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Radon gas UK: Risks, testing and buying a home

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Clare Lowes

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Radon gas UK: Risks, testing and buying a home

Radon has an awkward habit of appearing when a house purchase already feels complicated enough.

The environmental search arrives, one line refers to a “Radon Affected Area”, and suddenly the home you had been picturing yourself living in appears to come with an invisible radioactive gas beneath the floorboards.

I can understand why that wording causes alarm. Radon cannot be seen, smelled or tasted, and anything involving radiation sounds immediately threatening. The more reassuring truth is that a radon search result is not a diagnosis of the property. It identifies a possibility that can be measured and, where necessary, usually reduced.

Quick answer: Radon is a naturally occurring radioactive gas that can enter buildings from the ground. Long-term exposure to elevated levels increases the risk of lung cancer, particularly for smokers and former smokers. A search can show whether a home is in a Radon Affected Area, but only a measurement inside the property can establish its radon level. UKHSA recommends action where the annual average is at or above 200 becquerels per cubic metre and identifies 100 Bq/m³ as the Target Level.

Finding radon risk during conveyancing is not normally a reason to abandon a purchase. It is a reason to establish what is known, arrange appropriate testing and agree who will pay if reduction work is required.

This guide concentrates on homes in England and Wales, although the UK radon Action and Target Levels apply more widely.

Contents

What is radon gas?

Radon is a naturally occurring radioactive gas formed as small amounts of uranium in rocks and soil decay.

It is colourless, odourless and tasteless. There is no physical warning that a building contains an elevated level, which is why measurement is necessary.

Radon is present in the atmosphere everywhere. Outdoors, it normally disperses and concentrations remain low. Inside a building, gas entering from the ground can become trapped and accumulate.

The ground is usually the principal source. Radon levels therefore vary according to local geology, the construction and condition of the building, ventilation, weather and how the property is occupied.

Two neighbouring houses can produce quite different results. One may have a low reading while the other exceeds the Action Level because of differences in foundations, floors, extensions or airflow.

The official UKradon service operated by the UK Health Security Agency summarises the practical approach as: Check, measure and act.

Why is radon a health risk?

Radon itself decays into tiny radioactive particles. When inhaled, those particles can lodge in the airways and emit radiation that damages lung tissue.

This is not normally an immediate poisoning risk. Radon does not usually cause short-term symptoms that alert somebody to its presence. The concern is prolonged exposure and the increased lifetime risk of lung cancer.

UKHSA estimates that radon contributes to more than 1,100 lung-cancer deaths each year in the UK.

The risk rises with the radon concentration and length of exposure. It is substantially greater for smokers because smoking and radon both damage the lungs. Former smokers also remain at greater risk than people who have never smoked, although stopping smoking significantly reduces the overall risk.

This is an important point of perspective. Most UK homes have comparatively low radon levels, and discovering that a property lies within a risk area does not mean that its occupants will develop cancer.

It means that the possibility of higher long-term exposure should be checked rather than ignored.

UKHSA explains the evidence and relative risks in its guidance on the health risks associated with radon.

What are the UK radon Action and Target Levels?

Radon concentration in air is measured in becquerels per cubic metre, written as Bq/m³.

The Action Level: 200 Bq/m³

The UK radon Action Level is an annual average concentration of 200 Bq/m³.

Where a home produces a result at or above that level, UKHSA recommends taking steps to reduce the concentration.

The Action Level should not be misunderstood as a boundary between completely safe and dangerous air. Radon risk increases gradually with exposure rather than beginning suddenly at 200 Bq/m³.

The Target Level: 100 Bq/m³

The Target Level is 100 Bq/m³. This is the ideal outcome for remedial work in an existing home and for protective measures incorporated into a new building.

Where a result lies between 100 and 200 Bq/m³, reducing the level should be considered, particularly where an occupant is a smoker or former smoker.

A result below 100 Bq/m³ is below the UK Target Level. It does not mean that the air contains no radon, but formal reduction work will not normally be advised purely because of that reading.

The distinction is set out in the official guidance on radon Action and Target Levels.

What is a Radon Affected Area?

A Radon Affected Area is an area where at least 1% of homes are estimated to have an annual average radon concentration at or above the Action Level.

The classification describes probability, not the actual reading inside every property.

