Radon is a natural, colourless and odourless radioactive gas that can build up inside buildings. The UK Health Security Agency (UKHSA) advises testing your home if you live or work in an Affected Area on its radon map. The action level is 200 becquerels per cubic metre (Bq/m3) as an annual average. The test uses two detectors left in your home for three months, and the UKHSA measurement service costs £52.80 including VAT at the time of writing.
What radon is and why it matters
Radon is a natural radioactive gas from rock and soil. It is colourless, odourless and tasteless, which means human senses cannot detect it. It can build up inside buildings.
Exposure to this gas has serious health implications over the long term. Northern Ireland government guidance describes exposure as the second-greatest cause of lung cancer, after smoking.
A news story published on 2 December 2022 by the UK Health Security Agency and the British Geological Survey attributed radon to about 1,100 lung cancer deaths per year in the UK. The risk is highest among smokers and ex-smokers.
UKHSA says that for most people the risk remains low, and the vast majority of buildings remain outside Affected Areas.
How to check the radon map for your address
The UK Health Security Agency and the British Geological Survey launched a new radon map for Great Britain on 1 December 2022, which was updated on 22 October 2025 to include the Isle of Man. The map shows where higher levels are more likely to occur.
The map uses a colour scale to show the chance of a higher level. You can search the map online for your area.
- White areas have a chance below one in a hundred.
- Darker colours mean a greater chance of a higher level.
- The darkest areas mean the chance is above one in three.
UKHSA advises people to test their home if they live or work in an Affected Area. The map is a broad guide and cannot tell you the level inside a specific building. Indoor radon often varies from building to building in the same area.
To get a more precise assessment for a single property, you can buy a radon address search report. This report gives the estimated probability of the property being above the action level. It is important to note that the map should not be used for basements, cellars or underground sites.
The action level explained
To help homeowners understand their test results, the government uses a specific threshold called the action level. The UK Health Security Agency recommends that radon levels should be reduced in homes where the average is more than 200 becquerels per cubic metre. The Government has endorsed this.
This level refers to the annual average, rather than a snapshot taken on a single day. Because levels fluctuate constantly, the reading must be measured over three months with two detectors to give an accurate picture of the year round exposure. UKHSA recommends reducing radon levels in homes where the average is more than 200 becquerels per cubic metre.
There is also a lower threshold known as the target level, which is set at 100 becquerels per cubic metre. This is the ideal outcome for remediation in existing buildings. If you have work done to lower a high reading, the target level is the ideal outcome.
Results between the target and action levels warrant considering action. This is especially true if someone in the home smokes or has smoked.
How a radon test works
The standard measurement service involves placing two small, discreet detectors in your home. You place one detector in the main living area and the second detector in an occupied bedroom.
The detectors are posted out to you and returned afterwards. Follow the instructions that come with them.
The test is carried out over three months to allow for variations in levels. Levels vary, which is why the test runs for three months.
A short test would not allow for those variations. At the end of the three months, you return the detectors.
The only way to know if a building has a high radon level is to have it tested. Indoor radon often varies from building to building in the same area, so you cannot rely on a neighbour's low reading to prove your home is safe. If you rent your property, tenants should speak to their landlord, who should arrange a test.
What a radon test costs
At the time of writing, the UKHSA radon measurement service costs £52.80 including VAT. The page is undated, so check the current price.
If you only want to check the estimated probability for a specific property before committing to a full three month test, you can order a Radon Risk Report. At the time of writing, this address search report costs £3.90 including VAT.
If your result is high
If your three month test shows an annual average above the action level, UKHSA recommends reducing radon levels. The ideal outcome for remediation in existing buildings is to reach the target level of 100 becquerels per cubic metre.
There are several ways to reduce radon. UKHSA calls an active sump with a fan the most effective way to reduce indoor radon.
Other options named are a passive sump with no fan, natural or active under-floor ventilation and positive ventilation. The right one depends on the home, and a competent contractor can advise.
