Radon Certificate When Selling Your Property

Radon is a naturally occurring radioactive gas that seeps into buildings from the ground. In certain parts of the UK, particularly areas with granite and limestone bedrock, radon concentrations in homes can exceed levels that the UK Health Security Agency (UKHSA) considers safe for long-term exposure. When you sell a property in one of these areas, the buyer's solicitor, surveyor, or mortgage lender is very likely to raise radon as a concern — and a radon certificate is the document that answers their questions.

This guide explains what a radon certificate is, when you need one for a property sale, how to get tested, what the results mean, and how to handle situations where your radon levels are above the recommended threshold. For a broader look at how elevated radon affects the sale process, see our guide on selling a house with high radon levels.

What is a radon certificate?

A radon certificate is the formal results report issued after a radon test has been carried out in a property. It is not a government-mandated certificate like an Energy Performance Certificate, but rather a laboratory-issued document that records the measured radon concentration in your home over a defined period.

The standard certificate comes from the UKHSA radon testing service (formerly Public Health England) or from a UKAS-accredited laboratory. It typically includes:

• The property address
• The rooms where detectors were placed (usually the main living room and a bedroom)
• The measurement period (standard tests run for three months)
• The average radon concentration in becquerels per cubic metre (Bq/m³)
• A statement of whether the result is above or below the UK action level of 200 Bq/m³

If remediation work has been carried out and a follow-up test performed, you may also have a post-mitigation certificate confirming that radon levels have been reduced to below the target level of 100 Bq/m³. Together, these documents demonstrate that the radon risk has been identified and managed.

When is a radon certificate needed for selling?

There is no legal obligation to provide a radon certificate when selling a property in England and Wales. It is not included in the list of property certificates that are legally mandated. However, in practice, you are likely to need one if any of the following apply:

• Your property is in a radon-affected area. UKHSA classifies areas based on the percentage of homes estimated to exceed the action level. If more than 1% of homes in your postcode area are estimated to be above 200 Bq/m³, it is considered a radon-affected area and the issue will almost certainly be raised during conveyancing.
• The environmental search flags radon risk. The buyer's solicitor will typically order an environmental search as part of the standard search pack. If the search identifies the property as being in a radon-affected area, the solicitor will raise a formal enquiry about radon.
• The surveyor raises radon as a concern. A surveyor carrying out a RICS HomeBuyer Report or Building Survey in a radon-affected area will typically note the radon risk in their report and recommend that a test be carried out if one has not already been done.
• The mortgage lender requires it. Some mortgage lenders make a radon test a condition of the mortgage offer for properties in high-risk areas, particularly if the survey or environmental search has highlighted the issue.
• You have previous test results to disclose. If you have had a radon test done and know the results, you are expected to disclose them on the TA6 Property Information Form. A certificate showing low results is a positive disclosure. A certificate showing high results with evidence of mitigation is still better than no information at all.

How to get a radon certificate

The process for obtaining a radon certificate is straightforward, but it does take time. The standard three-month test is the version most widely accepted during conveyancing.

Step 1: Order detectors

Order a pair of passive radon detectors from the UKHSA radon testing service or from a UKAS-accredited laboratory. The cost is approximately £50 to £60, which includes the detectors, laboratory analysis, and the results certificate.

Step 2: Place detectors

Place one detector in the main living room and one in a bedroom. The detectors should be positioned away from draughts, heat sources, and direct sunlight. Follow the instructions provided with the detectors carefully, as incorrect placement can affect the accuracy of results.

Step 3: Leave in place for three months

The three-month measurement period is designed to account for natural fluctuations in radon levels caused by weather conditions, heating patterns, and ventilation. Shorter screening tests are available, but they provide a less reliable snapshot and may not be accepted by the buyer's solicitor or mortgage lender.

Step 4: Return detectors for analysis

After three months, return the detectors to the laboratory in the pre-paid envelope provided. Results are typically issued within two to four weeks. The results certificate is your radon certificate — keep it safe with your property documents.

Timing for sellers

Because the standard test takes three months plus analysis time, planning ahead is essential. If you know you are going to sell and your property is in a radon-affected area, ordering the test before you instruct an estate agent avoids the risk of a three-month delay once a buyer is found. If you already have results from a test within the last five years, these are generally accepted without the need for a fresh test.

Understanding radon levels and what they mean for your sale

The UKHSA uses two key thresholds when assessing radon risk in homes:

Results between 100 and 200 Bq/m³ fall in a grey area. They are below the action level, so remediation is not formally recommended by UKHSA, but they are above the target level. Some buyers and their solicitors may accept these results without further action; others may request remediation or ask for a price reduction. Having the certificate available for discussion is always better than having no data at all.

Radon and the TA6 Property Information Form

The TA6 Property Information Form includes questions about environmental matters affecting the property. If you have had a radon test, you are expected to disclose the results. This falls under the seller's general duty not to withhold material information that could affect the buyer's decision.

When completing the TA6, you should:

• Confirm whether a radon test has been carried out and, if so, provide the certificate
• If levels exceeded 200 Bq/m³, state what mitigation was installed and provide the post-mitigation test results
• If no test has been done and you are not aware of any radon issue, state this honestly — you are not required to test if you have no reason to believe there is a problem
• If the property has a radon mitigation system, provide details of the system, the installer, and any maintenance records

Deliberately concealing known radon results could expose you to a misrepresentation claim under the Consumer Protection from Unfair Trading Regulations 2008 and the Misrepresentation Act 1967. Full disclosure with supporting documentation is always the safer approach.