For example, a search result may indicate that between 3% and 5% of homes in the locality are expected to exceed 200 Bq/m³. That does not mean that the property contains a concentration of 3%, 5% or any other measured amount. It means that homes in that risk band have that estimated chance of exceeding the Action Level.

Some of the best-known higher-risk areas are in Cornwall, Devon and other parts of south-west England, where the geology contains more uranium-bearing rock. Radon Affected Areas are not confined to the South West, however. They occur in parts of Wales, the Midlands, the Pennines and elsewhere.

Regional generalisations are not sufficiently precise for a property purchase. The free national map provides a broad indication, while a paid address report gives the estimated probability for the particular address.

You can view the national information or obtain an individual UKHSA Radon Risk Report.

The report still does not measure the home. Its result is the estimated likelihood that the property exceeds the Action Level.

How does radon enter a home?

Buildings naturally draw some air from the ground beneath them. If that ground contains radon, the gas can enter through small openings in the structure.

Possible entry routes include:

  • cracks in solid floors;
  • gaps around pipes and other services;
  • construction joints;
  • poorly ventilated suspended floors;
  • cellars and basements; and
  • openings created during later alterations.

The amount entering the property is influenced by pressure differences between the building and the soil, together with the floor construction and ventilation arrangements.

Sealing visible cracks may form part of a reduction scheme, but it should not be assumed that sealing alone will solve a significant radon problem. Gas can find several routes into a building, some of which are not visible.

In a small number of homes, particularly those with a private groundwater supply, radon dissolved in water may contribute to the indoor concentration. UKHSA provides separate guidance on radon and private water supplies.

Which properties have a higher radon risk?

Location is important, but it is not the only factor.

Rooms at or below ground level have more direct contact with the source. Basements, cellars, converted lower-ground floors and houses built into slopes therefore deserve particular attention.

UKHSA recommends measuring every occupied basement that is used for more than 50 hours a year, regardless of the property’s mapped radon probability.

Ground-floor rooms are generally more exposed than upper floors. A flat several storeys above the ground may consequently have a lower likelihood of an elevated reading, although the construction and airflow of the building still matter.

Older houses are not automatically more dangerous than new ones. An older property may be draughtier and naturally ventilated, while modern insulation and draughtproofing can alter how air moves through a home.

Extensions, new windows, insulation, heating changes and the conversion of a basement can all affect the concentration. A historic test result should therefore be considered in the context of any significant work completed since the measurement.

Radon searches and tests: What is the difference?

This distinction is the most important practical point for a buyer.

A radon search estimates risk

A radon search uses geological information and previous property measurements to place the address within a probability band.

It may say that the home lies outside a Radon Affected Area or that a stated percentage of properties in the area are estimated to exceed the Action Level.

It does not sample the air and cannot tell you the radon concentration inside the home.

A radon test measures the property

A radon measurement uses detectors placed inside the occupied building. The result estimates the annual average concentration in Bq/m³.

That is the information needed to decide whether radon-reduction work should be considered or recommended.

A useful way to think about the distinction is that the search answers:

“How likely is this address to have an elevated level?”

The measurement answers:

“What is the estimated annual average level inside this particular home?”

How does radon arise during conveyancing?

Radon information may appear through several parts of the conveyancing investigation.

The local authority search includes questions relating to whether the property is in a Radon Affected Area. An environmental search will also commonly include a radon-risk assessment.

The seller’s Property Information Form asks about radon, including previous testing and any protective or remedial measures installed at the property.

These sources should be considered together. A search might identify the area as affected while the seller supplies a satisfactory measurement made under normal occupancy conditions. Alternatively, the seller may never have tested the home.

My guide explaining what conveyancing searches reveal places radon within the wider search package.

If the search shows an affected area, the buyer’s conveyancer should report the result and explain the available options. The conveyancer is not a radiation scientist or building specialist, but can deal with the contractual arrangements and any retention agreed with the seller.

The wider responsibilities are explained in my guide to what a conveyancing solicitor does.

What should you do when buying in a radon area?

Do not assume that an affected-area result means the house has an unsafe concentration. Begin by establishing what information already exists.

Ask whether the seller has carried out a validated three-month test. If so, obtain the complete report rather than relying on a verbal reassurance that the reading was “fine”.

Check:

  • when the test was carried out;
  • whether the home was occupied normally;
  • where the detectors were placed;
  • whether significant alterations have since been made;
  • whether the result exceeded 100 or 200 Bq/m³; and
  • whether any reduction measures were installed and retested.

