Radon Gas in Property — Checking Risk and Reducing Exposure

What is Radon?

Radon is a naturally occurring, colourless, odourless, radioactive gas formed by the decay of uranium in rocks and soils — particularly granite and certain sedimentary formations. It seeps up from the ground and into buildings through foundations, floors, and walls.

Once inside a poorly ventilated building, radon can accumulate to concentrations that pose a significant health risk.

Why Radon Matters for Property Owners

Radon is the **second leading cause of lung cancer in the UK** after smoking, responsible for approximately 1,100 deaths per year according to the UK Health Security Agency (UKHSA). The risk increases substantially at higher concentrations and with longer periods of exposure.

For property owners and buyers, radon is a material consideration that is largely invisible without testing — and is not always disclosed by sellers.

Which Areas Are Affected?

Radon levels vary significantly by local geology. The highest-risk areas in England include:

• **South West England** — Devon, Cornwall, and Somerset have the highest concentrations due to underlying granite geology
• **Derbyshire** and parts of the Peak District
• **Northamptonshire** and parts of the East Midlands

In Wales, areas of Powys, Gwynedd, and Ceredigion have elevated risk. Scotland has affected areas in Aberdeen, Angus, and the Highlands.

The UKHSA publishes a **radon potential map** at ukradon.org, which allows any UK address to be checked for estimated radon potential. A radon potential of 1–10% means 1–10% of homes in that area are likely to exceed the action level.

How to Test Your Home

The only way to know the actual radon level in a property is to test it. The standard test uses two small detectors placed in the main living area and a bedroom for **three months** (to account for seasonal variation).

Test kits are available from Public Health England and UKHSA-accredited laboratories, typically costing **£40–£60** for two detectors, return postage, and laboratory analysis. Results are reported in becquerels per cubic metre (Bq/m³).

Understanding the Results

The UK action level is **300 Bq/m³**. The target level after mitigation is below **100 Bq/m³**.

Mitigation Measures

If testing reveals levels above the action level, several measures can reduce indoor radon concentrations:

• **Positive input ventilation (PIV):** a fan unit installed in the loft draws fresh air into the property, diluting and displacing radon. Cost: approximately £400–£700 installed.
• **Radon sump (sub-slab depressurisation):** a pipe is installed through the floor slab, connected to a fan that draws radon from beneath the floor before it enters the building. This is the most effective method for high concentrations. Cost: approximately £1,000–£2,500.
• **Improved underfloor ventilation:** for properties with suspended timber floors, increasing airbricks and ventilation beneath the floor reduces accumulation. Cost: £200–£800.
• **Sealing floors and walls:** reducing entry points through cracks and gaps. Less effective as a standalone measure but useful in combination.

Buying in an Affected Area

If you are buying in a radon-affected area:

1. Check the UKHSA radon potential map before commissioning a survey

2. Ask the seller for any historical radon test results

3. The **environmental search** (ordered by your solicitor) will flag whether the property is in a radon-affected area

4. Factor the potential cost of testing and mitigation into your offer if the property is in a higher-risk area

A radon test takes three months to complete — you are unlikely to have results before exchange. Budget for testing post-completion in affected areas, and include a mitigation allowance in your purchase calculations.

Property Passport UK records property data including environmental risk indicators for registered properties, helping owners understand and document material factors for future buyers.