test asks whether there are reasonably available sites appropriate for the proposed development in areas with a lower probability of flooding. It is a locational test applied to the development, not to the design.

The exception test asks two things about a development that has passed the sequential test but is still proposed in a higher risk location: whether it would provide wider sustainability benefits to the community that outweigh the flood risk, and whether it will be safe for its lifetime without increasing flood risk elsewhere, and where possible will reduce flood risk overall.

The difference in subject matter is the thing to hold on to. One is about where. The other is about whether, given that it has to be here, the development is acceptable and safe. A site-specific Flood Risk Assessment is the evidence for the second limb of the exception test and contributes almost nothing to the sequential test.

The order in which they are applied

Sequential first, always, and the exception test only if it is triggered.

That order has a practical consequence for the evidence programme. There is no point commissioning detailed modelling, finished floor level design and an evacuation plan for a site that cannot pass the sequential test, because the authority will stop at the first hurdle. Equally, a scheme that passes the sequential test and sits in a zone and vulnerability combination where the exception test is not triggered does not need the exception test evidence at all, and offering it invites questions you did not need to answer.

Several categories fall outside the sequential test. Development in Flood Zone 1 with no other source of flood risk, householder development, minor development, and a change of use other than to a caravan, camping or chalet site or a mobile home or park home site are the usual exemptions. Development on a site allocated in an adopted plan is also normally exempt, because the test was applied at plan-making stage, although an authority can still require it where circumstances have changed since adoption.

Do not assume surface water is outside the picture. The sequential approach applies to all sources of flooding, so a site in Flood Zone 1 with a recorded surface water flow path across it can still attract the test.

Sites where the sequential test can be passed

Passing the sequential test is an evidence exercise, and the area of search is the whole argument.

Agree the area of search with the authority before you start. For a market housing scheme the search area is usually the administrative area or a defined part of it. For a scheme meeting a specific local need, a school serving a catchment or an extension to an existing business, a tighter area is defensible, and the justification for narrowing it has to be in the submission rather than assumed.

Then search properly. Use the authority's own housing and employment land availability assessments, the brownfield register, allocations in the adopted and emerging plans, agents' listings and sites with extant permissions. For each candidate site, record whether it is available, whether it is suitable for the development proposed, and whether it is in a lower flood zone, with a dated source for each conclusion.

The three reasons a sequential test usually fails are worth stating plainly. The area of search was drawn too tightly without justification. Sites were dismissed as unsuitable on grounds that reflect the applicant's business model rather than the development type. Or the search was done at a point in time that is now out of date, which matters because availability changes.

When the exception test is triggered at all

Triggering depends on the flood zone and on the flood risk vulnerability classification of the use. Vulnerability runs across essential infrastructure, highly vulnerable, more vulnerable, less vulnerable and water-compatible development.

Residential development is more vulnerable, which is why housing in Flood Zone 3a routinely reaches the exception test and housing in Flood Zone 2 does not. Basement dwellings and caravan sites for permanent occupation sit in the highly vulnerable class, which is why a basement flat in Zone 3a is not an appropriate use however well it is designed.

Check the classification of your actual use rather than assuming. A care home, a hostel and student accommodation are not all in the same class, and the difference changes everything about the application.

The two limbs of the exception test

Both limbs have to be passed, and a failure on either ends the matter.

The first limb is about wider sustainability benefits to the community, and the evidence is a planning argument rather than a technical one. Delivery of housing against a shortfall in land supply, affordable housing, regeneration of a derelict site, a new facility serving a community need and the remediation of contaminated land have all been used. Quantify them, and connect the benefit to the community rather than to the applicant. Verify the current wording of this limb against the Framework in force when you write, because the flood risk policies have been revised more than once.

The second limb is the technical one and the Exception Test submission stands or falls on the flood risk assessment behind it. Expect to show finished floor levels above the modelled design flood level with freeboard, safe access and egress in the design event, climate change allowances applied for the relevant river basin and the lifetime of the development, compensatory storage on a level-for-level basis where development is in the floodplain, no increase in flood risk elsewhere, a flood warning and evacuation plan where dry access cannot be achieved, and an assessment of residual risk including breach and blockage scenarios.

Safe for its lifetime means a stated lifetime. For residential development that is normally taken as 100 years, which drives the climate change allowance used.

Evidence each test needs

Keep the two evidence bases separate in the submission, because a combined document invites the authority to say the sequential test was never properly done.

A Sequential Test submission needs the agreed area of search and its justification, the sources searched with dates, the schedule of sites considered, the reason each was discounted, and a conclusion that no reasonably available site exists at lower risk. Nothing about design belongs in it.

The exception test submission needs the sustainability benefits case with evidence for each benefit, then the flood risk assessment addressing safety. Where the authority or the Environment Agency has model outputs for the watercourse, use them rather than building a new model, and if you do commission modelling, agree the scope first.

Where applicants conflate the two

Four errors account for most refusals and most delays.

1. Offering mitigation as a sequential test answer. Raised floor levels, flood resilient construction and an evacuation plan are second limb exception test matters. They cannot make a site sequentially preferable.
2. Submitting a flood risk assessment and calling it an exception test. The assessment covers the second limb only, and the sustainability benefits limb needs its own section with its own evidence.
3. Applying the exception test when it is not triggered, which wastes fees and signals that the vulnerability classification was not checked.
4. Treating the tests as site-specific when the sequential test is about alternative sites. An applicant who owns one site still has to show no reasonably available alternative exists, and ownership is not a reason to discount other sites.

The same pattern of confused pairs appears elsewhere in the system, as our notes on travel plans and transport statements and on fire statements and fire safety strategies set out.

Browse all 66 report types on PlanScope to see how the flood documents fit together.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.