If there is no suitable result, UKHSA recommends that a property in a Radon Affected Area should be measured.

A three-month test may be completed before exchange where both parties are willing to wait. In many transactions, that timetable is impractical. The buyer and seller can instead consider a contractual retention to fund testing and possible work after completion.

The buyer can also proceed without a retention and accept responsibility for testing and any eventual cost. That is a financial decision rather than proof that radon does not matter.

Before exchange, the buyer can ordinarily renegotiate or withdraw if the result or proposed arrangements are unacceptable. After exchange, the buyer is contractually committed unless the contract contains a relevant condition. My guide explains the significance of exchanging contracts.

What is a radon retention or radon bond?

A radon retention—sometimes called a radon bond—is an arrangement under which part of the sale money is held by one of the conveyancers after completion.

It allows the buyer to occupy the property normally and complete a three-month measurement without postponing the entire transaction.

UKHSA’s current house-sale guidance describes a typical retention of between £800 and £3,000. It says the money is commonly held for six months, allowing time for the buyer to move in, carry out the test, receive the result and arrange work where necessary.

The exact amount and wording are matters for agreement between the parties. A retention is not automatically imposed merely because a property is in an affected area.

The agreement should address:

  • the amount retained;
  • which conveyancer will hold it;
  • the deadline for placing and returning the detectors;
  • the form of test and acceptable laboratory;
  • what result triggers the use of the fund;
  • which reduction work is covered;
  • whether quotations or invoices are required;
  • the deadline for remedial work and retesting; and
  • when any unused balance will be released to the seller.

If the result is below the Action Level, the retained money will normally be released to the seller. If it exceeds the Action Level, the agreed fund can meet qualifying remedial costs, with any surplus returned to the seller.

A retention may be unsuitable where the buyer intends to leave the house empty or begin major building work immediately. Both situations can interfere with obtaining a representative measurement under normal occupation.

The official procedure is outlined in UKHSA’s guidance on radon and house sales.

What should a seller disclose about radon?

A seller is not generally required to commission a fresh radon test merely because the property lies in an affected area.

However, the seller must answer the Property Information Form carefully and honestly. Known test results, installed protective measures and remedial systems should not be concealed.

The buyer should be supplied with available reports, guarantees, invoices, operating instructions and subsequent retest results.

If the house contains an active fan, sump or ventilation system, the seller should explain where it is, whether it runs continuously and what maintenance has been carried out.

An inaccurate answer that induces the buyer to exchange contracts can potentially support a property misrepresentation claim.

A seller who does not know whether the property has been tested should say so rather than guess. The buyer can then decide whether to test before exchange or request a retention.

The current form and seller’s explanatory material can be found through the Law Society’s TA6 Property Information Form guidance.

How is a home tested for radon?

UKHSA recommends using a validated laboratory.

For an ordinary home, the measurement pack usually contains two small passive detectors. One is placed in a living area and the other in an occupied bedroom.

The detectors remain in position for approximately three months. They are then returned to the laboratory for analysis, and the result is adjusted to estimate the annual average concentration.

The detector does not emit radiation or collect dangerous material. It contains a small piece of plastic on which radon decay leaves microscopic tracks that can be analysed.

The test period is deliberately long because radon varies with weather, temperature, ventilation and occupancy. A three-month result is much more representative than a reading taken over a few days.

The property should be used normally during the measurement. Reliability can be reduced where:

  • the home is vacant for several weeks;
  • occupiers change during the test;
  • major building work is taking place;
  • the detectors are moved or incorrectly positioned; or
  • the measurement period is shortened.

You can obtain a test and see the current price through the official UKHSA home measurement service.

Can a short-term radon test be used?

Short-term and electronic monitoring products are available, but they require care.

Radon concentrations can change considerably from one day to the next. A result obtained during a short spell of unusually cold, warm, windy or still weather may not represent the annual average.

UKHSA therefore prefers measurements over approximately three months. It warns that shorter tests have greater uncertainty and are more likely to produce ambiguous or inconclusive results.

A short-term reading might alert an owner to a potentially high concentration or provide supplementary information. It should not automatically be treated as equivalent to a validated three-month measurement for a house-sale retention or final remedial decision.

