Flood Risk Assessment for Planning

A flood risk assessment for planning is the technical report a local planning authority needs before it can grant permission on a site where flooding is a concern. Unda prepares these assessments for development sites across England, giving planning officers the evidence they need to determine an application and giving developers a clear route through what can be a frustrating part of the process.

We work with developers, architects and planning consultants on residential, commercial and mixed-use schemes. Our flood risk consultants read the flood risk affecting a site, set out how the development stays safe for its lifetime, and write it up in a report that answers the questions a planning officer and the Environment Agency will ask.

Unda is a CIWEM Business Partner, and our team includes CIWEM Chartered consultants, so your assessment is prepared and checked by qualified flood risk specialists. Clients rate us 5.0 on Google.

The aim is simple: a submission that holds up first time, scoped to the actual risk rather than padded out.

What is a flood risk assessment for planning?

A flood risk assessment for planning (an FRA) is a site-specific technical report submitted with a planning application. It identifies every source of flooding that could affect the site, judges how those risks bear on the proposed development, and demonstrates that the scheme can be built and used safely for its lifetime without increasing flood risk elsewhere.

Flood risk is a material consideration in the English planning system. Authorities must steer development towards land at the lowest probability of flooding and, where a site carries risk, must see the evidence before they approve it. That evidence is the FRA, prepared in line with the National Planning Policy Framework and the Planning Practice Guidance on flood risk and coastal change. Our NPPF flood risk guidance explains how these policies apply to a development site. Schemes in Wales sit under a different framework and normally need a Flood Consequence Assessment instead.

When is a flood risk assessment required for a planning application?

Whether your application needs an FRA depends on where the site is, how big and how vulnerable the proposed use is, and what the national and local flood evidence shows. The Environment Agency's standing advice and the Planning Practice Guidance set out the triggers. In most cases the trigger is the flood zone the site sits in, but size and surface water risk pull sites in Flood Zone 1 into scope too.

Set out in full, the Environment Agency guidance identifies these situations where a site-specific flood risk report for planning should normally be prepared.

Flood zones are read from the Environment Agency Flood Map for Planning, and local authorities lean on their Strategic Flood Risk Assessments to understand risk across their patch. Surface water is now the single largest source of flood risk in England, with around 4.6 million properties exposed, which is why a low-lying Zone 1 site can still need assessment. If an FRA is required and you don't submit one, the authority can refuse the application outright or hold it until the technical evidence arrives.

The quickest way to see whether your site is affected is to check the flood zone first. Our free flood risk map postcode checker shows the Environment Agency flood zones for any location in England in seconds, and our guide to when an FRA is required works through the Flood Zone 1 triggers in more detail.

Flood zones explained

The flood zones drive how a proposal is judged under planning policy. In short: Flood Zone 1 is land with a low probability of river or sea flooding, where most development is acceptable but size and surface water risk can still trigger an FRA; Flood Zone 2 is medium probability, where an FRA is normally needed; Flood Zone 3a is high probability, where an FRA is needed and the Sequential Test usually applies; and Flood Zone 3b is the functional floodplain, where water has to flow or be stored in a flood and development is heavily restricted.

The zones on the Flood Map for Planning ignore existing defences, which is why a site behind a flood wall can still show in Zone 3. Reading what that means for a specific scheme is a core part of the assessment, and our flood zones explained guide sets out each one in full.

What a flood risk assessment for planning needs to cover

An FRA has to give the authority enough to be sure flood risk has been designed for properly and that the site will be safe for its intended use throughout its life. Depending on the site, that normally means assessing:

• Rivers and the sea. Fluvial and tidal flood risk affecting the site.
• Surface water. Pluvial flooding from rainfall that overwhelms the ground and drainage.
• Groundwater. Rising water tables, more common on some geologies than others.
• Infrastructure sources. Flooding from reservoirs, canals and other artificial sources.
• Climate change. The Environment Agency allowances applied over the development's lifetime.
• Effect on others. Whether the development would increase flood risk elsewhere.
• Mitigation and design. The measures needed to make the scheme safe, including finished floor levels.

For many sites the analysis is proportionate and straightforward. Where a site sits close to a watercourse or flood defence, or where flood levels aren't already established, the FRA may need to be underpinned by flood modelling. And where policy requires it, the assessment is accompanied by Sequential and Exception Test reporting, the tests that decide whether a site is appropriate for development at all. These policy tests, and how the wider framework applies, are set out in our NPPF flood risk guidance for planning. Climate change is not optional here: the FRA must apply the Environment Agency's climate change allowances so the scheme is shown to stay safe over its whole lifetime.

How flood risk affects a planning decision

Flood risk can be the thing that decides an application. Because it's a material consideration, an authority must be satisfied the site is in the right place and designed to stay safe before it grants permission. Where risk may be significant, it will usually consult the Environment Agency as a statutory consultee, and those comments carry real weight. The Agency responded to more than 9,600 planning consultations in 2024-25 against a 21-day statutory target, so building the timeline around that consultation matters.

