Flood risk — methodology

1. Data sources, licence and freshness

The flood section is built from five Environment Agency datasets. The first four are loaded into our PostGIS database via ETL and refreshed periodically; the fifth is queried live every time a report is generated.

• Flood zones (rivers and the sea) — EA Flood Map for Planning, zones 1, 2, 3a and 3b. Loaded into our flood_zones table.
• Surface water flood risk — EA NaFRA2 Risk of Flooding from Surface Water (RoFSW), four bands: high (>3.3% annual chance), medium (1-3.3%), low (0.1-1%), very low (<0.1%). The published polygons already include the UKCP18 RCP8.5 mid-century climate uplift. Loaded into our rofsw_zones table. © Environment Agency copyright and/or database right 2025.
• Recorded historical flood outlines — EA dataset of mapped flood events, including event date and source where recorded. Loaded into our historical_flood_outlines table.
• Flood defences — EA spatial dataset of constructed flood defences, queried within a 500m radius of the postcode centroid. Loaded into our flood_defences table.
• Live flood warnings and alerts — Environment Agency Flood Monitoring API, queried in real time at report generation, with a 5km search radius.

Licence: all five datasets are published by the Environment Agency under the Open Government Licence v3.0. Contains Environment Agency information © Environment Agency and database right.

Freshness: our ETL refreshes the four spatial datasets on a rolling schedule. Live flood warnings are fetched at the moment your report is generated, so they reflect the warning state published by the Environment Agency at that time. The EA itself updates flood zones and surface water bands periodically — typically once per year, with full re-mapping cycles spanning several years — so the underlying model your report quotes may be a year or more old.

2. What we do

• Resolve the property's postcode to a centroid using Postcodes.io (ONS-derived).
• Look up the Environment Agency flood zone (1, 2, 3a or 3b) at that point.
• Read the EA surface water band (high / medium / low / none) at that point.
• Return any recorded historical flood outlines that intersect the postcode.
• List the nearest flood defences within 500m, with the count and proximity.
• Pull any live flood warnings or alerts within 5km at report time.
• Combine the above into an overall risk band (very low / low / medium / high / very high) using a transparent rule: the higher of the river/sea zone risk and the surface water risk, bumped up one band when there are recorded historical events.
• Where Flood Zone 3a or 3b applies, surface a planning note that any new development requires a Flood Risk Assessment and the Sequential Test, per national policy.

3. What we don't do

• We do not commission or perform a Flood Risk Assessment. A formal FRA models the specific site, finished floor levels, drainage, defences and climate allowances — that requires a chartered surveyor or specialist consultant.
• We do not assess insurance or insurability. We make no statement about premiums, Flood Re eligibility, insurer appetite, or the cost or availability of cover. Home-Checker is not authorised or regulated by the Financial Conduct Authority and provides no insurance advice.
• We do not estimate flood damage cost or property value impact.
• We do not check internal property factors. Sub-floor voids, air bricks, drain conditions, sewer capacity, sump pumps, and resilience measures are outside our scope and require a physical survey.
• We do not model groundwater or reservoir flood risk in detail. Those EA datasets exist but are not currently part of this section.

4. Known limitations

We want you to understand exactly where our flood section is strong and where it is weak before you rely on it.

• Resolution. We query the postcode centroid, not the building footprint. UK postcodes typically cover 10–80 properties; in rural areas a single postcode can span hundreds of metres. Flood risk can vary materially across that distance, especially near rivers, on steep ground, or where surface water collects. For Zone 2/3 properties, always check the Environment Agency's address-level Check Long-Term Flood Risk service.
• Modelling vintage. EA flood zones are model-based and updated on multi-year cycles. Recent drainage improvements, defence schemes, planning consents or watercourse works may not be reflected.
• Surface water classification gaps. Where the RoFSW dataset has not yet been loaded, or where the model produces no classification for a point, we return an explicit "data pending" state and surface it as a data gap rather than silently falling back to "very low". Treat any unflagged green band as the absence of an answer, not an all-clear.
• Historical floods are recorded events only. Many real-world flood events were never reported to or mapped by the EA. An empty historical-flood result does not prove the property has never flooded.
• Defences reduce but do not eliminate risk. A property "behind" defences is still in the underlying flood zone; defences are designed to a stated standard (commonly 1 in 100 years) and can be overtopped or breached. We list defences within 500m as context, not as a guarantee of protection.
• Climate change is not separately modelled. EA flood zones include a climate-change allowance, but we do not run our own future-scenario projections.
• England only. Our flood section covers England. Scottish (SEPA), Welsh (NRW) and Northern Irish equivalents are not included.

5. What this is not a substitute for

6. Further reading

• Methodology overview — how the whole report is built.
• Report disclaimer — limits of liability and the scope of all sections.
• Data sources & attribution — full licence detail for every source we use.
• Environment Agency — Check Long-Term Flood Risk (the canonical address-level service for England).