Flood Risk Assessment

A flood risk assessment (FRA) is the site-specific report a local planning authority needs before it can grant permission where flooding is a factor. Unda prepares these assessments across England and Wales, built to the National Planning Policy Framework that came into force on 17 August 2026, so planning officers and the Environment Agency get the evidence a decision actually rests on. We are a CIWEM Business Partner, our reports are signed off by chartered flood risk consultants, and we are rated 5.0 on Google.

Most people arrive here having been told they need an FRA and wanting two things: to know what that means for their scheme, and to get it done without holding up the application. This page explains what an assessment covers, when one is required, how the August 2026 policy changes affect you, and how to get a quote the same working day.

A flood risk flag on your site does not mean the application will be refused. It means the risk has to be understood and managed with evidence, which is exactly what a good assessment does.

What is a flood risk assessment?

A flood risk assessment is a technical report that establishes how flooding could affect a development, and how the layout and design keep people and property safe for the lifetime of the scheme without pushing risk onto neighbours. It looks at every source that applies to the site, from rivers and the sea to surface water, groundwater and drainage, and sets the findings against national planning policy so the case officer can determine the application.

An FRA for planning is a different document from a homebuyer’s flood risk survey for a property purchase and from a lender’s insurance report. If you are not certain which one you need, our flood risk consultants will point you to the right report before you commit to anything. The technical terms used throughout an assessment, from functional floodplain to attenuation, are set out in plain language in our flood risk and drainage glossary.

Flood risk is not a niche concern. The Environment Agency’s latest national assessment, NaFRA2, puts around 6.3 million properties in England at risk from rivers and the sea and around 4.6 million at risk from surface water, with the two overlapping. That is the backdrop against which local authorities now ask for site-specific evidence, and why the way flood risk is mapped and managed matters to almost every planning application near water.

When is a flood risk assessment required?

The short answer is that you need one whenever your site carries a real prospect of flooding, or your development could make flooding worse somewhere else. In practice that covers a wider set of sites than many applicants expect, and the August 2026 policy changes widened it further.

• Sites in Flood Zone 2 or 3. Any development in the medium or high river and sea flood zones needs a site-specific assessment, whatever its size.
• Larger sites in Flood Zone 1. Development of a hectare or more in the lowest-risk zone still needs an FRA, because scale changes runoff and drainage.
• Any site the maps flag for other sources. Under the new Framework, an assessment is now required wherever the Flood Map for Planning or the local strategic flood risk assessment shows land at risk from any source, now or in the future. The old qualifier that this only applied when the use became more vulnerable has been removed, so surface water risk alone can now trigger the requirement in Flood Zone 1.
• Changes of use and vulnerable uses. Turning a building into housing, a care home or other more vulnerable use in a risk area will need an assessment, and the vulnerability classification decides what is acceptable where.
• Where a consultee asks for one. The Environment Agency, a lead local flood authority or the case officer can request an assessment on any site they consider at risk.

Because the updated Flood Map for Planning now shows surface water climate change extents, land that read as clear a year ago can now sit inside a mapped risk area. If you are unsure whether your site is caught, our free flood risk map postcode checker is a sensible first look, and you can see current conditions on the live river levels map.

Which type of flood risk assessment do you need?

Flood risk assessment is a broad label, and the right report depends on why you have been asked for one. Use this to find your route, or tell us the situation and we will confirm it.

• Planning application flagged for flood risk. You need a flood risk assessment for planning, the core report a local authority requires to determine a scheme.
• Told to prove your site is sequentially preferable. That is a sequential and exception test report, often needed alongside the FRA in Flood Zone 2 or 3.
• Site in Wales. Wales works to TAN15 and needs a flood consequence assessment rather than an FRA.
• Buying or selling a home. A flood risk survey for a property purchase answers a buyer’s questions; it is not a planning document.
• Mortgage or insurance query. A flood risk assessment for insurance speaks to lenders and underwriters.
• Chasing a BREEAM credit. A BREEAM flood risk assessment meets the Pol 03 requirements.
• Groundwater is the concern. A groundwater flood risk assessment deals with high water tables and cellars.
• Complex hydraulics or a disputed flood level. That calls for detailed flood modelling to establish defensible levels.

If none of these quite fits, contact us with a description of the site and the planning position, and we will tell you which report the authority will accept.

What the August 2026 NPPF means for your flood risk assessment

The National Planning Policy Framework is the policy your case officer applies, and a new version replaced the December 2024 Framework on 17 August 2026. Flood risk now sits in a dedicated chapter, with the flood zone definitions, the vulnerability rules and the sequential and exception tests brought together in one place. For most applicants the practical changes are these.

• The FRA is now a named national requirement. A site-specific assessment is listed as national information that has to be submitted, so a missing or thin report is a firmer reason to reject the application at validation.
• More sites are caught. The trigger for an assessment in Flood Zone 1 has been broadened to any land the maps show at risk from any source, which pulls in surface water sites that used to slip through.
• Surface water can now be handled without a sequential test. Where a site is at risk from surface water only, the test can fall away if the assessment shows clearly that the design keeps people safe for the development’s lifetime. The report has to carry that argument, so the surface water chapter now does work the sequential test used to do.
• The wording is firmer. The safety and compatibility policies are now framed as refusal unless the tests are met, rather than permission where they are, which raises the bar the evidence has to clear.
• Drainage standards are mandatory. Sustainable drainage now has to be designed to the 2025 National Standards for SuDS, and that applies to minor schemes as well as major ones.

