Flood risk assessment and SuDS compliance

Why flood risk matters for your development

Flood risk is a significant planning constraint in England and Wales. If you're developing land or changing the use of property, you need to understand how flood risk affects your project and what assessments or approvals you'll need.

The regulatory position differs dramatically between England and Wales on sustainable drainage. In Wales, SuDS approval is mandatory — building without it exposes you to enforcement and stop notices, and failing to comply with a notice is a criminal offence. In England, SuDS remains voluntary at national level, though many local planning authorities require it through planning conditions.

Getting flood risk wrong can be costly. Planning applications may be refused, developments may be uninsurable, and in Wales you face enforcement action and potential prosecution for non-compliance with SuDS requirements.

Flood Zones explained

The Environment Agency classifies land into Flood Zones based on the probability of flooding. Your development site's flood zone determines what assessments you need and whether your proposed use is appropriate.

When you need a Flood Risk Assessment

A site-specific Flood Risk Assessment (FRA) is a detailed study that identifies flood risks to your development and proposes mitigation measures. It must be prepared by a competent professional with appropriate qualifications.

FRA is required for

• All development in Flood Zones 2 and 3, regardless of size
• Development of 1 hectare or more in Flood Zone 1
• Any site with known critical drainage problems
• Development that may increase flood risk elsewhere

Even if your site is in Flood Zone 1, check with your local planning authority whether an FRA is needed. Some areas have localised flood risks from surface water, groundwater, or ordinary watercourses that aren't reflected in the main flood zone maps.

What an FRA must include

• Assessment of all sources of flood risk (river, sea, surface water, groundwater, sewers)
• Climate change allowances applied to flood levels
• How the development will be safe throughout its lifetime
• How the development will not increase flood risk elsewhere
• Proposed mitigation measures (finished floor levels, flood-resistant construction, safe access and egress)

Sequential and Exception Tests

If you want to develop in Flood Zones 2 or 3, you may need to pass the Sequential Test and possibly the Exception Test before your planning application can be approved.

Passing the Sequential Test

You must demonstrate that there are no reasonably available sites at lower flood risk where your development could be located. This means searching for alternative sites in Flood Zone 1, then Flood Zone 2, before accepting a site in Flood Zone 3.

The search area depends on your development type. For a local convenience store, you might only need to search within your target neighbourhood. For a regional warehouse, you'd need to search a wider area.

When the Exception Test applies

If you pass the Sequential Test but still propose development in Flood Zone 3a, you may also need to pass the Exception Test. This requires demonstrating:

1. The development provides wider sustainability benefits to the community that outweigh flood risk
2. The development will be safe for its lifetime, will not increase flood risk elsewhere, and will reduce risk overall where possible

Both parts must be satisfied. The Exception Test is rigorous and not all proposals will pass.

Wales: Mandatory SuDS requirements

If you're developing in Wales, you must obtain SuDS Approval Body (SAB) approval before construction begins. This applies to all developments meeting the threshold, regardless of whether planning permission is required.

The SAB approval process

The SuDS Approval Body is your local authority's designated team for assessing drainage applications. The process runs parallel to planning permission but is a separate approval.

Wales SAB fees

SAB applications incur fees based on construction area size, plus inspection fees where conditions are attached.

Wales: Criminal penalties for non-compliance

Unlike England, non-compliance with the SuDS regime in Wales can become a criminal matter, not just a planning enforcement issue. The offence is failing to comply with a SAB temporary stop notice, stop notice or enforcement notice, and it carries an unlimited fine.

Flood insurance considerations

Flood risk affects your ability to insure property. This matters both during development and for future occupiers or purchasers.

Flood Re scheme

The government-backed Flood Re scheme helps households in high flood risk areas obtain affordable insurance. However, it has significant limitations for business development.

Insurance implications for businesses

Flood Re does not cover commercial properties. If you're developing business premises in a flood risk area, you must consider:

• Commercial flood insurance availability - May be expensive, have high excesses, or be unavailable for high-risk locations
• Future saleability - Properties that are uninsurable or have prohibitive insurance costs are harder to sell or let
• Lender requirements - Banks typically require flood insurance as a condition of commercial mortgages
• Business continuity - Even with insurance, flood events cause significant business disruption

Properties built after 1 January 2009

Flood Re excludes properties built after 1 January 2009. This deliberate exclusion encourages flood-resistant construction in new developments. If you're building new residential property in a flood risk area, future occupiers will need to obtain insurance on the open market without Flood Re support.

This makes it even more important to incorporate robust flood mitigation measures in new developments, both to obtain planning permission and to ensure future insurability.

Climate change considerations

Flood Risk Assessments must account for climate change. The Environment Agency publishes climate change allowances that must be applied to flood levels when assessing risk and designing mitigation.

What climate change means for your development

• Higher flood levels - Peak river flows and sea levels will increase over the development's lifetime
• More intense rainfall - Surface water flooding becomes more likely and severe
• Lifetime assessment - Residential development typically assessed over 100 years, commercial over 60 years
• Adaptive design - Consider how the development could be adapted if flood risk increases beyond predictions

The allowances are updated periodically. Use the latest Environment Agency guidance when commissioning your FRA.

Practical tips for development in flood risk areas

Site selection

• Check the Environment Agency's flood maps early in site selection
• Request pre-application advice from the local planning authority
• Consider whether the Sequential Test can realistically be passed
• Factor FRA and SuDS costs into your development appraisal

Design considerations

• Raise finished floor levels above flood levels (with climate change allowance)
• Consider flood-resistant construction (water-resistant materials, raised electrics)
• Ensure safe access and egress routes during flood events
• Design SuDS to provide multiple benefits (attenuation, water quality, amenity, biodiversity)

Cross-border projects

If you work across England and Wales, remember:

• Wales: SuDS approval mandatory, enforcement notices with criminal sanctions if you build without approval, separate SAB application
• England: SuDS through planning conditions, no separate approval body, no criminal penalty

Do not assume that experience in one nation applies to the other.

Environment Agency consultation

The Environment Agency (EA) is a statutory consultee for planning applications in flood risk areas. Their response carries significant weight with planning authorities.

When EA must be consulted

• All applications in Flood Zones 2 and 3
• Development of 1 hectare or more in Flood Zone 1
• Applications within 20 metres of a main river
• Development in an area with critical drainage problems

EA objections

If the EA objects to your application on flood risk grounds, the planning authority should not approve it unless there are exceptional circumstances. If they do approve despite EA objection, the application is referred to the Secretary of State who can call it in for decision.

Addressing EA concerns early in the process is essential. Consider pre-application discussions with EA as well as the planning authority.