Radon and buying a house

Radon is a natural radioactive gas from rocks and soils that can build up indoors, and long-term exposure increases the risk of lung cancer. If you are buying in a radon affected area, check the property's risk, ask the seller whether it has been tested or has protective measures, and plan to test after you move in if needed. High levels can usually be reduced with fairly straightforward work.

Key points

• Radon is colourless and odourless, so testing is the only way to know the level in a home.
• UKHSA's action level for homes is 200 Bq/m3, with a target level of 100 Bq/m3.
• Risk varies by geology, with parts of the South West, Wales, the Peak District and Northamptonshire among the higher risk areas.
• A standard radon test takes three months.
• Remedial measures such as a radon sump are usually effective.

What is radon and why does it matter?

Radon is a radioactive gas produced by the decay of uranium, which is present in small amounts in all rocks and soils. Outdoors it disperses harmlessly, but it can enter buildings through cracks in floors, gaps around pipes and cavities, and build up indoors.

The UK Health Security Agency (UKHSA) identifies radon as the second biggest cause of lung cancer after smoking. The risk is much higher for smokers and ex-smokers exposed to radon.

Which areas are affected?

Radon levels vary widely depending on geology. Higher levels are more common in areas with granite and some limestone and ironstone geology, such as parts of Cornwall and Devon, Wales, Derbyshire, Northamptonshire and parts of northern England. But radon can be high in individual homes anywhere, and two neighbouring homes can have very different levels.

A radon affected area is one where 1% or more of homes are estimated to have levels above the action level. Within those areas, the probability for each property varies.

How do you check the radon risk of a property?

1. UKHSA radon maps and address search. UKHSA provides indicative radon maps for free and an address-level radon risk report for a small fee, for England and Wales.
2. Environmental search. Your conveyancer's environmental search usually includes radon risk.
3. Ask the seller. The TA6 property information form asks whether a radon test has been carried out, the result, and whether radon remedial measures have been installed.
4. Building Regulations. New homes in higher risk areas should have radon protection, such as a membrane in the ground floor. Ask the developer or check building control records.

What do the action and target levels mean?

Radon is measured in becquerels per cubic metre (Bq/m3).

• Action level: 200 Bq/m3. UKHSA recommends taking action to reduce radon if the annual average in a home is above this.
• Target level: 100 Bq/m3. The ideal outcome of remedial work. UKHSA also recommends that homeowners with levels between 100 and 200 consider reducing them, particularly if they smoke.

Does a house survey check for radon?

No, not directly. A surveyor carrying out a Level 2 Home Survey or Level 3 Building Survey does not test for radon. Some surveyors note if the property is in a known radon area, or if a radon sump is visible, and may recommend that your conveyancer checks the radon risk. Radon is usually picked up through searches and the seller's answers.

How do you test for radon?

The standard test uses two small passive detectors, one in an occupied bedroom and one in a living area, left for three months to account for daily and seasonal variation. They are then posted back to a laboratory for analysis. Shorter tests exist but are less reliable for long-term average exposure.

Because the test takes three months, it is rarely possible to complete before exchange. Options include:

• Asking whether the seller has a recent test result.
• Agreeing to test once you have moved in and budgeting for possible remedial work.
• Negotiating a price reduction if the property is in a high risk area with no protective measures.

How do you reduce radon levels?

Common remedial measures include:

• Radon sump - a small cavity beneath the floor with a pipe and fan that draws radon out and vents it outside. Usually very effective for solid floors.
• Improved underfloor ventilation - for suspended timber floors, adding or clearing air bricks, or fitting a fan.
• Positive ventilation - a fan system that pushes air into the home.
• Sealing cracks and gaps in floors, usually alongside other measures.

Costs vary by method and property. Improved ventilation is often the cheaper option, while a sump installation costs more but is very effective. Get a quote from a specialist radon contractor, and retest afterwards to confirm the result.

What should you ask if a radon sump is already fitted?

A visible radon sump, with a pipe and fan venting outside, is a good sign that the risk has been addressed. Before you buy, ask:

• When was it installed, and by whom?
• What were the radon readings before and after installation?
• Is the fan still working, and when was it last checked? Fans run continuously and need replacing eventually.
• Are there any guarantees or service records?

If there are no post-installation results, plan to retest once you have moved in to confirm the system is working. Running costs for a sump fan are usually low, but it is worth knowing the fan's age so you can budget for a replacement.

Does radon affect the value or mortgage?

Radon rarely affects lending, and it is common for buyers in affected areas to test after moving in. If the seller has a high result with no remedial work, it is reasonable to factor the cost into your offer. See our guide to renegotiating after a survey.

Radon and other ground risks

Areas with high radon sometimes overlap with former mining areas. See our guide to buying in a former coal mining area. Flood risk is another environmental risk to check. See flood risk before you buy.

If you are buying anywhere in England or Wales and want a local surveyor to look at the property, get a fixed-price survey booked. See how it works.

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