Flood
Blog
Understanding Product 4 Data: What It Is and Why It Matters
What is Product 4 data?
Product 4 datasets are designed to inform Flood Risk Assessments, which are required under planning regulations where Flood Risk Standing Advice applies. Product 4 is the most detailed modelled flood data held by the Environment Agency.
Each Product 4 dataset is requested on a site-by-site basis from the Environment Agency under the Freedom of Information Act 2000 and the Environmental Information Regulations 2004. Under EIR 2004, the Environment Agency has up to twenty working days to respond to a request, which can represent a significant delay for clients working under planning timescales.
Product 4 Environment Agency data
Clients often ask us about Product 4 (P4) data, because it can be the reason a Flood Risk Assessment is delayed. The report can be almost ready to go, only to be held up waiting for a data set that the client has had little visibility of and may not fully understand.
Clients have not had visibility of the data set or the request process, so the reasons behind the delay can be unclear. This blog explains what Product 4 data is, why FPS Environmental considers it essential to a robust Flood Risk Assessment, and where its limitations lie.
A standard Product 4 dataset contains modelled flood extents, depths, velocities and hazard ratings across a range of probability scenarios. The climate change layers are particularly important, as they are what allow a Flood Risk Assessment to demonstrate that a development will be safe over its lifetime, not just under current conditions. Output formats vary depending on when and how the underlying model was run.
The Environment Agency commissions hydraulic modelling on a catchment-by-catchment basis, with each model scoped, built and calibrated to reflect local flood mechanisms. The result is genuine variation in data quality and availability across different parts of the country.
At FPS Environmental, we use Product 4 data not only for site-specific Flood Risk Assessments where they are a planning requirement, but also for our Flood Mitigation Reports and Homebuyer Flood Risk Reports, where understanding climate-adjusted flood depths is essential to credible advice.
Why Product 4 data matters for a Flood Risk Assessment
A Flood Risk Assessment must demonstrate that a development will be safe for its lifetime. Under the National Planning Policy Framework, that lifetime is taken as 100 years or more for residential development. The standard requirement, set out in the Environment Agency’s Standing Advice, is the 1% Annual Exceedance Probability (AEP) flood event with climate change allowance applied.
Central climate change allowances for residential development typically range from +35% to +42%, depending on the river basin and the design epoch (commonly 2070 to 2115). The 1% AEP plus climate change scenario represents a reasonable worst-case event over the development’s lifespan, balancing safety with practicality.
The Product 4 dataset provides modelled flood levels for each return period and scenario, expressed in metres above Ordnance Datum (m AOD). Combined with LiDAR-derived ground levels, these allow us to calculate anticipated flood depths at the property.
A freeboard allowance is then added to set the recommended Finished Floor Level. Freeboard is an additional safety margin above the modelled flood level, providing protection against the inherent uncertainty in hydraulic modelling. The Environment Agency requires a minimum 300mm freeboard, with 600mm often expected in higher-risk areas. The calculation is therefore:
Finished Floor Level = Modelled 1% AEP + CC Flood Level + Freeboard
The 20-working-day response period for Product 4 can cause significant delays to client decisions, but the data is essential. It provides the technical foundation for accurate advice on a property’s risk profile both today and into the future, and it informs every stage of mitigation strategy. Understanding future flood depths and probabilities at a property can substantially change the recommendations of a report. For a homeowner, that often means the difference between proceeding with a purchase or stepping back. For a developer, it determines whether a scheme is viable as proposed, or whether finished floor levels, layout or mitigation strategy need to be revisited.
Limitations and challenges of Product 4 data
The most significant drawback of Product 4 data is the waiting time, but that is not the only challenge. The data supplied can be incomplete, low-resolution or outdated. In some areas, the Environment Agency holds no relevant modelled data at all.
From a flood consultant‘s perspective, Product 4 datasets can also be inconsistent in the way the data is presented and what is contained within them. This may lead to further delays for the client, as we sometimes need to return to the Environment Agency to request alternative datasets.
The shift to Product 6 raw data
In recent years, the Environment Agency has increasingly supplied raw model outputs (Product 6) rather than the more refined Product 4 datasets. Working with Product 6 requires significantly more resource and skill:
- Files are often over 10 GB and must be processed in GIS software for manual data extraction
- Download and processing typically takes half a working day or more
- Outputs require reformatting before they can be presented clearly to a client
This adds time and complexity to our work, but it also means we are working directly with the most granular hydraulic outputs the Environment Agency holds.
Final thoughts: is Product 4 data worth the wait?
Product 4 data is the technical foundation of credible flood risk advice. It is what allows a Flood Risk Assessment to do its actual job: assessing whether a site can be safely developed, not just whether it sits within a particular flood zone.
The wait is real, and the limitations are genuine. But for a process that determines whether a home can be built, sold, mortgaged or insured for the next century, Product 4 data is the difference between an assessment and a guess.
Written by Reece Hewitt, Flood Risk Consultant, 4th November 2025.
Further reading
At FPS Environmental, we investigate how sites behave. Flooding, drainage performance, levels and constraints. That insight feeds directly into our work, whether for planning, design or resolving existing issues.
This includes Flood Risk Assessments informed by Product 4 data, with featured locations across the country including Cumbria and Reading and the Thames Valley, alongside Bristol, Cornwall and Surrey.
