Most of the searches in a bundle deal with things you can point at. A road. A planning notice. A mine entry. Radon is the one that deals with something you can't see, smell or measure from a map alone.
It's a gas. It comes out of the ground, and in the wrong house it builds up indoors.
A radon report won't tell you the level in a particular home. What it will tell you is whether the address sits somewhere the level is worth checking. For a property in the wrong part of the country, that matters. Here's what a radon report shows, what a Radon Affected Area actually means, and where it fits in the search bundle.
What is radon and why does it matter?
Radon is a naturally occurring radioactive gas, produced by the decay of uranium in rock and soil. Outdoors it disperses harmlessly. Indoors it can accumulate to levels that matter, and prolonged exposure is a recognised cause of lung cancer, the second-largest cause after smoking.
You cannot detect radon with your senses. It has no colour, no smell and no taste, which is exactly why it goes unnoticed in homes that have it. The gas seeps up through floors, gaps and service entries, then concentrates in enclosed ground-floor spaces.
How much builds up depends on two things: the geology under the property, and how the building sits on it. The same ground can produce a high reading in one house and a low one next door, depending on construction and ventilation. That's why a report estimates risk and a test confirms the actual level.
What does a radon report show?
A radon report estimates the probability that a property exceeds the UK home Action Level of 200 Bq/m3, shown as a probability band rather than a single number. It is a risk estimate based on geology and location, mapped by UKradon (UKHSA/BGS). It does not measure the gas inside the building.
The band is the part conveyancers read first. A low band means the chance of the home exceeding the Action Level is small. A higher band means a meaningful chance, and a clear prompt to test. The report turns "this area has radon" into "this address has roughly this likelihood of a problem".
What a radon report does not do is replace a test. The only way to know the actual level in a specific home is to place detectors and measure over a period of months. The report tells you whether that's worth doing. For an address in a low band, usually not. For one in a high band, yes.
| Probability of exceeding the Action Level | What it indicates |
|---|---|
| Below 1% | Not in a Radon Affected Area; testing not normally indicated |
| 1% or greater | In a Radon Affected Area; a radon test is advised |
| Higher bands within an affected area | Greater likelihood of a high reading; testing is more strongly advised |
What is a Radon Affected Area?
A Radon Affected Area is an area where there is a 1% or greater chance that a home is at or above the Action Level of 200 Bq/m3. That threshold, a 1% probability, is the line that defines whether an address counts as affected. The areas are mapped for Great Britain by UKHSA and the British Geological Survey.
The mapping is precise, not a vague band across a region. Two homes on the same street can fall on different sides of the line, because the geology underneath them differs. The GOV.UK radon map reflects this, working at a fine resolution rather than painting whole counties as risky.
That precision is why "this property is in Devon" tells you nothing useful on its own. Radon risk concentrates where the geology drives it: parts of Cornwall, parts of Devon, parts of Somerset, parts of Derbyshire and parts of Northamptonshire, among others. Plenty of addresses inside those counties carry no meaningful radon risk at all. The map decides, address by address, not the county name.
How does radon reach the search bundle?
Radon risk reaches the conveyancer through the environmental search rather than as a standalone product in most bundles. The environmental search flags whether the property sits in a Radon Affected Area. If it does, that flag is the trigger for the next step: advise the buyer to test, and to mitigate if the test comes back high.
So for the search firm, radon usually isn't a separate order to remember. It rides inside the environmental data. The operational job is making sure the environmental search is on the bundle in the first place, and that the radon flag inside it isn't lost in a long report nobody reads to the end.
The follow-through is the conveyancer's. Where an affected address is flagged, the buyer can arrange a radon test, and if the level is high, mitigation is well established: improved underfloor ventilation, a radon sump, sealing entry points. None of that needs to derail a transaction. It needs to be known about before completion, not after.
"Radon never caused me the grief the council searches did, because it's mostly carried in the environmental data. The mistake I saw was treating the affected-area flag as background noise. It isn't. For the buyer of that one house, it's the line in the report that actually changes what they should do next."
— Valerie Bennett, Personal Search Veteran · June 2026
Does an affected-area result stop a sale?
No. A Radon Affected Area result is a prompt to test, not a defect that blocks a transaction. Most affected addresses, once tested, sit below the Action Level. Where a test does come back high, mitigation is routine and effective, and the work is modest compared with the structural issues other searches turn up.
The thing to avoid is treating the flag as either trivial or alarming. It's neither. It's information that points to a sensible, proportionate next step: measure the actual level, then act only if the measurement warrants it.
Handled that way, radon is one of the more manageable risks in a bundle. The geology is mapped, the threshold is defined, the test is cheap relative to the house, and the fix works. The only real failure is the flag being there and nobody acting on it.
Key takeaways
Radon is a naturally occurring radioactive gas from uranium decay in the ground, and a recognised lung-cancer risk indoors. A radon report estimates the probability a property exceeds the UK home Action Level of 200 Bq/m3, shown as a probability band, using mapping from UKHSA and the British Geological Survey.
A property is in a Radon Affected Area when there's a 1% or greater chance of a home at or above the Action Level. Those areas concentrate where geology drives them, in parts of Cornwall, Devon, Somerset, Derbyshire and Northamptonshire among others, not across whole counties.
For the search firm, radon comes through the environmental search. The job is making sure that search is on the bundle and the affected-area flag is acted on: test, then mitigate if the result is high.
Conveyancing searches explained → · What a local authority search shows → · How council data works in Valio →