Radon Test When Selling a House: Is It Required?

Radon is a colourless, odourless radioactive gas produced by the natural decay of uranium in rocks and soil. It seeps into buildings through cracks in floors, gaps around pipes, and other openings in the ground floor or basement. According to the UK Health Security Agency (UKHSA), radon is responsible for around 1,100 lung cancer deaths per year in the UK, making it the second largest cause of lung cancer after smoking.

If you are selling a property in a radon-affected area, you may be wondering whether you need to test, what the results could mean for your sale, and what you are legally required to disclose. This guide covers everything sellers need to know about radon, from testing and remediation through to how it appears in the conveyancing process.

Is a radon test legally required when selling?

No. There is no law in England and Wales that requires a seller to carry out a radon test before putting their property on the market. Unlike an Energy Performance Certificate, which is a legal requirement before marketing a property, radon testing is entirely voluntary.

However, that does not mean you can ignore radon altogether. If your property is in an area where radon is known to be present, the buyer's solicitor is very likely to raise it as part of their conveyancing enquiries, and the environmental search results will flag the property's radon risk. If you already know about a radon issue — because you have had a test or carried out remediation — you are expected to disclose it on the TA6 Property Information Form.

In practice, testing proactively is strongly recommended if your property is in a radon-affected area. Having results available from the outset puts you in a much stronger position than waiting for the buyer's solicitor to raise concerns partway through the transaction.

Understanding radon levels: action level and target level

The UKHSA (formerly Public Health England) sets two key reference points for radon in UK homes:

• Action level: 200 Bq/m³. If the average radon concentration in your home is at or above 200 becquerels per cubic metre, the UKHSA recommends taking action to reduce it. This is the level at which remediation is strongly advised.
• Target level: 100 Bq/m³. This is the goal for any remediation work. The UKHSA recommends that remediation should aim to reduce radon levels as far below the target level as reasonably practicable. It is also the reference level recommended by the World Health Organisation.

For context, the average indoor radon level across the UK is approximately 20 Bq/m³. However, in radon-affected areas, individual properties can have levels many times higher than this, depending on the underlying geology, construction type, and ventilation.

From a selling perspective, a result below the target level of 100 Bq/m³ is reassuring to buyers and their solicitors. A result between 100 and 200 Bq/m³ may prompt questions but is unlikely to cause serious problems. A result at or above the action level of 200 Bq/m³ will almost certainly require remediation before a buyer proceeds, particularly if they are purchasing with a mortgage.

Which areas of the UK are affected by radon?

Radon levels vary dramatically across the UK, driven primarily by the underlying geology. The UKHSA publishes an interactive radon map that shows the estimated percentage of homes exceeding the action level in any given area, searchable by postcode. The areas with the highest radon levels include:

• South-west England: Cornwall, Devon, Somerset, and parts of Dorset have some of the highest radon levels in the UK. In parts of Cornwall, over 30% of homes exceed the action level.
• Peak District and Derbyshire: The limestone geology of Derbyshire and the surrounding area produces significant radon levels.
• Northamptonshire: Parts of Northamptonshire, particularly around the ironstone belt, have elevated radon levels.
• Parts of Wales: Powys and Gwynedd in particular have areas with high radon concentrations.
• Other affected areas: Parts of the Scottish Highlands, the Yorkshire Dales, Somerset, and Oxfordshire also have elevated levels in certain locations.

The UKHSA defines a radon-affected area as one where 1% or more of existing homes are estimated to have radon levels at or above the action level. Within these broader areas, the actual risk varies significantly from one property to the next, which is why individual testing is the only reliable way to know your property's radon level.

How to test for radon

The recommended and most widely accepted method of radon testing in the UK is a three-month passive detector test, available directly from the UKHSA radon services team. Here is how it works:

1. Order detectors. Contact UKHSA radon services and order a pair of passive radon detectors. The cost is approximately £50 to £60, which includes analysis and a results report.
2. Place the detectors. Put one detector in your main living room and one in a bedroom you regularly use. They should be placed on a shelf or similar surface, away from draughts and heat sources.
3. Leave for three months. The detectors need to remain in place for a full three months to account for daily and seasonal fluctuations in radon levels. The best time to test is during the heating season (October to March), when radon levels tend to be highest because windows and doors are kept closed.
4. Return for analysis. After three months, post the detectors back to the UKHSA laboratory. Results are typically available within a few weeks.
5. Receive your report. The report gives the average radon concentration for each room and an overall seasonal corrected result, expressed in Bq/m³.

Short-term screening devices and electronic radon monitors are available for quicker results, but they provide a less accurate snapshot and may not be accepted by a buyer's solicitor as definitive. If you are planning to sell a property in a radon-affected area, the three-month test is the gold standard. Start it well before you intend to list.

Radon remediation: options and costs

If your test reveals radon levels at or above the action level of 200 Bq/m³, remediation is strongly recommended — both for health reasons and to facilitate the sale. The BRE (Building Research Establishment) publishes detailed guidance on remediation methods in its report BR 211. The main options are:

Radon sump (active sump system)

A radon sump is the most effective remediation method for most properties. It works by creating a collection point beneath the ground floor of the building, connected by a pipe to a low-powered fan that draws radon-laden air from under the building and vents it safely above the roofline. A properly installed and functioning radon sump can reduce indoor radon levels by up to 90%.

The typical cost is £800 to £1,500 including installation. The fan runs continuously and uses very little electricity — approximately £20 to £40 per year. Installation usually takes one to two days with minimal disruption.

Positive input ventilation (PIV)

A PIV unit is installed in the loft space and gently pushes filtered air into the property, creating a slight positive pressure that prevents radon from being drawn in through the ground floor. PIV is effective where radon levels are moderately elevated (typically up to around 500 Bq/m³) and has the added benefit of reducing condensation and improving general air quality.

