Radon is a naturally occurring radioactive gas that can enter buildings through cracks, gaps, and other openings in contact with the ground. It is colourless, odourless, and impossible to detect without specialist radon testing.
While radon is present in homes throughout the UK, concentrations vary significantly depending on local geology, property construction, and ventilation. It is estimated to contribute to more than 1,100 lung cancer deaths in the UK each year, making it the second leading cause of lung cancer after smoking.
Some parts of the country have a much higher likelihood of elevated radon levels than others. Understanding whether you live in one of these affected areas is an important first step in assessing your risk.
Why Some Areas Have Higher Radon Levels
Radon is produced naturally when uranium present in rocks and soils breaks down over time. Areas with large deposits of granite, limestone, and certain other rock types tend to generate higher levels of radon gas.
Once released from the ground, radon can travel through soil and enter buildings through cracks in foundations, service penetrations, suspended floors, and other small openings.
However, geology is only part of the picture. Two neighbouring properties can have very different radon levels depending on factors such as construction methods and whether the property includes a basement or cellar. This is why mapping data should always be treated as a guide rather than a guarantee.
Which Parts of the UK Are Most at Risk?
While radon can be found anywhere in the UK, certain regions have a much greater likelihood of elevated levels due to the geology beneath them. Areas with granite, limestone, and other uranium-bearing rocks are generally more susceptible, as these materials naturally release radon as they break down over time.
Cornwall and Devon
Cornwall and Devon are widely recognised as having some of the highest radon potential in England. The region sits on the Cornubian Batholith, a large granite formation that extends beneath much of the South West. As a result, parts of Cornwall and Devon contain areas where more than 30% of properties are estimated to exceed the UK Action Level of 200 Bq/m³.
However, radon risk varies considerably across the region, and even neighbouring properties can record very different readings.
Somerset and Gloucestershire
Parts of Somerset and Gloucestershire are also associated with increased radon potential, particularly around the Mendip Hills and sections of the Cotswolds. These areas are underlain by limestone formations that can contain naturally occurring uranium, creating conditions that allow radon to be released into the surrounding ground.
Derbyshire and the Peak District
The Peak District is one of the UK's best-known radon-affected regions. Much of the area is underlain by Carboniferous limestone and other mineral-rich geological formations that can generate elevated radon levels. Parts of Derbyshire consistently appear within recognised radon-affected areas identified by UKHSA and the British Geological Survey.
Northamptonshire
Northamptonshire is often overlooked when discussing radon risk, yet parts of the county have historically shown elevated radon potential. This is largely due to the county's Jurassic ironstone and limestone geology, which contains naturally occurring radioactive elements that can contribute to radon generation.
Yorkshire, Northumberland, and Cumbria
Several areas across northern England, including parts of the Yorkshire Dales, Northumberland and Cumbria, are associated with higher radon potential. The combination of limestone bedrock, historic mineralisation and local geological variations can increase the likelihood of elevated radon levels in some properties. The Yorkshire Dales and Lake District are particularly notable examples.
Wales
Wales contains some of the most significant radon-affected areas in the UK. Elevated risks are found across parts of North and West Wales, including areas of Pembrokeshire and Anglesey. The combination of granite, slate, and other uranium-bearing geological formations contributes to the higher concentrations recorded in these regions.
Scotland
Parts of Scotland, particularly regions underlain by granite bedrock, also experience increased radon potential. Areas around the Grampian Mountains and Aberdeenshire are among the best-known examples, with the local geology creating favourable conditions for radon generation and migration into buildings.
How to Check Your Area Using the UKHSA Radon Map
If you're concerned your property may be located in a radon-affected area, the UK Health Security Agency (UKHSA) provides a free online map that allows you to assess the estimated radon risk for your postcode.
- Visit the UK government's radon map
- Enter your postcode and select 'Show Radon Data'
- Review the colour-coded results for your location
The map estimates the percentage of properties within each area that are likely to exceed the UK Action Level of 200 Bq/m³. The lightest areas indicate a very low probability of elevated radon levels, while the darkest areas represent locations where more than 30% of properties are expected to exceed the Action Level.