The table below shows the typical cost and normal range for contractor installed remedies, using averages from data collected between 2007 and 2017.
|
Remedy |
Typical cost, 2007 to 2017 data |
Normal range |
|---|---|---|
|
Active sump with fan |
£800 |
Up to £2,000 |
|
Passive sump (no fan) |
£450 |
Up to £1,000 |
|
Natural under-floor ventilation |
£200 |
Up to £600 |
|
Active under-floor ventilation |
£700 |
Up to £1,500 |
|
Positive ventilation |
£550 |
Up to £1,000 |
These are averages from data collected between 2007 and 2017, so current quotes may be higher. Use a competent contractor to install these systems and do not attempt DIY radon work.
Radon when you buy or sell a home
The issue of radon comes up when buying and selling properties, and conveyance documents ask questions about radon.
If the property sits in an Affected Area, the buyer will want to know if it has been tested. Because indoor radon often varies from building to building in the same area, a buyer cannot assume the house is clear just because the wider street seems fine. The only way to know if a building has a high radon level is to have it tested.
A test is carried out over three months to allow for variations in levels, so ask your conveyancer early whether the home has been tested.
If the seller has no test result, ask your conveyancer what your options are.
What a surveyor can and cannot tell you about radon
A standard home survey is a detailed visual inspection of a property's physical condition. It is not a radon test. A surveyor uses their eyes and professional tools to find structural defects, but they cannot see, smell or taste a radioactive gas.
While a surveyor will look for common problems house surveys find like damp, timber decay or subsidence, they will not carry out gas measurements. Ask the surveyor what they will comment on regarding radon.
Ask your conveyancer whether the home has been tested. It is worth knowing the right questions to ask a surveyor before you instruct them, so you understand exactly what their report will cover.
If the home already has a radon system, ask whether the surveyor will comment on it.
Common questions
What is radon gas and where does it come from?
Radon is a natural radioactive gas from rock and soil. It is colourless, odourless and tasteless, meaning you cannot tell it is there without a test. It can build up inside buildings.
Can I get a quick radon survey before buying a house?
The UKHSA measurement is carried out over three months to allow for variations in levels, so it does not fit a quick purchase. Indoor radon often varies from building to building in the same area, so ask your conveyancer whether the home has been tested.
Can I use the radon map for a basement?
No. The UKHSA map should not be used for basements, cellars or underground sites. The only way to know if a building has a high radon level is to have it tested.
Is a radon test a legal requirement for homeowners?
UKHSA advises testing if you live or work in an Affected Area, which is advice rather than a rule. Tenants should speak to their landlord, who should arrange a test. Conveyance documents also ask questions about radon when you buy or sell a home.
Does a standard house survey check for radon gas?
A standard house survey is a visual inspection of the property condition and is not a radon test. A surveyor cannot see or smell radon gas. Ask what the surveyor will comment on, and ask your conveyancer whether the home has been tested.
What is the radon action level?
UKHSA recommends that radon levels should be reduced in homes where the average is more than 200 becquerels per cubic metre, and the Government has endorsed this. The level refers to the annual average, measured over three months with two detectors.
What is the target level?
The target level is 100 Bq/m3, the ideal outcome for remediation in existing buildings. Results between the target and action levels warrant considering action, especially if someone in the home smokes or has smoked.
Does the radon map tell me the level in my own home?
No. The map shows the chance of a higher level, and a radon address search report gives the estimated probability of a property being above the action level. Only a test shows the level in a particular building.
How much does fixing a high reading cost?
The table above gives averages from data collected between 2007 and 2017, so current quotes may be higher. A competent contractor can quote for your home.
What does a radon test cost?
At the time of writing, the UKHSA measurement service is £52.80 including VAT and a Radon Risk Report is £3.90 including VAT. The pages are undated, so check the current prices before you order.
Who arranges a radon test in a rented home?
Tenants should speak to their landlord, who should arrange a test. UKHSA advises testing if you live or work in an Affected Area.
What to do next
If you are buying a home or living in an area you suspect is affected by radon, taking action is straightforward. Follow these steps to protect your household and keep your property transaction moving.
- Check the official radon map to see if the property is in an Affected Area.
- Order an address search report if the map shows a darker colour over the property.
- Ask your conveyancer if the current owner has a recent test result.
- Speak to your landlord about arranging a test if you rent the property.
- Order a three month measurement service if testing falls to you.
If you are buying a property and need a professional to assess its overall condition, you can use our directory to find a surveyor near you.
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