Radon is colourless, odourless, and invisible — the only way to detect it is with a dedicated measurement device. It enters buildings through gaps in floors, walls, and service penetrations from the underlying geology. Levels vary enormously by location and building type: most of England has very low radon levels, but certain areas — particularly parts of Cornwall, Devon, Somerset, Derbyshire, Northamptonshire, Lincolnshire, and parts of Scotland and Wales — have significantly elevated average radon concentrations.
Landlords are increasingly encountering radon as a compliance issue through two routes: the HHSRS (which lists radon as a Category 1 or Category 2 hazard depending on measured levels), and the Material Information obligations introduced in 2023-24 requiring agents and landlords to disclose known radon risk at the marketing stage. Proactive testing, particularly in high-radon areas, protects both tenants and landlords.
Radon-affected areas in England — how to check
Radon risk is geologically determined. High-risk areas in England include:
- Cornwall and Devon: The highest-risk area in England. Granite geology produces high uranium concentrations. Large areas of Cornwall have greater than 10% of properties above the action level
- Somerset and the Mendip Hills: Limestone and granite geology in parts of Somerset, including around Shepton Mallet, Frome, and the Mendips
- Derbyshire and the Peak District: Parts of the Peak District and surrounding areas, particularly around limestone outcrops
- Northamptonshire, Rutland, and Lincolnshire: Iron ore and limestone geology in parts of these counties produce elevated radon levels
- Parts of the Cotswolds: Certain Cotswold areas with oolitic limestone
- Check the UKHSA interactive map: The UK Health Security Agency (UKHSA, formerly Public Health England) provides an online postcode-level radon risk indicator at ukhsa.gov.uk. This shows the percentage of properties in each 1km grid square estimated to be above the action level — a grid with 1–3% above the action level is 'lower risk', 3–10% is 'higher risk', and 10%+ is 'highest risk'
- Being in a lower-risk area does not guarantee the property is below the action level — local geology, construction type, and building condition all affect the actual measured concentration. The only way to know is to test
The UKHSA action level and HHSRS implications
There are two key thresholds for radon in homes:
- 200 Bq/m³ — the action level: Above this level, the UKHSA recommends remediation action to reduce radon levels. This is the level at which the HHSRS will treat radon as a Category 1 hazard (the highest category, triggering a duty on the local authority to take action if it inspects the property). A Category 1 HHSRS hazard can result in an Improvement Notice requiring the landlord to remediate
- 100 Bq/m³ — the target level: UKHSA recommends remediation measures for properties above this level, even if they are below the 200 Bq/m³ action level. If you discover your property is between 100–200 Bq/m³, you should still take steps to reduce levels
- Below 100 Bq/m³: no action required from a regulatory standpoint
- The HHSRS framework means that a local authority can serve an Improvement Notice on a landlord where radon levels above the action level are identified — either proactively through a landlord test or following a tenant complaint
- Failure to comply with an HHSRS Improvement Notice is a criminal offence under the Housing Act 2004 with a fine up to £5,000 on conviction in the magistrates' court
How to test for radon
Radon levels fluctuate seasonally — levels tend to be higher in winter (when windows are closed and heating is on) than in summer. UKHSA recommends a minimum 3-month measurement period to get a representative annual average:
- Passive alpha-track detectors (charcoal canisters / CR-39 etched-track detectors): The most common and cost-effective method. Two small detector devices are placed in the property (one in the main habitable room, one in the bedroom) for 3 months, then sent to a laboratory for analysis. Cost: approximately £50–£80 per test including laboratory analysis
- Electret ion chamber detectors: An alternative measurement device, less common for residential use
- UKHSA-approved laboratories: Test kits should be obtained from, and analysed by, a laboratory accredited by the UKHSA Radon Survey Programme. Approved suppliers include Radonova, Scientific Measurements Ltd, and Radonseal. Do not use non-approved suppliers — the results will not be accepted for regulatory or insurance purposes
- Short-term tests: Faster 'grab sampling' or electronic monitors can give an indicative reading, but these are not accepted as a definitive measurement for HHSRS or regulatory purposes. A 3-month passive measurement is the accepted standard
