Flood Risk Assessments for Homes & Small Developments
Planning an extension, loft conversion, or small development? If your site is in a flood zone, you'll likely need a flood risk assessment for planning permission. We make the process simple, fast, and affordable.
When is a flood risk assessment required?
Not every project needs an FRA. Here are the most common triggers — if any of these apply, you almost certainly need one.
Your site is in Flood Zone 2 or 3
Check the Environment Agency's Flood Map for Planning. If your site is shown in Flood Zone 2 (medium probability) or Flood Zone 3 (high probability), an FRA is required for any development.
Your development is over 1 hectare in Flood Zone 1
Even in the lowest-risk flood zone, sites over 1 hectare require an FRA because of their potential impact on surface water drainage.
You're changing the use to residential
Converting a commercial property, barn, or other non-residential building to a dwelling is classed as 'more vulnerable' development and triggers an FRA in flood zones.
Your council has identified local flood risk
Some local planning authorities require FRAs for areas with known surface water, groundwater, or sewer flood risk — even in Flood Zone 1. Your planning officer or pre-application advice will confirm this.
Your extension is in a Critical Drainage Area
Some London boroughs and other councils have designated Critical Drainage Areas where any development, including extensions, requires a flood risk assessment.
FRAs for every residential scenario
House Extension
Rear, side, and wraparound extensions. Classified as minor development — typically requires a desktop FRA with flood mitigation measures and finished floor level recommendations.
Loft Conversion
Loft conversions that create a new habitable floor. The FRA addresses safe refuge, flood warning, and evacuation — key concerns when adding bedrooms above flood level.
New Build (1-4 Units)
Small residential developments including single dwellings, semi-detached pairs, and small clusters. May require the Sequential Test and Exception Test depending on flood zone and vulnerability.
Change of Use
Converting offices, barns, pubs, or shops to residential. This increases flood vulnerability classification, so even Flood Zone 2 sites need to demonstrate safety through the Exception Test.
Permitted Development
Some permitted development rights still require a flood risk assessment — particularly larger home extensions and agricultural-to-residential conversions under Class Q.
Four steps to your flood risk assessment
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Check your flood zone
We check the Environment Agency flood maps and local data to determine your exact flood risk. You can also use our free flood risk check tool.
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Tell us about your project
Share your site address, development type, and any planning documents you have. We'll confirm exactly what type of FRA you need and send you a fixed-fee quote.
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We deliver your FRA
Our chartered engineers prepare your flood risk assessment, including flood zone analysis, risk assessment, mitigation strategy, and planning policy compliance.
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Submit with your planning application
You receive a planning-ready PDF report to submit directly to your local planning authority alongside your application drawings and forms.
Why homeowners and small developers choose us
- Fixed-fee pricing — no hourly rates or hidden charges
- 5-10 working day turnaround on most residential FRAs
- Every report reviewed by a Chartered Civil Engineer
- Plain-English reports your council will accept first time
- 640+ flood risk assessments delivered across England and Wales
- Free initial consultation to confirm whether you need an FRA
Not sure if you need an FRA?
Use our free flood risk check tool to find out in 60 seconds, or call us on 020 8156 6076 for a free 5-minute consultation. We'll tell you honestly whether you need one.
Map your site in minutes.
Draw your site boundary on our interactive map and get an instant constraint assessment — including flood zones, surface water risk, and other planning constraints.
Map Your Site NowWhy map my site?
- Instant flood zone identification
- Surface water and other risk layers
- Helps us scope your FRA accurately
- Speeds up your quote turnaround
Frequently asked questions
- How much does a residential flood risk assessment cost?
- Costs vary depending on the flood zone, development type, and whether you need a desktop study or detailed assessment. Most residential FRAs for extensions and small developments are competitively priced with fixed fees. We'll confirm the exact cost in your quote — no surprises.
- What is the difference between a desktop FRA and a detailed FRA?
- A desktop FRA uses existing flood data, maps, and modelling to assess risk — suitable for most extensions, loft conversions, and minor works. A detailed FRA may include site-specific hydraulic modelling and is typically required for new builds in Flood Zone 3 or sites with complex flood mechanisms.
- Can I get planning permission in a flood zone?
- Yes. Thousands of planning permissions are granted every year for sites in Flood Zones 2 and 3. The key is providing a robust FRA that demonstrates the development will be safe for its lifetime and will not increase flood risk elsewhere. We design the mitigation strategy to meet these requirements.
- Do I need a flood risk assessment for a single-storey extension?
- If your property is in Flood Zone 2 or 3, yes. Extensions are classified as minor development under national planning policy, but they still require an FRA in medium and high-risk flood zones. The good news is that extension FRAs are relatively straightforward and affordable.
- How long does a flood risk assessment take?
- Most desktop FRAs are completed within 5-10 working days from receiving all necessary information. Detailed assessments with hydraulic modelling may take 2-4 weeks. We'll confirm the timeline when we send your quote, and we can accommodate urgent deadlines where possible.
- Will the Environment Agency object to my extension?
- For minor development like extensions, the Environment Agency is rarely a statutory consultee. However, for new builds and changes of use in Flood Zone 3, the EA will be consulted. Our FRAs are designed to address the EA's standard requirements, and we have a strong track record of receiving 'no objection' responses.
- Can I write my own flood risk assessment?
- Technically, there is no legal requirement for an FRA to be written by a qualified professional for minor works. However, planning authorities expect FRAs to be technically robust and will reject inadequate reports. Most homeowners find it far more cost-effective to commission a professional FRA than risk delays and resubmissions.
- What happens after I submit my enquiry?
- We review your details and check your flood zone within one business day. You'll receive a fixed-fee quote by email, with a clear scope of work, timeline, and what's included. There is no obligation — if you decide not to proceed, that is fine.