Radon under your postcode, mapped

Common questions

What is radon and why does it matter for a property?

Radon is a naturally occurring radioactive gas produced by the decay of uranium in rocks and soils. It seeps into buildings through foundations, floors and walls, and accumulates indoors. Prolonged exposure to elevated radon concentrations increases lung cancer risk — the UK Health Security Agency (UKHSA) estimates radon causes around 1,100 lung cancer deaths per year in the UK. Unlike flood or EPC risk, radon is invisible and odourless; it can only be detected by a home test. The UK action level is 200 becquerels per cubic metre (Bq/m³); above this level, remediation is recommended.

What do the BGS radon classes 1–6 mean?

The British Geological Survey (BGS) and UKHSA classify postcode areas into six radon potential bands based on the estimated percentage of homes above the UK action level (200 Bq/m³). Class 1 means fewer than 1% of homes in the area are above the action level — the lowest risk band. Class 6 means more than 30% of homes exceed the action level — the highest risk band. The classes are derived from a survey of 450,000 homes and are area-level estimates: two houses on the same street can have very different actual radon concentrations. A class 3 or above warrants a home test before purchase (UKHSA guidance, 2024).

What is the radon action level and what triggers it?

The UK action level is 200 Bq/m³ as an annual average, set by UKHSA and PHE. When a home test result exceeds this level, UKHSA recommends remediation — typically sub-slab or sub-floor ventilation (a radon sump), positive-pressure ventilation, or sealing entry points. The 2024 UKHSA 'Radon: guidance and information' report confirms this threshold has been in force since 1990 and is aligned with the WHO guideline of 100 Bq/m³. In practice, most homes in class 1–3 areas test below the action level; homes in class 5–6 areas should always be tested.

How do I test a property for radon before buying?

The most reliable method is a long-term alpha-track detector test lasting 90 days, placed in the main living areas and a bedroom. The UKHSA-approved provider is the UK Radon Association (www.radon.co.uk), and the Building Research Establishment (BRE) also offers certified testing kits. Short-term electronic monitors (such as RadonEye) give indicative readings but are not a substitute for the 90-day test. Testing kits cost £30–£60 and should be commissioned before exchange of contracts. If the measured level exceeds 200 Bq/m³, obtain a remediation quote — typical sump installation costs £600–£1,500 for a standard semi-detached property.

How much does radon mitigation cost?

Standard radon remediation in a UK residential property typically costs £600–£1,500 for a radon sump system (sub-slab depressurisation), fitted by a UKHSA-recognised contractor. Positive-pressure ventilation systems (also called positive input ventilation, PIV) are an alternative at similar cost. In severe cases — particularly in Class 5 or 6 areas or older stone properties — costs can rise to £2,500–£4,000 if significant structural sealing is needed alongside the sump. All costs should be factored into purchase negotiations if a test confirms levels above 200 Bq/m³. Eavesdrop's full report (£9.99) includes the BGS radon class checked against the property's UPRN postcode sector.