Buyer Guides
Radon gas risk when buying a house: what buyers need to know
Radon is a naturally occurring radioactive gas produced by the decay of uranium in some UK rocks and soils. Above the UKHSA Action Level of 200 Bq/m³, radon is a recognised long-term lung cancer risk. The conveyancer's environmental search flags whether the property sits in a designated radon-affected area; a 3-month test gives the reading at the address.
Last updated: 6 May 2026. Editorially reviewed: 20 May 2026.
Tool shortcut
Check the property before you offer
Flood, subsidence, EPC, crime, schools, transport, broadband, tenure, age, listed status and price checks where data is available.
Run a free previewWhat radon is and where it occurs
Radon is colourless, odourless and chemically inert. It enters buildings through cracks in floors, gaps around services, and basement walls. The UK Health Security Agency (UKHSA, formerly Public Health England) maps radon-affected areas based on geological risk, uranium-bearing granite, certain limestones and Old Red Sandstone are the typical sources.
The highest-risk regions in the UK are the South West (Cornwall, Devon, parts of Somerset), the Pennines, parts of Northamptonshire and Cumbria, and pockets across Scotland and Wales. Within affected areas, individual property risk varies based on construction, ventilation and ground contact.
How to test for radon
The standard UK test is a 3-month etched-track detector kit from UKRadon (a UKHSA service). Two detectors are placed in occupied rooms and returned for analysis. The result is the average concentration over the test period. Short-term tests are not reliable for property decisions.
Test cost is typically £40–£60 from UKRadon, plus return postage. Results take 2–4 weeks after the 3-month exposure period. For a buyer mid-purchase, this timing rarely fits the conveyancing window, most buyers proceed on the basis of the conveyancer's environmental search and any test the seller has already done, with mitigation budgeted as an after-purchase action if results show high readings.
Radon mitigation: what works and what it costs
Above the Action Level, mitigation is recommended. The standard solutions for existing properties:
- Radon sump and fan: a small pump installed beneath or alongside the floor slab pulls radon-laden air out from under the building before it can enter. Typically £1,000–£3,500 supply and fit.
- Active ventilation upgrade: improved sub-floor ventilation, increased airbrick provision, sometimes a positive-input ventilation system. £500–£2,000.
- Radon membrane retrofit: more disruptive, a sealed barrier added to the floor slab during major works. £3,000–£8,000.
- New-build radon barrier: a sealed membrane below the slab, included in build cost in affected areas under Building Regulations Part C.
What radon means for your mortgage and insurance
Mortgage lenders rarely refuse on radon alone. Where the conveyancer's environmental search flags a designated radon-affected area, lenders may want documented mitigation or an undertaking to test and remediate post-completion. Specialist lenders may apply additional conditions.
Insurance is not directly affected. Radon is a long-term health risk, not a property-damage one. The buyer's medical and family-planning consideration is more important than the property-financial one.
What to ask the seller
- Has a radon test been carried out, and what was the reading?
- Is any mitigation system installed, and is documentation available?
- Is the property in a designated radon-affected area according to UKHSA mapping?
Related decoder findings
Run the check on this address
A free preview pulls flood, subsidence, EPC, building age and listed status for any UK address in 15 seconds. The full report adds the remaining 7 checks.
Run the check
Check the property before you offer
Flood, subsidence, EPC, crime, schools, transport, broadband, tenure, age, listed status and price checks where data is available.
Run a free previewFrequently asked questions
Is radon a reason to pull out of a house purchase?
Almost never on its own. Radon is treatable with relatively modest mitigation works (£1,000–£3,500 typically). Pull out only if mitigation cost is unviable. The seller refuses to engage, and the buyer's medical situation makes long-term exposure a personal concern.
How accurate is the conveyancer's radon search?
It tells you whether the property is in a designated radon-affected area based on geology, not what the actual reading is in this specific home. For the actual reading, a 3-month UKRadon test is needed.
Do new builds have radon barriers?
In designated radon-affected areas, Building Regulations Part C requires a radon barrier under the slab. New builds outside designated areas do not require this but some developers include it as standard.
Should I test for radon before exchange?
If time allows. Most buyers do not. A 3-month test rarely fits the conveyancing window, and mitigation is straightforward enough to handle post-completion. The exception is high-risk areas (e.g. parts of Cornwall) where test results can shift offer terms.
Editorial review
Editorial owner: BiteRight Ltd, operator of MyPropertyScan. We review buyer guides against UK public property datasets, RICS survey wording, lender requirements, and common buyer questions.
Pages are updated when source coverage, property-risk guidance, survey cost assumptions, or product checks materially change. Methodology and dataset limitations are explained on the MyPropertyScan methodology page.
Sources used
We use UK public and specialist sources where they are available. Public datasets can be incomplete, delayed, or missing for some addresses. Treat them as a starting point, not as a replacement for professional advice.
Source standard: preference goes to official government datasets, statutory bodies, professional standards, and primary dataset publishers. We cite the source family on the page and explain coverage limits rather than filling gaps with unsupported estimates.
General information only. Not legal, mortgage, insurance, or surveying advice. Always confirm with your own surveyor, broker, and conveyancer before making decisions. MyPropertyScan is operated by BiteRight Ltd.