If a buyer and seller intend to rely on a particular testing method contractually, the retention terms should identify it clearly.

What does a radon test result mean?

The report should provide an estimated annual average concentration for the property.

Below 100 Bq/m³

The result is below the UK Target Level. Radon will still be present, as it is in virtually every building, but reduction work will not normally be recommended on the basis of that result alone.

Between 100 and 200 Bq/m³

The result is below the Action Level but above the Target Level.

Reduction should be considered, particularly where an occupant is a smoker or former smoker or expects to remain in the property for a long period.

Relatively simple ventilation improvements may be appropriate, although the property and proposed method should be assessed properly.

At or above 200 Bq/m³

The result is at or above the Action Level. UKHSA recommends reducing the concentration as low as reasonably practicable, ideally below 100 Bq/m³.

A high result is not normally a reason to leave the building immediately. It is a reason to obtain suitable remedial advice and arrange work rather than accepting continuing long-term exposure.

The property should be measured again after the work to confirm that the chosen method has been effective.

How can radon levels be reduced?

The appropriate remedy depends on the measured concentration, floor construction, size and layout of the property.

Radon sump

An active radon sump creates a low-pressure area beneath a solid floor. A fan draws radon-containing air from beneath the building and discharges it safely outside before it enters the rooms.

UKHSA describes an active sump as the most effective general method for reducing radon in many homes with solid floors.

Underfloor ventilation

Where the house has suspended floors, improving ventilation beneath them can prevent radon-rich air accumulating and entering the living space.

The solution may involve clearing or adding airbricks or installing fan-assisted underfloor ventilation.

Positive house ventilation

A positive ventilation system introduces air into the home, creating pressure that can reduce the movement of radon from the ground into occupied rooms.

Its effectiveness depends on the building and initial radon level. It is not the right solution for every property.

Sealing entry points

Cracks, service penetrations and gaps may be sealed as part of a wider programme.

Sealing alone is often difficult to rely upon because entry routes may be numerous or inaccessible. It is more commonly used alongside ventilation or a sump.

The system must also be installed without creating other safety problems. For example, changes in airflow can affect combustion appliances, moisture and indoor air quality. Specialist advice is sensible before installing fans or altering underfloor ventilation.

UKHSA outlines the main options in its guidance on reducing radon levels in homes.

How much does radon reduction cost?

The cost depends on the property and method required.

UKHSA’s house-sale guidance currently uses approximately £1,000 as a typical remediation cost when explaining retentions. That should be treated as a broad illustration rather than a quotation for every house.

A straightforward ventilation measure may cost less. A more complicated sump, extensive pipework, electrical installation or combination of measures may cost substantially more.

The initial work is not always the end of the expense. Fan-assisted systems use electricity and may require maintenance or eventual replacement.

Where the buyer and seller are agreeing a retention, the amount should reflect the property, measured or estimated risk, proposed method and likely cost rather than automatically adopting a standard figure.

A buyer should also establish whether the remedial contractor’s price includes the recommended three-month retest.

Do new-build homes need radon testing?

Building Regulations and associated guidance require radon-protective measures in new buildings and certain extensions within relevant risk areas.

Depending on the probability band, the construction may require basic or full protection.

Basic protection normally involves a radon-resistant barrier across the ground floor.

Full protection combines the barrier with provision for additional reduction, such as a standby sump or ventilated underfloor void.

A standby sump is not necessarily operating when the home is built. It may be capped and available for a fan or vent pipe to be added if later testing shows that the barrier alone has not reduced the concentration sufficiently.

Protective construction reduces risk but does not guarantee that the finished home will remain below the Action Level. UKHSA recommends a three-month measurement within the first year of occupying a new home in an affected area.

Ask the developer for:

  • confirmation of the radon-risk category;
  • details of the protective measures installed;
  • drawings showing any membrane and standby sump;
  • completion and building-control documents; and
  • instructions for activating or maintaining the system.

The official position is explained in the guidance on radon and Building Regulations.

Does radon affect mortgages, insurance or value?

Being in a Radon Affected Area does not, by itself, prove that a house has an elevated reading or make it automatically unsuitable for a mortgage.

The buyer’s conveyancer must nevertheless report and deal with the search result in accordance with the lender’s instructions. The lender may expect the buyer to test, accept advice or enter into a suitable retention arrangement.

