Radon map: check radon gas levels by postcode
Radon is a natural radioactive gas that seeps from the ground and can build up indoors. It is the largest source of radiation exposure for most people in the UK, and long-term exposure at high levels raises lung cancer risk. How much radon an area produces depends on its geology, so the potential varies street by street. Enter a postcode to see the radon potential class for its 1 km grid square.
What the classes mean
The British Geological Survey and the UK Health Security Agency class each 1 km square of Great Britain by the estimated share of homes at or above the radon action level of 200 becquerels per cubic metre. Any area at class 2 or above counts as a radon Affected Area. Across England and Wales, 47.7% of postcodes sit in an Affected Area on this basis.
| Class | Homes at or above the action level | Postcodes (E&W) |
|---|---|---|
| 1 (lowest) | fewer than 1 in 100 homes | 830,093 |
| 2 | 1 to 3 homes in 100 | 307,670 |
| 3 | 3 to 5 homes in 100 | 147,027 |
| 4 | 5 to 10 homes in 100 | 137,174 |
| 5 | 10 to 30 homes in 100 | 115,473 |
| 6 (highest) | more than 30 homes in 100 | 48,964 |
Highest-radon local authorities
Ranked by the share of postcodes in class 5 or 6, where at least 1 home in 10 is estimated to be at or above the action level. The granite and limestone areas of the South West, the Pennines and mid Wales dominate.
| # | Local authority | Postcodes in class 5-6 | In an Affected Area (class 2+) |
|---|---|---|---|
| 1 | West Devon | 93% | 99.9% |
| 2 | Isles of Scilly | 92.6% | 100% |
| 3 | South Hams | 90.4% | 100% |
| 4 | Cornwall | 89.6% | 99.7% |
| 5 | Flintshire | 83.9% | 94.5% |
| 6 | Bath and North East Somerset | 82.8% | 99.4% |
| 7 | Lewes | 72.7% | 85.8% |
| 8 | Derbyshire Dales | 72% | 87.4% |
| 9 | North Northamptonshire | 69% | 96% |
| 10 | Pembrokeshire | 67.9% | 99.8% |
| 11 | Dover | 65.7% | 83.2% |
| 12 | Stroud | 62.6% | 87.1% |
| 13 | Bridgend | 62.2% | 94.1% |
| 14 | Rutland | 60.7% | 99.7% |
| 15 | Wrexham | 57.9% | 94.8% |
What to do about a high reading
A high potential class says testing is worth doing; the only way to know a home’s actual level is a 3-month detector test, which costs around £50 through UKradon, the official UKHSA service. Where measured levels are high, fixes range from improved under-floor ventilation to a radon sump with a fan, typically costing a few hundred to a couple of thousand pounds. Radon also features in property searches: solicitors routinely flag Affected Areas during conveyancing.