Radon, underfoot.
Eavesdrop checks 66 sources public registers before you offer. For properties in affected postcode areas, the report includes the UKHSA radon potential classification and whether building regulations require protective measures — information that most estate agents will not volunteer.
What radon is and where it comes from
Radon is a naturally occurring radioactive gas formed by the decay of uranium in rocks and soil. It is colourless, odourless, and tasteless. It seeps upward through soil and rock, accumulating in enclosed spaces — particularly ground floors and basements. Long-term exposure is the second leading cause of lung cancer in the UK after tobacco smoke, accounting for around 1,100 deaths per year (citing UK Health Security Agency, Indoor Radon Map of England and Wales, updated 2024).
Radon levels vary significantly at a local scale — even between neighbouring houses — depending on ground conditions, foundation type, ventilation, and building construction. A property in a high-potential area may measure well below the action level, and a property in a low-potential area can occasionally test high. This is why measurement matters rather than postcode alone.
The Action Level and the Target Level
The UK Health Security Agency sets two thresholds for residential properties (citing UKHSA radon dose limits and Public Health England guidance, updated 2021):
Geographic affected areas
The British Geological Survey and UKHSA jointly publish the Radon Potential Map of Great Britain, which classifies areas by the percentage of homes estimated to exceed the Action Level (citing British Geological Survey Radon Potential Map, 2007, updated with UKHSA data 2021). Areas with 1% or more of homes estimated above the Action Level are designated "radon affected" for building regulation purposes.
The highest-potential regions in England include: Cornwall and parts of Devon (granitic geology of Dartmoor and Bodmin Moor), Derbyshire Peak District (limestone and gritstone), Northamptonshire (Northampton Sand ironstone), parts of Somerset, Shropshire, and Lincolnshire. In Scotland, Aberdeen and parts of the Highlands are the most affected due to granite bedrock (citing BGS Radon Potential Map).
Much of Greater London, the Midlands, and the North West fall into lower-potential categories, but this does not mean zero risk — it means the proportion of homes expected to exceed the Action Level is below 1%.
How to measure radon properly
The standard measurement method uses passive alpha track detectors placed in the living room and a bedroom for a minimum of three months (ideally over the winter, when levels are typically higher due to reduced ventilation). The detectors are then sent to a UKHSA-validated laboratory for analysis. Two detectors cost approximately £50–£70 including laboratory analysis (citing UKHSA Radon Measurement Validation Scheme).
Short-term electronic monitors are available but are not considered sufficient for property decisions due to the natural variability of radon levels. For a pre-purchase decision, a three-month test is the minimum standard. In practice, buyers in affected areas should either request vendor test results or commission their own test post-exchange conditional on acceptable levels.
Mitigation approaches
Where radon levels exceed the Action Level, several mitigation approaches are available. The most common, recommended in BRE Report BR 211 (Radon: Guidance on Protective Measures for New Buildings, BRE Press), are:
Building Regulations Part C — new builds
Approved Document C (Site Preparation and Resistance to Contaminants and Moisture, 2013 edition with 2013 amendments) requires radon protective measures in new-build properties located in areas where the radon potential exceeds 3% (citing Approved Document C 2013, §3.2). In areas with 10% or higher potential, full protective measures including sumps are mandatory.
For buyers of new-build properties in affected areas, confirmation that these measures were installed at construction and the relevant building regulations completion certificate was issued provides assurance. Eavesdrop checks whether the property postcode falls within an affected area as defined by UKHSA and BGS data, and flags this in the report.
What Eavesdrop checks
For every property report, Eavesdrop performs a UKHSA radon affected area lookup by postcode against the published radon potential dataset. The report states whether the property is in an area where building regulations require radon protective measures, the estimated percentage of homes in the area exceeding the Action Level, and links to the relevant UKHSA radon measurement guidance for buyers who wish to commission a professional test before exchange.