A known high result that has not been investigated may create more concern than an affected-area classification alone. A satisfactory remedial installation followed by a validated low retest provides much clearer evidence for future buyers and lenders.

Home insurance policies vary. A buyer should not assume that an ordinary buildings policy will pay for preventive radon work or an existing elevated reading. The insurer or policy wording should be checked where cover matters to the decision.

There is no standard percentage by which radon reduces a property’s value. The practical effect depends on:

  • the probability band;
  • whether the property has been tested;
  • the actual result;
  • the cost and appearance of remedial work;
  • whether a system has been maintained and retested; and
  • how common radon-affected properties are in the local market.

In a locality where many homes are within affected areas, buyers and conveyancers may regard testing and reduction as familiar parts of the transaction.

What are a landlord’s responsibilities?

Radon is included within the radiation hazard considered under the Housing Health and Safety Rating System in England.

For a rented property in a Radon Affected Area, the potential hazard should be assessed. Where testing shows an unsafe concentration, the landlord may need to take appropriate steps to reduce the risk.

Local authorities use the HHSRS to assess residential hazards and must take action where they identify a category 1 hazard. They have powers to deal with category 2 hazards.

The Government’s current guidance explains the Housing Health and Safety Rating System for landlords and agents.

Wales has its own fitness-for-human-habitation framework. Welsh Government guidance states that radon levels in domestic properties should be reduced where the average exceeds the Action Level.

A tenant concerned that their home is in an affected area should ask the landlord about previous testing. If the issue is not addressed, the local authority’s environmental health or private-sector housing team may be able to advise.

When should a property be retested?

There is no single statutory domestic retesting interval applying to every home.

A further three-month measurement is important after remedial work. Without it, the owner does not know whether the system has actually reduced the annual average sufficiently.

Retesting should also be considered after significant changes that may alter airflow or contact with the ground, including:

  • an extension or conservatory;
  • basement conversion;
  • new floors or major structural work;
  • replacement windows and substantial draughtproofing;
  • changes to heating or ventilation; and
  • alterations to an existing radon-reduction system.

Fan-assisted systems can stop working or become less effective. Their operation should be checked and the manufacturer’s maintenance instructions followed.

Guidance associated with some radon-reduction systems recommends repeat measurements at intervals of approximately five to ten years and after a change of occupier or substantial building work.

A new owner should be cautious about relying indefinitely on a decades-old result where the property or its use has changed.

Should you buy a house in a radon area?

In most cases, the answer can still be yes.

A Radon Affected Area covers probabilities ranging from relatively modest to high. Even within the highest bands, the search does not establish the concentration in the particular house.

The sensible response is evidence rather than panic:

  1. Obtain the address-level risk report.
  2. Ask for previous test and remediation records.
  3. Arrange a validated three-month measurement where practical.
  4. Consider a properly drafted retention if testing must follow completion.
  5. Obtain suitable remedial advice if the result reaches the Action Level.
  6. Retest after the work.

I would be more concerned by a seller who concealed a known high result or could not explain an active system than by the simple fact that a home stands in a familiar radon area.

Radon is a genuine health risk, but it is also a measurable and usually manageable feature of a property. A buyer who understands the result and has a clear plan is in a much stronger position than one who either panics at the word or ignores it altogether.

Frequently asked questions

Read more

Measure the house, not the postcode

The words “Radon Affected Area” can make a property search sound far more conclusive than it is.

The search tells you that the geology and existing evidence justify further attention. It does not tell you what concentration exists in the living room or bedroom of the home you are buying.

That requires a properly conducted measurement. If the result is high, the response is not guesswork or panic but appropriate building work followed by another test.

Radon should be taken seriously because the health evidence is clear. It should also be kept in proportion because most homes have low levels and effective reduction methods are well established.

The most useful question is therefore not simply, “Is this house in a radon area?”

It is: “What is the measured level, and what practical arrangement is in place if it needs to be reduced?”

Last legally reviewed: 2 August 2026

This guide is based on general principles of English and Welsh law, is intended for informational purposes only, and does not constitute legal advice or establish a professional relationship.

About the author, Clare Lowes

Hello,

I’m Clare, the Silver Brief

Clare Lowes, creator of The Silver Brief

After almost 25 years practising law in England, I retired in 2025. Now a non-practising solicitor, I created this blog to share clear, jargon-free, and objective legal insights. I hope you find the content helpful.

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