If flood risk hasn't been addressed properly, an authority may:

• Ask for more evidence. Requesting additional technical work before it will determine the application.
• Require design changes. Sending the scheme back for finished floor levels, layout or mitigation to be revised.
• Receive objections. From the Environment Agency, the lead local flood authority or other consultees.
• Delay the decision. Holding determination while the flood risk position is resolved.
• Refuse permission. Where the risk hasn't been shown to be acceptable.

Flood risk also runs into drainage: many schemes have to show how surface water runoff will be managed through a sustainable drainage system, set out in a surface water drainage strategy. Several bodies share responsibility for flood risk in the planning system, from the Environment Agency to the lead local flood authority, and our guide to who manages flood risk in England explains how they fit together. Aviva's research found around one in nine new homes built recently in England sits in a medium or high flood risk area, and authorities are scrutinising flood risk more closely as a result.

Is a flood risk assessment for planning the right report for you?

Not every flood risk question is answered by a planning FRA. If you've landed here but your situation is one of these, here's where to go:

• Your site is in Wales. Welsh applications follow TAN15 and normally need a Flood Consequence Assessment, not an FRA.
• You need to justify the site's location. Policy may require Sequential and Exception Tests before permission can be granted.
• You're buying a home and worried about flooding. A homebuyer flood risk survey is the report you want, not a planning FRA.
• You need flood cover for an existing property. An insurance flood risk assessment is the right document.
• Your site needs detailed flood levels. Complex sites often need hydraulic flood modelling to establish levels and behaviour.
• You're chasing a BREEAM credit. Our BREEAM flood risk assessment covers the relevant requirements.
• Your issue is really drainage. A preliminary drainage design or SuDS strategy may be what the authority is asking for.

Not sure which applies? Tell us about the site and we'll point you to the right assessment, with no obligation. You can also browse our full flood risk assessment services to see the whole range.

What's in an Unda planning flood risk assessment report

Every report is written for the people who will actually read it: the planning officer and, where relevant, the Environment Agency. A typical Unda planning FRA sets out the development and its planning context, the flood zone and risk classification, an assessment of each relevant flood source, the climate change allowances applied, finished floor levels and any other mitigation, the effect on flood risk elsewhere, and a clear conclusion on whether the scheme is safe and policy-compliant. It's concise, evidenced and structured the way authorities expect, rather than a box-ticking template.

What does a flood risk assessment for planning cost?

There's no single price, because the work scales with the site. The main drivers are:

• The flood zone and sources in play. A Zone 1 surface water flag is a very different job from a main-river Zone 3 site.
• The size and vulnerability of the development. A single dwelling sits at one end; a large mixed-use scheme at the other.
• Whether the policy tests apply. Sequential and Exception Test work adds scope where it's required.
• Whether flood modelling is needed. Establishing flood levels hydraulically is a significant piece of work in its own right.

We scope each quote to the actual risk so you're not paying for analysis your site doesn't need. For a fuller breakdown of what moves the price, see our guide to how much a flood risk assessment costs.

Our approach to preparing flood risk assessments

Our process is built to give proportionate, defensible evidence without dragging out the programme.

1. Review the site and its planning context. Understanding the proposal, its location and the policy that applies.
2. Analyse the flood data. The Flood Map for Planning, the local SFRA and available flood risk information.
3. Assess the risk. Judging the flood risk affecting the site from each relevant source.
4. Identify mitigation. Setting out the design measures needed to make the development safe.
5. Prepare the report. A clear, concise FRA ready for planning submission.

Getting a flood risk consultant involved early, before the application goes in, often surfaces issues while they're still cheap to fix, and keeps flood risk from becoming the reason a decision slips. Our step-by-step guide on how to do a flood risk assessment explains the process in more depth.

Why developers and planning consultants choose Unda

Flood risk can stall or sink an application when it's handled badly. Clients come to Unda because we keep it moving:

• Chartered, accredited expertise. Unda is a CIWEM Business Partner and our team includes CIWEM Chartered consultants, so your assessment is prepared by qualified flood risk specialists.
• Consultants who know the policy. Direct working knowledge of the Environment Agency's flood risk standing advice and NPPF requirements, so the report answers the right questions.
• Scope matched to the risk. Proportionate analysis sized to your site, without unnecessary work or cost.
• A clear reading of planning. We translate policy into what your application actually has to show.
• Joined up with the wider work. Coordinated with SuDS strategies, Sequential and Exception Tests and flood modelling where they're required.
• Reports built for submission. Concise, evidenced and ready to go in.

We also carry local knowledge across England. Our area flood risk pages, river flood risk pages and local authority guides cover the requirements that vary from council to council, and our live river levels map shows current conditions on watercourses near a site.

FRA for planning: common questions

If your development proposal needs a flood risk assessment, our experienced consultants can review the site, advise on the right scope, and prepare a report ready for submission. Call +44 (0) 1293 214444, email enquiries@unda.co.uk, or request a quote and we'll come back to you within 60 minutes.