Flood Risk Assessment in London & the UK

Usually, yes. If your site is in Flood Zone 2 or 3, you need an FRA even if it is protected by defences. The council will want to know what would happen if a defence was breached or overtopped. This is called residual risk, and it often decides your finished floor levels and where bedrooms can go.

Often, yes, even in Flood Zone 1. Basements are the most vulnerable part of a building to surface water and sewer flooding. Most London boroughs expect a flood risk assessment or basement impact assessment that covers surface water depth, sewer flooding protection, groundwater and safe access.

It is a standard form used across London to summarise how a development will manage rainwater. It covers the site, the London Plan drainage hierarchy, run-off rates and storage volumes. Many boroughs ask for it with planning applications. We complete it as part of our drainage strategy.

Your borough decides the planning application. Its flood team, as Lead Local Flood Authority, reviews surface water and drainage. The Environment Agency is consulted on river and tidal flood risk, mainly for sites in Flood Zones 2 and 3.

Flood risk now has its own chapter (Chapter 18). The main changes are: sustainable drainage is required on all development, designed to the National Standards for Sustainable Drainage Systems; sites at risk from surface water only can be exempt from the Sequential Test if the FRA shows the development will be safe; and the Exception Test now applies only to river and sea flooding. Applications decided after August 2026 must meet the new policy.

In the UK, you generally need an FRA if your project is in Flood Zone 2 or 3, or if it’s over 1 hectare in Flood Zone 1. At Enviropass, we provide a rapid screening service to determine exactly what the Environment Agency or Lead Local Flood Authority requires, saving you from unnecessary delays.

Our Flood Risk Assessments start from £850 + VAT. The final price depends on the flood zone, the size of the site and the type of development. For example, a house extension costs less than a multi-unit or commercial scheme. We give you a fixed-fee quote before we start, so there are no hidden costs.

Typically, we deliver a comprehensive report within 5 to 10 working days. If you're facing a tight planning deadline, our team works efficiently to ensure your submission remains on track.

Usually just a site location plan and your proposed layout. We handle the rest, including sourcing data from the Environment Agency and local authorities.

For very simple, low-risk projects, such as a small house extension, GOV.UK says you may be able to prepare the assessment yourself using the Environment Agency's standing advice. For most other projects, including new homes, conversions, basements and anything in Flood Zone 3, a specialist report is the safer choice. It must assess all sources of flooding, apply the Sequential Test where needed and meet your council's requirements. If the FRA is not good enough, the council can refuse your application.

Flood Zone 2 represents a medium probability of flooding, while Zone 3 is high probability. Both require professional assessments. We specialise in finding viable engineering solutions to make developments in these zones safe and "approvable."

It is possible, but the hurdles are high. You need a top-tier Flood Risk Assessment and a strong mitigation strategy. Enviropass has a proven track record of helping clients navigate the complexities of Zone 3 developments.

These terms come from older guidance and describe increasing levels of detail: Level 1 is a screening study, Level 2 is a scoping study and Level 3 is a detailed assessment, sometimes with flood modelling. Today, planning guidance simply asks for a site-specific FRA that is proportionate to the risk. Councils also publish Level 1 and Level 2 Strategic Flood Risk Assessments, which are area-wide studies, not reports for individual sites. When we quote, we will tell you what level of detail your site needs.

The Sequential Test aims to steer development to areas with the lowest risk of flooding. We help developers justify their site choice by providing the robust data and comparative analysis that planning officers look for.

If a project provides wider sustainability benefits but is in a high-risk area, it must pass the Exception Test. We provide the expert technical backing to prove the development will be safe and won't increase risk elsewhere.

This is flooding caused by heavy rainfall rather than overflowing rivers. It’s a major focus for UK planners. Our combined FRA and SuDS services address both river and surface water risks simultaneously.

A Critical Drainage Area (CDA) is an area with known drainage problems, usually surface water flooding after heavy rain. If your site is in a CDA, you will usually need a Flood Risk Assessment even if it is in Flood Zone 1, and the council will expect a detailed drainage strategy.

UK regulations require "climate change allowances" to be factored into flood levels. We use the latest 2024 Environment Agency projections to ensure your development remains safe for its entire lifetime.

This is the risk remaining after mitigation (like flood barriers) is in place. We help you manage this through robust emergency flood plans, which are often a condition of planning.

Often, yes. If you are changing a commercial building to residential in a flood zone, the "vulnerability classification" changes, making an FRA mandatory. We specialise in these types of conversions.

Basements are considered "highly vulnerable." You will need a very specific Flood Risk Assessment to prove safety and dry egress. We can help you determine if your basement project is viable.

Yes. Objections often arise from a lack of clarity. We provide the detailed hydraulic evidence and mitigation strategies needed to satisfy the Environment Agency and move your application forward.

Refusal often stems from insufficient data or poor mitigation plans. Enviropass can review your refusal, update your Flood Risk Assessment with better evidence, and support your appeal or re-submission.

Definitely. A "pre-app" flood risk review from Enviropass can save you from buying a site that is undevelopable. It’s an essential part of due diligence for any developer.

An FRA looks at water coming onto your site; a Drainage Strategy (SuDS) looks at water leaving your site. Most UK developments now require both, and we offer them as a streamlined package.

A Sustainable Drainage Systems (SuDS) assessment outlines how surface water will be managed to prevent flooding elsewhere. Since August 2026, national planning policy requires sustainable drainage on all development, not just major schemes, so councils are increasingly asking for one on smaller sites too.

Local authorities are tightening rules to combat urban runoff. Even small infill projects can impact local drainage. Our SuDS reports are scaled to your project size, ensuring you aren't over-engineering but still meeting every local requirement.

Yes, our SuDS assessments provide the strategy and conceptual design needed for planning approval, including calculations for rainfall runoff and storage volumes.

It’s a sequence of preferred discharge points: first infiltration (into the ground), then a watercourse, and finally a sewer. We perform the necessary checks to see which stage of the hierarchy your site can achieve.

The LLFA (usually the County or Unitary Council) reviews your SuDS strategy. We maintain professional relationships with LLFAs across the UK to ensure our reports align with their specific local preferences.

Planners often require that your new development doesn't shed water faster than an empty field would. We use industry-standard software to calculate these rates and design your SuDS accordingly.

If you plan to use infiltration, a BRE 365 soakaway test is often required. Enviropass can coordinate this data into your final report to prove your drainage strategy is grounded in physical reality.

Yes. While infiltration might not work, we design "attenuation" systems that store water and release it slowly. Don't let heavy soil stop your project; we have the technical expertise to find a workaround.

When space is at a premium, we look at green roofs, permeable paving, or underground attenuation tanks. Our SuDS assessments focus on practical, cost-effective designs that fit your site’s footprint.

These are underground structures that hold excess water during storms. We calculate the exact size you need so you don't overspend on hardware while still meeting discharge limits.