The typical cost is £500 to £1,000 installed. Running costs are similar to the sump fan — around £20 to £40 per year.

Improved underfloor ventilation

For properties with suspended timber floors over a ventilated void, improving natural ventilation by adding or clearing airbricks can help reduce radon levels. This is the least expensive option (typically under £500) but is generally less effective than a sump or PIV system and may not be sufficient for properties with high radon levels.

After any remediation work, you should carry out a follow-up radon test to confirm that levels have been reduced below the target level of 100 Bq/m³. This follow-up result is valuable evidence to provide to a buyer.

How radon appears in the conveyancing process

Radon can come up at several points during the conveyancing process. Understanding where and how it is raised helps you prepare effectively.

Environmental search results

The buyer's solicitor will order an environmental search as a standard part of the conveyancing process. This search checks the property against various environmental datasets, including radon data from the UKHSA. If the property is in a radon-affected area, the search will flag this, often with an estimated probability that the property exceeds the action level. This typically triggers further enquiries.

TA6 Property Information Form

The environmental section of the TA6 form asks whether you are aware of any environmental issues affecting the property. If you have had a radon test, you should disclose the results here. If remediation has been carried out, provide details of the system installed, the installer, and any follow-up test results. Honest disclosure protects you from future misrepresentation claims. For a full overview of what you need to declare, see our guide on what to disclose when selling a house.

Buyer's conveyancing enquiries

If the environmental search flags a radon risk, the buyer's solicitor will typically raise additional enquiries asking whether a radon test has been carried out, what the results were, and whether any remediation has been done. If you have a test result and remediation evidence ready, you can answer these enquiries quickly. If not, the buyer may request that you carry out a test before they proceed, which adds at least three months to the timeline.

Mortgage lender requirements

There is no blanket requirement from UK mortgage lenders for radon testing. However, if the surveyor's valuation report or the environmental search highlights a significant radon risk, the lender may impose conditions — such as requiring a radon test or retention of funds until remediation is complete — before releasing the mortgage. This is more common with properties in the highest-risk areas.

Building Regulations and radon in new builds

While there is no requirement for sellers of existing properties to test for radon, Building Regulations in England and Wales (Approved Document C) do require radon protective measures in new buildings located in radon-affected areas. The level of protection depends on the estimated radon risk for the site:

• Low-risk areas (under 3%): No radon-specific measures are required beyond standard damp-proofing.
• Intermediate areas (3% to 10%): A basic radon barrier (a continuous membrane across the ground floor) must be installed.
• High-risk areas (over 10%): Both a radon barrier and provision for a radon sump (a sump installed but without a fan, ready to be activated if monitoring shows it is needed) are required.

These requirements are set out in the BRE report BR 211 and apply to new dwellings, extensions, and conversions. If you are selling a relatively new property in a radon-affected area, checking whether these protective measures were installed as part of the original build can be a useful selling point. The details should be available in the building control completion certificate or the original building plans.

Impact of radon on your sale

Radon is unlikely to prevent you from selling your property, but it can affect the sale in several ways if it is not handled proactively:

• Delays. If a buyer's solicitor raises radon concerns and you have no test result, the buyer may request a three-month test before proceeding. This can add significant time to an already lengthy conveyancing process.
• Price renegotiation. If high radon levels are discovered during the transaction, the buyer may ask for a reduction in the sale price to cover the cost of remediation, typically £800 to £1,500 for a radon sump.
• Buyer withdrawal. In the worst case, a buyer who is alarmed by radon concerns and unsure of the implications may withdraw entirely. This is more likely with buyers unfamiliar with radon-affected areas.
• Mortgage complications. If the lender imposes conditions related to radon, such as a retention or a requirement for remediation before completion, this adds complexity and delay.

The most effective strategy is straightforward: if you are in a radon-affected area, test before you sell, remediate if necessary, and have the documentation ready for your buyer. A clear radon test result or evidence of successful remediation removes radon as an obstacle entirely.

Practical steps for sellers in radon-affected areas

1. Check the UKHSA radon map. Enter your postcode on the UKHSA interactive radon map to see whether your property is in a radon-affected area. If fewer than 1% of homes in your area are estimated to exceed the action level, radon is unlikely to be an issue.
2. Order a three-month test early. If your property is in an affected area, order detectors from UKHSA radon services at least four to five months before you plan to list. This gives you time to receive results and arrange remediation if needed.
3. Remediate if above the action level. If your results are at or above 200 Bq/m³, arrange for a radon sump or other appropriate remediation. Keep all invoices, installation certificates, and warranty documentation.
4. Carry out a follow-up test. After remediation, run another three-month test to confirm levels are below the target level of 100 Bq/m³. This evidence is exactly what a buyer's solicitor will want to see.
5. Disclose honestly on the TA6. Include your radon test results and remediation details in your TA6 answers. Provide copies of test reports and remediation certificates as part of your sale documentation pack.
6. Brief your solicitor. Make sure your solicitor has all the radon-related documentation so they can respond to buyer enquiries promptly without needing to come back to you.

Sources

• UK Health Security Agency (UKHSA) — UK radon map and guidance on radon in homes (previously published by Public Health England)
• BRE (Building Research Establishment) — BR 211: Radon: guidance on protective measures for new buildings
• HM Government — Approved Document C: Site preparation and resistance to contaminants and moisture (Building Regulations)
• GOV.UK — Radon: properties affected and what you should know
• World Health Organisation — WHO handbook on indoor radon: a public health perspective (2009)
• Law Society — TA6 Property Information Form (4th edition, 2020)

Frequently asked questions