Radon is a natural radioactive gas that comes out of the ground and can build up inside homes. The UK radon map shows the chance that homes in an area have high levels, but it can’t tell you the level in a particular house. Only a three-month radon test can do that. Even in the highest-risk areas most homes are below the Action Level, and where they aren’t, the fix is usually straightforward.
Here’s how to check the map, what the searches mean when you’re buying, and what to do if a property is in a radon Affected Area.
What is radon gas?
Radon is a colourless, odourless gas produced by the natural decay of uranium found in small amounts in all rocks and soils. Outdoors it disperses harmlessly. Indoors it can collect, because a house is slightly warmer and at a slightly lower air pressure than the ground beneath it, which draws soil gas in through cracks in floors, gaps around pipes and suspended timber floors.
Long-term exposure to high radon levels increases the risk of lung cancer. Radon is widely recognised as the second biggest cause of lung cancer in the UK after smoking, and the risk is much greater for smokers and ex-smokers. It doesn’t cause any short-term symptoms, so you can’t tell whether a house has a problem without measuring it.
How do you read the UK radon map?
The radon maps are produced by the UK Health Security Agency (UKHSA) with the British Geological Survey (BGS), based on long-term radon measurements in hundreds of thousands of homes combined with geological mapping. The current map for Great Britain was updated in December 2022. You can view it free on UKradon.
- The map is shaded by the percentage of homes estimated to be at or above the Action Level in each area.
- White areas: less than 1 in 100 homes.
- Darkest areas: more than 1 in 3 homes.
- Anywhere with a 1% chance or more is called a radon Affected Area.
The free map is shown in 1km squares, so it’s indicative only. For a specific property, UKradon offers a paid address search, which gives the radon potential for that address. Your conveyancer’s searches usually include the same information.
Radon in Derbyshire and the North
Among the highest-risk areas on the map is the Derbyshire Peak District, alongside places such as Cornwall. Derbyshire Dales District Council confirms its area is a radon Affected Area. If you’re buying in or around the Peak District, checking radon is a sensible part of your due diligence.
The picture elsewhere in Yorkshire and the North varies over short distances with the underlying geology, so check the specific postcode rather than relying on what you’ve heard about the county or the town.
What are the radon Action Level and Target Level?
Radon is measured in becquerels per cubic metre (Bq/m³), averaged over a year. UK advice sets two figures for homes:
| Level | Annual average | What it means |
|---|---|---|
| Action Level | 200 Bq/m³ | At or above this, you should reduce radon levels |
| Target Level | 100 Bq/m³ | The ideal outcome of remedial work, and a level to consider acting at if anyone in the home smokes |
Between 100 and 200 Bq/m³ is a grey area. Government advice is that householders in that range should seriously consider reducing levels, particularly where occupants smoke or used to.
How does a radon test work?
The standard home test uses two small passive detectors:
- One goes in the main living area and one in an occupied bedroom.
- They stay in place for three months, which smooths out the large day-to-day and seasonal variations in radon.
- You post them back to the laboratory, and the result arrives a few weeks later as an annual average compared against the Action Level.
UKradon sells home measurement packs, and other validated laboratories offer the same service. Short “instant” readings from a cheap electronic monitor can be interesting, but they aren’t a substitute for a three-month test when making decisions.
What does the CON29 search say about radon?
When you buy a house in England or Wales, your conveyancer orders a local authority search. The standard enquiries on the CON29 form include a question asking whether the property is in a radon Affected Area. Environmental search reports usually cover it too.
A “yes” answer doesn’t mean the house has a radon problem. It means the chance of high radon in that area is at least 1%. The seller’s TA6 Property Information Form also includes questions about radon, so check the seller’s answers when your solicitor sends them through.
What should a buyer do if the property is in a radon Affected Area?
UKradon’s guidance for house sales suggests:
- Ask the seller for a test result. A valid three-month test, ideally in the current layout of the house, answers the question.
- Ask whether any radon protection or remedial system is fitted, such as a sump and fan, and whether it has been retested since.
- If there’s no test, ask your solicitor about a retention: a sum held back from the purchase price for a set period while you move in and carry out a three-month test. If the result is below the Action Level, the money goes to the seller. If it’s above, it pays for the remedial work. UKradon’s house-sale guidance gives a typical retention range of £800 to £3,000.
- Test in the first year of living there, even if you didn’t arrange a retention.
Because a test takes three months, radon very rarely needs to hold up a purchase. It’s a known, manageable risk to plan for rather than a reason to walk away.
How is high radon reduced?
Radon remediation is usually simpler and cheaper than people expect. The main approaches are:
- Radon sump. A small cavity is dug beneath the ground floor slab, connected by a pipe to a small electric fan that draws soil gas out and vents it safely outside. Government research has found an active sump is the most effective method, reducing levels on average around six-fold.
- Positive ventilation. A fan unit, often in the loft, gently pushes fresh air into the house. It works best in well-insulated, draught-free homes, and is generally suited to moderately raised levels rather than very high ones.
- Improving underfloor ventilation in houses with suspended timber floors, for example by adding or clearing air bricks or fitting a fan.
- Sealing floors and gaps, which helps on its own only modestly but supports other measures.
After any work, retest to confirm the level has come down. A remedial system with a fan needs power and an occasional check, like any other mechanical system.
Radon and new-build homes
Under the Building Regulations, new homes and extensions in radon Affected Areas need radon protective measures. In England and Wales, guidance linked to Approved Document C sets out “basic” protection (a gas-tight radon barrier across the ground floor) in moderately affected areas and “full” protection (the barrier plus a capped standby sump or a ventilated sub-floor) where the risk is higher. Protection reduces the risk, but it isn’t a guarantee, and a test is still worthwhile once you’ve moved in.
Does a house survey check for radon?
A surveyor can’t measure radon during a normal inspection. What a Home Survey Level 2 or Level 3 can do is flag where the property sits in a known radon area, note any visible remedial system such as a sump pipe and fan, and point you and your solicitor to the right questions. Our guide to what a surveyor looks for explains where radon fits alongside flooding, trees and other risks, and questions to ask before you offer covers what to raise with the agent early. When you view, our house viewing checklist is a good prompt to look for a radon fan or sump pipe.
If you’re buying in Yorkshire, the Peak District or the surrounding area, get in touch for a fixed-fee quote for the property, or use our survey cost calculator.
Sources and further reading
- UKradon — UK Health Security Agency
- Radon and house sales — UKradon (UKHSA)
- Radon Action Level and Target Level — UKradon (UKHSA)
- Updated radon map for Great Britain published — British Geological Survey
- Radon — Derbyshire Dales District Council