Radon is one of those property risks that most homeowners have never heard of, until it is discovered during a survey or environmental search. It’s a naturally occurring radioactive gas that seeps into buildings from the ground, and in certain parts of the UK, it’s common enough to affect property transactions.
It’s not something to panic about. But if you’re buying, selling, or living in an affected area, it’s worth understanding what it is, how to test for it, and what your options are.
What radon actually is
Radon is a naturally occurring radioactive gas. It’s produced by the decay of uranium in rocks and soil, particularly granite, limestone, and certain shales. It seeps up through the ground and into buildings, where it can accumulate to dangerous concentrations, especially on ground floors and in poorly ventilated spaces.
You can’t see it, smell it, or taste it. The only way to know if it’s in your home is to test for it.
Where in the UK is most affected
Radon risk is driven by geology. Some areas have significantly higher concentrations than others.
The highest-risk regions include:
- Cornwall is the most affected county in England. In parts of Cornwall, more than 1 in 5 homes exceed the action level.
- Devon, particularly Dartmoor and the surrounding areas
- Somerset, especially the Mendip Hills
- Derbyshire, the Peak District and limestone areas
- Northamptonshire has elevated risk areas across the county
- Parts of Wales, Lancashire, and the Scottish Borders
- Aberdeenshire and parts of the Scottish Highlands
London and the South East generally have very low levels.
A “Radon Affected Area” is any area where 1% or more of homes are estimated to exceed the UK action level. Approximately 5% of UK homes fall into this category, that’s hundreds of thousands of properties.
Why it matters for your health
Radon is the second largest cause of lung cancer in the UK after smoking. When radon gas is inhaled, its radioactive decay products become trapped in lung tissue, where they emit radiation that can damage DNA over time.The numbers:
- Around 1,100 lung cancer deaths per year in the UK are linked to radon
- Radon accounts for approximately 5% of all UK lung cancers
- For non-smokers, the risk at the UK action level (200 Bq/m³) is relatively small around 0.5% cumulative lifetime risk
- For smokers, the same radon level pushes the risk to approximately 19% the effects are synergistic, not additive
There is no safe threshold. Around 90% of radon-induced lung cancers occur in homes below the action level, simply because that’s where most people live.
The UK action level: 200 bq/m³
The UK action level is 200 becquerels per cubic metre. At or above this level, the UK Health Security Agency recommends taking action to reduce radon.
There’s also a target level of 100 Bq/m³, the recommended maximum even where levels are below the formal action level.
For context, the World Health Organisation recommends a reference level of 300 Bq/m³. The UK standard is stricter.
For new buildings in Radon Affected Areas, Building Regulations (Approved Document C) already require radon protective measures to be installed during construction.
How to test your home
Testing is straightforward and inexpensive.
You order a pack containing two small detectors, roughly matchbox-sized passive devices. One goes in the main bedroom, one in the living room. They sit there for three months, collecting data. You then post them back to a laboratory for analysis.
The cost: around £50–£55 for the official UKHSA measurement pack via ukradon.org, including both detectors and lab analysis.
Shorter 10-day screening tests exist and are sometimes used in property transactions, but they’re less reliable. The three-month test is the standard recommended by UKHSA.
That’s it. Under £55, a few minutes to set up, and three months later you have a definitive answer.
What to do if levels are high
If your test comes back above 200 Bq/m³, there are several proven solutions. The right one depends on your property’s floor type and the severity of the reading.
Active radon sump, the most effective and widely recommended solution. A fan-driven pipe draws radon from beneath the floor slab and vents it safely outside. Typical cost: £1,400–£3,000 installed professionally.
Positive input ventilation (PIV), a fan unit, usually installed in the loft, pushes fresh air into the building and dilutes radon concentrations. Typical cost: £550–£1,000.Improved underfloor ventilation, for properties with suspended timber floors, adding or improving air bricks to increase cross-ventilation can be enough. Typical cost: £200–£600.
Radon-proof membrane, installed during construction or major renovation as a physical barrier. Cost varies as part of a broader build project.
Most solutions reduce radon levels by 90% or more. The investment is modest relative to what the property is worth and relative to the health risk of doing nothing.
Radon and selling your home
This is where it gets practical for homeowners and buyers.
The TA6 Property Information Form which sellers complete as part of every residential sale in England and Wales asks specific questions about radon:
- Question 7.4: Has radon testing been carried out? If yes, provide the report and confirm whether results are below the action level.
- Question 7.5: Were radon protective measures installed during construction?
Providing false or incomplete answers is a legal misrepresentation. And even if you haven’t tested, the buyer’s solicitor will likely order an environmental search that flags whether the property is in a Radon Affected Area.
If the search comes back positive and you have no test results to provide, the buyer may request testing as a condition of proceeding, adding weeks or months to the transaction. If levels are elevated and no mitigation is in place, the buyer may renegotiate or walk away.
The pragmatic move for sellers in affected areas: test before you list. A clean result costs £55 and removes the issue entirely. An elevated result gives you time to install mitigation, typically a few days of work, and present the buyer with a resolved problem rather than an open question.
Does radon affect your mortgage?
It can.
Surveyors conducting mortgage valuations are expected to flag radon risk and reflect the need for mitigation in their assessment. In known Affected Areas, some lenders require radon testing before releasing funds.
Where high levels are confirmed, and no mitigation exists, lenders may downvalue the property or withhold funds until the issue is addressed. This doesn’t happen on every transaction, but it happens often enough that it’s worth being prepared for.
New builds in Radon Affected Areas must comply with Building Regulations on radon protection as a condition of sign-off, which in turn affects mortgage eligibility.
The bottom line: unmitigated radon in an Affected Area can delay or derail a mortgage offer. A £55 test and, if needed, a remediation costing a few thousand pounds is a small price to avoid that.
What most people get wrong about radon
“My neighbour tested and was fine, so I must be too.”
Radon levels can vary significantly between adjacent properties. Geology, construction type, ventilation, and even cracks in the floor slab all affect how much radon enters a specific building. Your neighbour’s result tells you nothing about your home.
“It’s only a problem in old houses.”
Radon affects new builds too, that’s why Building Regulations require protective measures in Affected Areas. A modern, well-sealed home can actually trap more radon than an older, draughtier one.
“We’re not in Cornwall, so we’re fine.”
Cornwall has the highest concentrations, but elevated radon is found across England, Wales, Scotland, and Northern Ireland. Parts of Derbyshire, Somerset, Northamptonshire, and the Scottish Highlands all have significant risk areas.
“If it was dangerous, someone would have told us.”
Nobody is required to tell you. There’s no mandatory testing programme for existing homes. Unless you test, you won’t know.
Check your property
If you’re not sure whether your home is in a Radon Affected Area, you can check for free on the UK radon map at ukradon.org.
If you’re buying, ask whether radon testing has been done and if it hasn’t, factor the cost and time of a three-month test into your planning.If you’re selling in an affected area, test before you market. It’s one of the cheapest things you can do to protect your sale.
And if you’re staying put, a £55 test is a small investment for knowing that the air in your home is safe.