A report written to the old paragraph numbers now looks out of date on the case officer’s desk, and out-of-date evidence is the quickest way to lose time on an application.

None of this changes what a well-prepared assessment sets out to do; it raises the standard the evidence has to meet. For the full policy detail, our NPPF flood risk guidance walks through the new chapter, and the changes for flood risk and drainage are covered in more depth on our blog. Sites in Wales continue to follow TAN15 guidance.

What does a flood risk assessment involve?

A sound assessment is more than a map printout. It works through each relevant source of flooding, tests the design against it, and shows the residual risk is safe and not made worse elsewhere. The work usually covers the following ground.

• Every source that applies. Rivers, the sea, surface water, groundwater, sewers and reservoirs, weighted to what actually threatens the site.
• Flood levels and depths. Using Environment Agency data and, where levels are marginal or disputed, our own hydraulic modelling.
• Climate change over the development’s life. Applying the current climate change allowances so the scheme is safe decades from now, not just today.
• Layout, levels and mitigation. Finished floor levels, safe access and egress, flood resistance and resilience, and compensatory storage where floodplain is affected.
• Surface water and drainage. How runoff is managed, tied to a sustainable drainage strategy designed to the national standards. Many schemes need both an FRA and a drainage strategy.

Flood zones, the flood map and your site

England’s flood zones describe how likely river and sea flooding is across an area, and they are the starting point for whether an assessment is needed and what it must show. Zone 1 is low probability, Zone 2 is medium, and Zone 3 is high, split into 3a and the functional floodplain at 3b. Our guide to the flood zones explained sets out what each one means for development.

The zones you see on the Flood Map for Planning do not account for defences or for climate change, which is why a site-specific assessment reads behind the headline zone. The map was updated in May 2026 to add surface water climate change extents and banded depth data, and that data is now part of the formal evidence base for the tests. The Environment Agency’s check your long-term flood risk service and the national planning practice guidance sit alongside it.

A quick way to see where your site stands is our free flood risk map postcode checker, though a mapped flag is the beginning of the conversation, not the end of it.

What is in your flood risk assessment report

Every Unda assessment is written to be read by the people who decide the application, and to stand up if it is looked at again later. A typical report includes:

• A clear risk conclusion. What the flood risk to the site is, from each source, in plain terms a non-specialist can follow.
• The policy case. How the scheme meets the sequential and exception tests where they apply, and the safety and drainage requirements of the current Framework.
• Design and mitigation measures. Finished levels, access and egress, resistance and resilience, and how surface water is managed.
• Evidence and data sources. The maps, modelling and allowances the conclusions rest on, referenced so a consultee can check them.
• A report that lasts. Because permitted homes are increasingly looked at again by lenders and insurers, we write the assessment to hold up at conveyancing and underwriting, not only at the planning counter.

How much does a flood risk assessment cost?

There is no single price, because an assessment is scoped to the site. A small extension in Flood Zone 1 with a clear surface water picture is a different piece of work from a housing scheme in Flood Zone 3 that needs modelling and a sequential test. The honest answer is that the fee follows the work the planning position demands.

• The flood zone and sources involved. More sources and higher risk mean more analysis.
• Whether modelling is needed. Bespoke hydraulic modelling to settle a disputed level costs more than a desk-based review.
• The size and type of development. Scale, vulnerability and any change of use all move the scope.
• Accompanying reports. A sequential test or a drainage strategy alongside the FRA adds to the picture.

We explain the drivers, and why a bespoke report tends to serve an application better than a fixed-price template, in our guide to what a flood risk assessment costs. The quickest way to a real number is to ask us: send the address and we will price it.

Why choose Unda as your flood risk assessment consultants

Unda is a specialist flood risk and drainage consultancy, not a general engineering practice with a flooding sideline. That focus shows in reports that get through planning, and in the way we deal with the Environment Agency and lead local flood authorities when they raise queries.

• Chartered consultants. We are a CIWEM Business Partner and every assessment is signed off by a chartered flood risk consultant.
• Independent advice. We are not tied to a developer or an insurer, so the conclusion is the one the evidence supports.
• Built for the current policy. Reports are written to the August 2026 Framework and the national drainage standards, so they read as current on the officer’s desk.
• We handle the objections. If a consultee raises a flood risk objection, we respond to it rather than leaving you to.
• Rated 5.0 on Google. Developers, planning consultants and homeowners come back to us because the reports do their job. Here is why that expertise matters.

Local knowledge across England and Wales

Flood risk is local. The river that threatens a site, the authority that determines the application and the data that describes the risk all change from place to place, and a report that reads the local picture carries more weight than a generic one. We work nationwide and hold detailed knowledge of the catchments and authorities behind that coverage.

• By area. Flood risk assessments town by town and county by county.
• By river. The flood behaviour of watercourses river by river.
• By authority. What each local planning authority and lead local flood authority expects.

Flood risk assessment FAQs

Speak to our flood risk assessment consultants

If you have been asked for a flood risk assessment, or you are not sure whether you need one, talk to us before the deadline gets close. Our experienced consultants will tell you which report the authority will accept, what it will cost, and how quickly we can turn it round. Call +44 (0) 1293 214444 or email enquiries@unda.co.uk, and we will take it from there.