- Test in the ground floor and first floor. In a basement flat or semi-basement, test in the lowest occupied space — these areas typically have the highest concentrations
Radon remediation options
Where radon levels exceed the action level (200 Bq/m³), several remediation approaches can reduce concentrations significantly:
- Positive pressure unit (PPU): A fan-driven unit that pressurises the living space, preventing radon entry from below. Relatively low cost (£400–£600 supply and install) and effective in many property types. Does not require access below the floor. Works by dilution and pressure differential
- Sump system (sub-floor depressurisation): A small pipe and fan system draws radon from beneath the floor slab and exhausts it outside before it can enter the building. Highly effective — typically reduces radon by 80–90%. Cost: £800–£1,500. Most effective under solid concrete ground floors
- Sub-floor ventilation (suspended timber floors): Installing air bricks or powered sub-floor ventilation to increase airflow beneath a suspended timber ground floor. May reduce levels by 50–75%. Cost: £200–£600
- Sealing cracks and service penetrations: Sealing gaps around pipework, floor/wall junctions, and cracks in solid floors can reduce entry pathways. Effective as a complementary measure but rarely sufficient on its own for high-level properties
- After any remediation, re-test after 3 months (winter if possible) to confirm the reduction. If levels remain above the action level, a more powerful or different approach is needed
- UKHSA maintains a list of radon remediation contractors who have demonstrated competence and signed up to a code of practice
Disclosure requirements for landlords and agents
Radon risk must be disclosed under Material Information rules:
- National Trading Standards (NTS) Material Information Part B (published 2023) requires lettings agents and landlords marketing a property to disclose whether the property is in a radon-affected area. This is property-specific material information that must be included in the property listing where it applies
- Non-disclosure of known radon risk to a prospective tenant is likely to constitute a breach of the Consumer Protection from Unfair Trading Regulations 2008 and may be actionable
- If you have tested the property and found levels above the action level, full disclosure — and remediation before re-letting — is strongly recommended
- Some landlord insurance policies now ask whether properties have been tested for radon; failure to disclose known elevated radon risk could invalidate a claim
Frequently asked questions
Do I have to test for radon even if I am not in a high-radon area?+
There is no legal obligation to test in lower-risk areas, but it is prudent to test if your property has a ground floor or basement in any area with elevated geological risk. The Material Information rules require disclosure if the property is in a radon-affected area — the UKHSA map is the reference point. If the map shows 1% or more of properties in your grid square may be above the action level, disclosure is advisable. Testing is cheap (£50–£80) and provides a definitive answer.
My tenant is complaining about radon — what should I do?+
Take the complaint seriously. Commission a 3-month UKHSA-approved radon test immediately (preferably in winter). If the result is below 100 Bq/m³, no action is required but communicate the result to the tenant. If the result is 100–200 Bq/m³, consider remediation and inform the tenant. If the result is above 200 Bq/m³, take remediation action promptly — this is a Category 1 HHSRS hazard and the local authority has a duty to act if it receives a complaint. Failure to remediate above the action level could result in an HHSRS Improvement Notice and potential criminal prosecution.
Can I sell a property with elevated radon levels?+
Yes, but you must disclose the known radon levels under the Material Information rules. Failure to disclose known elevated radon risk to a buyer is likely actionable misrepresentation. Where levels have been tested and remediation has been carried out successfully, disclose both the original level and the post-remediation measurement. Some buyers will want independent post-sale testing before exchanging. Remediated properties with documented low levels are significantly easier to sell than untested or unmitigated ones.
Is radon a problem for upstairs flats?+
Generally less so. Radon concentrations decrease with height above the ground floor — it enters through the floor and disperses as it rises through a building. Ground floor and basement flats are at the highest risk. Upper floor flats in a block are typically at much lower concentrations. However, in a ground floor flat or house with a concrete slab ground floor in a high-radon area, levels can be very significant even on the first floor if the building has poor sealing around service penetrations.