Why the Map Alone Isn’t Enough
While the UKHSA map is an excellent starting point, it's important to understand its limitations.
The map does not provide a reading for your individual property. Instead, it shows the probability of elevated radon levels across geographic areas measuring approximately 1 km². This means two neighbouring properties - or even two houses on the same street - can have very different radon concentrations.
A property's radon level can be influenced by a range of factors, including:
- Building construction and foundation type
- The presence of basements or cellars
- Ventilation levels
- Local ground conditions and soil permeability
- Seasonal changes throughout the year
As a result, properties in areas shown as low risk can still exceed the UK Action Level, while some homes in higher-risk areas may have relatively low readings.
It's also worth noting that the map provides a broad overview of risk and cannot account for changes made to individual properties since the data was compiled.
Why Radon Is Worse in Winter
One of the biggest influences on indoor radon levels is the time of year. In many properties, radon concentrations are significantly higher during the winter months than they are during the summer.
There are two main reasons for this:
Stack Effect
The stack effect is the natural movement of air through a building. During winter, warm indoor air rises and escapes through small gaps and openings in the roof and upper parts of the property. As this air leaves, it creates a slight negative pressure inside the building, which can draw radon-containing soil gas up from the ground and into the property through cracks, gaps and service penetrations.
At the same time, doors and windows are typically kept closed during colder weather, reducing natural ventilation and allowing radon to accumulate indoors.
Sealed Homes
Modern homes and renovated properties are often designed to be more energy efficient, with improved insulation, draught-proofing and air-tightness measures. While these improvements help reduce heat loss, they can also reduce natural air exchange, making it easier for radon to build up if it enters the property.
Why This Matters
Because radon levels can vary significantly throughout the year, a test carried out during the summer may not fully reflect the higher concentrations that can occur during colder months.
To gain the most accurate understanding of your radon exposure, we typically recommend:
- Starting a three-month passive test during autumn, allowing the monitoring period to capture winter conditions while still reflecting longer-term exposure.
- Using real-time monitoring where appropriate, helping to identify seasonal changes, daily fluctuations and periods of elevated radon levels.
Together, these approaches can provide a more complete picture of how radon behaves within a property and help inform any mitigation decisions that may be required.
Why a "Safe" Average Can Still Mean Dangerous Peaks
The main advantage of passive testing is that it provides an average radon reading over a three-month period, helping to build a picture of long-term exposure.
However, averages do not always tell the full story. Radon levels can fluctuate significantly throughout the day and across different seasons. For example, concentrations often increase overnight when doors and windows are closed, or during colder weather when the stack effect is stronger. As a result, a property with an average reading of 160 Bq/m³ could still experience occasional peaks of 350-400+ Bq/m³.
This is where real-time monitoring can be particularly valuable. By measuring radon levels continuously, it allows professionals to identify fluctuations, track exposure patterns and detect any significant spikes that may be hidden within an average result.
Who Should Test Regardless of Their Postcode
While radon risk maps provide a useful indication of local risk, they cannot predict the radon concentration in an individual property. Even if you live in an area considered low-risk, testing is still recommended in the following circumstances:
Basement & Cellar Owners
Basements and cellars are in direct contact with the ground, making them particularly vulnerable to radon ingress. Because these spaces often have more potential entry points and lower levels of natural ventilation, they can experience significantly higher radon concentrations than upper floors.
New-Build Buyers
Many new homes in radon-affected areas are constructed with protective measures such as radon barriers or membranes. However, no system is guaranteed to perform perfectly, and damage during construction or installation defects can reduce effectiveness. Testing is the only way to confirm that these measures are working as intended.
Property Buyers & Sellers
Radon levels can influence both property value and a buyer's confidence in the transaction. Testing provides reassurance and allows any issues to be identified before completion. Where timescales are limited, such as during a property sale, real-time monitoring can provide faster insights than a traditional three-month passive test.