What to do if radon levels are above the action level

If your radon certificate shows a concentration above 200 Bq/m³, you have several options. The right approach depends on your timescale and whether you want to resolve the issue before marketing or negotiate with the buyer.

Option 1: Install mitigation before listing

This is the recommended approach. The most common and effective remediation method is a radon sump system, which involves installing a small sump beneath the floor connected to a low-powered electric fan. The fan draws radon-laden air from beneath the building and vents it safely above the roofline. A radon sump typically costs between £800 and £2,000 including installation and can usually be fitted within one to two days.

After installation, a follow-up test (either a three-month test or a shorter screening period) is carried out to confirm that levels have dropped below 100 Bq/m³. The post-mitigation certificate, together with documentation of the system installed, provides a complete package for the buyer's solicitor.

Option 2: Positive input ventilation

A positive input ventilation (PIV) system draws filtered air into the property from the loft, creating slight positive pressure that inhibits radon ingress. PIV systems cost between £500 and £1,200 installed. They are less effective than a radon sump for very high concentrations but can be appropriate where levels are moderately above the action level.

Option 3: Negotiate with the buyer

If you do not wish to carry out remediation yourself, you can disclose the radon results and allow the buyer to factor the cost of mitigation into their offer. This approach is transparent but comes with risks: the buyer may overestimate the cost, use it as a negotiation lever for a larger reduction, or withdraw altogether. Providing quotes from reputable contractors helps to set realistic expectations.

Option 4: Indemnity insurance

Indemnity insurance is not typically used for radon in the way it is for missing building control certificates. Radon is a measurable, testable condition, and buyers and lenders generally expect a test result rather than an insurance policy. However, if the property is in a borderline area and no test has been done, your solicitor may advise on whether any form of environmental indemnity is appropriate.

Radon mitigation costs at a glance

How radon comes up during conveyancing

Radon can surface at several points during the conveyancing process. Understanding when and how it arises helps you prepare in advance.

1. Environmental search. The buyer's solicitor orders an environmental search which checks for contaminated land, flood risk, and radon probability. If the search indicates the property is in a radon-affected area, a formal enquiry is raised.
2. TA6 disclosure. When answering the TA6 form, you will need to address questions about environmental matters. If you have test results, provide them. If not, state that no test has been done.
3. Surveyor's report. A RICS surveyor working in a radon-affected area will typically note the radon risk and recommend testing if no certificate has been provided.
4. Mortgage lender conditions. If the surveyor's report or the environmental search flags radon, the lender may add a condition requiring a satisfactory radon test before releasing funds.
5. Buyer's solicitor enquiries. Even if none of the above trigger a requirement, a thorough solicitor in a radon-affected area may raise radon as a standard additional enquiry.

Having a radon certificate ready before any of these triggers arise is the most effective way to prevent delays. A three-month test started before marketing means the results are available by the time the buyer's solicitor raises the question.

Radon-affected areas and the UKHSA map

UKHSA publishes an interactive online radon map that estimates the probability of homes exceeding the action level by postcode. The map is based on geological data and thousands of radon measurements collected over several decades. It is the definitive reference used by surveyors, solicitors, and environmental search providers.

The areas with the highest radon levels in England and Wales include:

• Cornwall and Devon — granite bedrock produces the highest radon concentrations in the UK. In parts of Cornwall, more than 30% of homes exceed 200 Bq/m³.
• Somerset and Dorset — limestone geology contributes to elevated levels, particularly in the Mendip Hills area.
• Derbyshire and the Peak District — carboniferous limestone produces significant radon levels in many properties.
• Northamptonshire — ironstone geology creates radon-affected areas, particularly in the north and west of the county.
• Parts of Wales — Powys and Gwynedd have notable radon concentrations due to underlying geology.

If you are selling a property in any of these areas, obtaining a radon certificate before marketing is strongly advisable. Even in areas where the overall probability is lower, individual properties can have elevated levels because radon distribution is highly localised.

Radon in new-build properties

Properties built after 1999 in radon-affected areas should have been constructed with radon protection measures as required by Building Regulations (Approved Document C). These measures may include a radon-proof membrane across the ground floor and, in higher-risk areas, a radon sump ready for activation if levels prove to be elevated after occupation.

If you are selling a relatively new property in a radon-affected area, check whether radon protection was included in the original construction. Your building control completion certificate and the building specification should confirm this. Even with built-in protection, a radon test provides concrete evidence that the measures are working effectively.

Sources

• UK Health Security Agency (UKHSA) — Radon: properties, health effects, and reducing levels in your home — gov.uk
• UKHSA interactive radon map — ukradon.org
• Building Research Establishment (BRE) — Radon: guidance on protective measures for new buildings (BR 211) — bregroup.com
• Approved Document C: Site preparation and resistance to contaminants and moisture — gov.uk
• World Health Organisation — WHO handbook on indoor radon: a public health perspective — who.int
• Consumer Protection from Unfair Trading Regulations 2008 — legislation.gov.uk
• Law Society — TA6 Property Information Form, 4th edition

Frequently asked questions