Flood Risk Assessment
A Flood Risk Assessment is one of the most frequently required documents for planning applications across England and Wales. With over 5 million properties at risk of flooding in the UK, local authorities take flood risk extremely seriously when deciding planning applications.
Typical Cost
£300 – £5,000+
Turnaround
1 – 6 weeks
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What is a Flood Risk Assessment?
A Flood Risk Assessment (FRA) evaluates the likelihood of a proposed development being affected by flooding from rivers, the sea, surface water, groundwater, or sewers. It also considers whether the development could increase flood risk to neighbouring properties or the wider area. The assessment draws on Environment Agency flood maps, historical flood data, site-specific surveys, and hydrological modelling to build a complete picture of flood risk at the site.
When is a Flood Risk Assessment required?
You will need a Flood Risk Assessment if your site falls within Flood Zone 2 or Flood Zone 3 on the Environment Agency flood maps. Sites in Flood Zone 1 also require an FRA if the development area exceeds 1 hectare, or if the council has identified local flooding issues in that area. Most local authorities now request at least a basic flood risk statement for any application involving new residential units, regardless of flood zone. Check your council's validation checklist to be certain.
What does a Flood Risk Assessment include?
A thorough FRA will include a description of the site and its surroundings, an assessment of all sources of flood risk, details of existing drainage infrastructure, proposed mitigation measures such as raised floor levels or flood-resilient construction, surface water management proposals, and an emergency flood plan showing safe access and egress routes during a flood event.
How much does a Flood Risk Assessment cost?
The cost of a Flood Risk Assessment varies depending on the complexity of the site and the level of detail required. A straightforward desktop FRA for a small residential site in Flood Zone 1 typically costs between £300 and £600. A full site-specific FRA involving hydraulic modelling for a development in Flood Zone 3 can range from £1,500 to £5,000 or more. Major developments with complex watercourse interactions may require assessments costing upwards of £10,000.
Who can prepare a Flood Risk Assessment?
Flood Risk Assessments should be prepared by a suitably qualified professional, usually a chartered civil engineer, hydrologist, or environmental consultant with specific expertise in flood risk management. Many firms specialising in FRAs hold membership of the Chartered Institution of Water and Environmental Management (CIWEM). While there is no strict legal requirement for specific qualifications, local planning authorities and the Environment Agency will scrutinise the competence of the assessor.
How long does a Flood Risk Assessment take?
A desktop-based FRA for a simple site can usually be completed within 5 to 10 working days. More detailed assessments involving site visits, topographic surveys, and hydraulic modelling typically take 3 to 6 weeks. If Environment Agency consultation is needed, add an additional 21 days for their statutory response period.
Frequently Asked Questions
Do I need a Flood Risk Assessment for a house extension?
You may need one if your property falls within Flood Zone 2 or 3. Extensions in Flood Zone 1 generally do not require an FRA unless the site has a history of localised flooding or the total site area exceeds 1 hectare. Check the Environment Agency's Flood Map for Planning to find your flood zone.
How do I find out what flood zone my property is in?
Visit the Environment Agency's Flood Map for Planning service at flood-map-for-planning.service.gov.uk. Enter your postcode or site address, and the map will show whether your property falls within Flood Zone 1 (low risk), Flood Zone 2 (medium risk), or Flood Zone 3 (high risk).
Can I write my own Flood Risk Assessment?
While there is no legal requirement to hire a professional, preparing your own FRA is not recommended. Local planning authorities expect a certain standard of technical analysis, and a poorly prepared assessment is likely to be rejected, delaying your application. The Environment Agency also reviews FRAs for major applications and will flag inadequate assessments.
What happens if my Flood Risk Assessment fails?
If your FRA identifies significant flood risk that cannot be adequately mitigated, the planning authority may refuse your application. However, most FRAs identify risks alongside workable mitigation measures, such as raising finished floor levels, installing flood barriers, or improving site drainage. The goal is to demonstrate that risk can be managed to acceptable levels.
How long is a Flood Risk Assessment valid for?
There is no fixed expiry date, but an FRA is generally considered valid for 12 to 24 months. If flood maps are updated, new climate change allowances are published, or significant changes occur upstream, your FRA may need refreshing. Planning authorities may request an updated assessment if substantial time has passed since the original was prepared.
What is the difference between Flood Zone 2 and Flood Zone 3?
Flood Zone 2 covers areas with a medium probability of flooding, meaning there is between a 0.1% and 1% annual chance of river flooding, or between 0.1% and 0.5% annual chance of sea flooding. Flood Zone 3 covers areas with a high probability, where the annual chance of river flooding exceeds 1%, or sea flooding exceeds 0.5%.
Does a Flood Risk Assessment cover surface water flooding?
Yes. A comprehensive FRA should assess all sources of flood risk including rivers, the sea, surface water runoff, groundwater, sewers, and reservoirs. Surface water flooding is increasingly recognised as a major risk, particularly in urban areas where heavy rainfall overwhelms drainage systems.
Do I need to pass the Sequential Test as well as having an FRA?
If your site is in Flood Zone 2 or 3, the planning authority must apply the Sequential Test to determine whether there are reasonably available alternative sites at lower flood risk. This is a separate requirement from the FRA itself. For some applications, you may also need to pass the Exception Test, which requires demonstrating wider sustainability benefits.
Will the Environment Agency review my Flood Risk Assessment?
The Environment Agency is a statutory consultee for planning applications in Flood Zone 2 and 3, and for major developments in Flood Zone 1. They will review your FRA and provide comments to the local planning authority. For minor applications in lower flood zones, the council's own drainage officer typically reviews the assessment.
Can a Flood Risk Assessment increase my insurance premiums?
The FRA itself does not directly affect insurance premiums. However, the flood risk information it contains may already be known to insurers through Environment Agency data. In practice, having a good FRA with effective mitigation measures in place can actually help when negotiating insurance terms, as it demonstrates the risk has been properly assessed and managed.