Smokers & Ex-Smokers
The health risks associated with radon are significantly higher for people who smoke or have smoked in the past. Radon and tobacco smoke have a combined effect on lung cancer risk, making testing particularly important for current and former smokers, regardless of postcode.
Employers With Ground-Floor or Basement Workplaces
Employers have a legal duty to protect the health and safety of employees and visitors. Workplaces located at ground level, below ground level, or in areas with known radon potential may require a radon assessment under relevant health and safety legislation. Testing helps employers identify any risks and take appropriate action where necessary.
Passive vs Real-Time Testing: What's the Difference?
Passive testing is the industry-standard method for measuring long-term radon exposure. It uses detectors placed within a property for an extended period - typically around three months - to provide an average radon reading over time. This lower-cost approach helps account for seasonal fluctuations and is the method recommended by the UKHSA for assessing overall radon risk.
Real-time testing uses electronic monitoring equipment to measure radon levels continuously over a much shorter period, often within 48 to 72 hours. While generally more expensive, it provides detailed insight into how radon levels fluctuate throughout the day, helping to identify peak exposure periods, patterns, and even potential sources of radon ingress.
The right option depends on your objectives. Passive testing is ideal for establishing long-term exposure, while real-time testing can provide faster answers and a more detailed understanding of how radon behaves within a property.
See the comparison table below:
| Passive Testing | Real-Time Testing | |
|---|---|---|
| Results timeline | 3-4 months | 48-72 hours |
| Data shown | Long-term average only | Full fluctuation range |
| Can be manipulated | Possible | No, surveyor controls test |
| Suitable for conveyancing | No | Yes |
| Mitigation recommendations included | No | Yes |
| Cost | Lower | Higher |
What to Do If Your Levels Are High
Receiving a high radon result can understandably be concerning. However, the good news is that elevated radon levels can usually be reduced significantly with the right mitigation measures.
The UK Health Security Agency recommends taking action if radon levels exceed 200 Bq/m³, known as the UK Action Level. If your readings fall between 100-200 Bq/m³, known as the Target Level range, mitigation should still be strongly considered, particularly if the property is occupied for long periods or by vulnerable individuals.
The most important next step is understanding how radon is entering your property and selecting a mitigation strategy that addresses the source of the problem. With the correct approach, radon levels can often be reduced well below recommended limits, helping to protect both your health and the long-term value of your property.
What Mitigation Strategies Can I Take?
There is no one-size-fits-all solution for radon mitigation. The most effective approach depends on factors such as the property's construction, radon concentration, ventilation levels and how radon is entering the building.
Positive Input Ventilation (PIV)
Positive Input Ventilation (PIV) is a whole-house ventilation solution commonly used to help reduce indoor radon concentrations.
The system introduces a continuous supply of filtered fresh air into the property, creating a gentle positive pressure that helps dilute and displace radon-laden air. As well as helping to manage radon, PIV systems can also improve overall indoor air quality and reduce condensation-related issues.
At Better Indoors, we specialise in the design and installation of PIV systems and have installed more than 10,000 ventilation systems across the UK.
Radon Sump Extraction System
A radon sump is designed to intercept radon gas before it enters the building. Installed beneath or adjacent to a property, the system draws radon from the ground and safely vents it outside, preventing it from accumulating indoors.
Radon sumps are particularly effective where ground conditions and property construction make them suitable. In some cases, they may be used alongside other mitigation measures to achieve the best possible reduction in radon levels.
Our Recommended Approach
The most effective radon mitigation strategy is always based on the results of testing and a thorough assessment of the property.
In many cases, a combination of ventilation improvements and source-control measures can provide the greatest reduction in radon concentrations. By tailoring the solution to the building, it is possible to achieve long-term, reliable protection rather than relying on a generic approach.
How Better Indoors Can Help
Concerned about radon in your home? At Better Indoors, we offer professional testing, with real-time results in 48 to 72 hours, and expert mitigation design for any UK property.
Working UK-wide, we are a trusted and accredited national leader in improving the health of UK homes.
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