What does radon mean when you are buying a house?

What are the Action Level and the Target Level?

Radon is a radioactive gas from the ground. You cannot see or smell it. UKHSA, through UKradon, recommends that radon is reduced in homes where the average is more than 200 becquerels per cubic metre (200 Bq/m3). That is the Action Level. It is an annual average, which is why a proper measurement is not a one-hour gadget reading. The Target Level is 100 Bq/m3. UKradon describes it as the ideal outcome for reduction work in existing buildings and for protection in new ones. If a result sits between the Target Level and the Action Level, UKradon says action to reduce the level should be considered, especially where someone in the home smokes or used to smoke.

Is the radon map a test of this house?

No. UKradon’s UK maps show where a higher level is more likely. The darker the colour, the greater the chance. That is as far as colour goes on this page: darker means a greater chance. The map does not tell you the level in a named house. Every building contains some radon, usually a low level. The only way to know whether a home is above or below the Action Level is to measure it.

Basements and cellars are the exception you do not read off the colour. UKradon says the map should not be used for basements, cellars or underground sites. Treat all of them as having a higher chance of high radon, regardless of where the map puts the street. A cellar used as a bedroom is a reason to measure, not a reason to argue with the shading.

What does the address search fee pay for?

UKradon’s radon searches page publishes an individual address search for homes and small workplaces, using the detailed dataset, for a fee of £3.90. That figure was reviewed on 24 October 2026. The search estimates the chance that the address is above the Action Level. It does not measure the radon in the building, and it is not a quote to reduce radon. This guide does not give a remediation cost. Anyone who offers you one without a measurement and a look at the floors is guessing.

The measurement UKradon describes uses two detectors, one in a bedroom and one in a living room, left for three months. Short tests swing around and are easier to misread. Solicitors in England and Wales often raise radon in the local-authority search. The address report can answer that style of question about whether the property is in an affected area. It still does not replace the three-month test if you need the level.

What can a survey say, and where do building regulations fit?

A home surveyor does not carry radon detectors as part of a normal inspection, and they cannot see the gas. They can note a basement, a sump, or a ventilated subfloor if those are visible, and they can tell you the map is not a reading. Ask them what they actually saw. Ask the seller whether a three-month test exists and, if it does, for a copy. A test from years ago, or from before the house was altered, is history rather than today’s average.

• Do not treat map colour as the result for this house. Darker means a greater chance, nothing more precise than that on this page.
• Treat basements and cellars as a higher chance even where the map looks light.
• Order a measurement with two detectors over three months if you need the level.
• The £3.90 address search is the published search fee, reviewed 24 October 2026. It is not a works quote.
• For new building work in England, radon protection is signposted in Approved Document C. That document is not a test of an existing home, and it is England guidance. Wales has its own building regulations.

Common questions