What Radon Is and Why It Matters
Radon is measured in becquerels per cubic metre (Bq/m³). The UK Action Level — set by the UK Health Security Agency (UKHSA) — is 200 Bq/m³. Properties above this level should have remediation measures installed. The Target Level (the level you should aim for through remediation) is 100 Bq/m³. The average UK home has a radon level of around 20 Bq/m³.
The health risk is cumulative — it depends on the level of radon and the length of time spent in the building. Living in a home at 200 Bq/m³ for 30 years carries a meaningful additional cancer risk. Smokers in high-radon homes face a substantially elevated risk — the two risk factors interact multiplicatively, not additively.
Radon enters properties through gaps in floors, cracks in walls below ground level, gaps around service pipes, and through porous construction materials. Ground-floor rooms and basements typically have higher concentrations than upper floors. An older property with a solid concrete floor and no damp-proof membrane may be more susceptible than a modern property with a sealed slab.
High-Radon Areas in the UK
Radon levels in the UK are strongly linked to geology — specifically the presence of granite, limestone, and certain sedimentary rocks that contain higher concentrations of uranium. The UKHSA publishes free postcode-level radon potential maps that show the probability of a property in that postcode exceeding the Action Level.
The highest-risk areas are concentrated in a relatively small number of regions. Buyers in these areas should commission a radon assessment as a matter of course.
| Region | High-risk areas | Typical concern level |
|---|---|---|
| Devon | Dartmoor, South Hams, parts of Exeter district | Very high — among UK's highest concentrations |
| Cornwall | Most of the county, particularly the granite moors | Very high — granite geology throughout |
| Derbyshire | Peak District, parts of Derbyshire Dales | High — limestone geology |
| Northamptonshire | Parts of the county on ironstone and limestone | Moderate to high |
| Somerset | Mendip Hills area | Moderate to high — limestone karst |
| Lincolnshire | Parts of the Wolds (limestone) | Moderate |
| Yorkshire | Parts of the Dales (limestone) and North York Moors | Moderate |
| Derbyshire/Nottinghamshire | Former coalfield areas (some sandstone) | Patchy — check postcode |
How to Check a Property's Radon Risk
The UKHSA's Radon Map is available at ukhsa.gov.uk and shows the percentage of homes in any postcode that are estimated to exceed the Action Level. A postcode where more than 3% of homes exceed the Action Level is designated as a 'radon Affected Area' — this is the threshold where the UKHSA recommends that new occupants test their home.
A postcode-level estimate tells you the risk probability — it does not tell you the actual radon level in a specific property. The only way to know the true level is to carry out a radon measurement. The standard method uses small plastic detector devices (alphaTRACK or electret ion chamber) placed in main living areas and bedrooms for a minimum of three months — ideally over winter, when homes are less ventilated and levels are highest.
Radon detectors can be ordered directly from the UKHSA, the British Geological Survey, or specialist suppliers for around £50–£80 for two detectors. When purchasing a property in a high-risk area, you can ask the seller to provide existing radon measurement results — though many sellers will not have tested. Your environmental search (a standard disbursement in conveyancing) will include a radon risk indicator for the postcode.
Radon Mitigation
Properties above the Action Level can almost always be brought below the Target Level through straightforward remediation. The most common and cost-effective method is a radon sump — a small pit dug under the ground floor with a low-power fan that draws radon from beneath the floor and vents it harmlessly outside. Installation typically costs £800–£1,500 and can reduce radon levels by 80–90% in most properties.
Other mitigation methods include positive pressure ventilation (blowing air into the property from outside, diluting the radon), sealing floors and walls to prevent ingress, and improving natural ventilation. The appropriate method depends on the property's construction. In new builds in high-risk areas, Building Regulations require radon-resistant construction measures to be installed as standard.
Once remediation is installed, a follow-up measurement after 3–6 months confirms effectiveness. Most properly installed sumps reduce levels well below the Target Level. The ongoing running cost is minimal — a standard radon sump fan uses about the same electricity as a low-energy light bulb.
Effect on Insurance and Mortgages
Standard buildings and contents insurance policies do not typically exclude or load premiums for radon risk — it is not a risk that insurers currently price into mainstream residential policies. Similarly, standard mortgage lenders do not assess radon as a lending risk in the way they assess flood risk or structural defects.
The practical implication is that buying a property in a high-radon area, or even a property with known high radon levels, does not by itself create mortgage or insurance difficulties. The risk is a health risk, not a financial one for lenders or insurers. However, if you are selling a property that has had a radon test, you should disclose the results in the TA6 Property Information Form to avoid potential misrepresentation claims.
Key Takeaways
- ✓Radon is the UK's second leading cause of lung cancer — properties in affected areas should be tested
- ✓High-risk areas include Devon, Cornwall, Derbyshire Peak District, Northamptonshire, and parts of Somerset
- ✓Check postcode-level risk for free on the UKHSA Radon Map — your environmental search will include a radon indicator
- ✓If levels exceed 200 Bq/m³ (the Action Level), remediation via a radon sump costs £800–£1,500 and reduces levels by 80–90%
- ✓Radon does not currently affect mortgage eligibility or standard insurance premiums