Will insulating or draught-proofing raise radon levels?

The short answer

Yes, it can. Insulation, new windows and draught-proofing reduce the amount of outdoor air leaking into a home, and that air is part of what dilutes radon seeping up from the ground. It matters most in homes that already have raised radon.

That is not a reason to skip insulation. It is a reason to know your radon level, keep the home ventilated, and test again after major energy work if you live in an area where radon is more likely.

Why does airtightness affect radon?

Radon is a natural radioactive gas from uranium in rocks and soil. UKHSA explains on its UKradon website that buildings naturally draw air in from the ground through cracks and gaps in their floors, and that this air contains radon. Its page on the health risks of radon says radon causes over 1,100 lung cancer deaths a year in the UK.

In a draughty house, a lot of outdoor air comes in through gaps around windows, doors and floors and mixes with the radon. Seal those gaps and less fresh air arrives, so radon that enters from the ground is less diluted.

What does the evidence show?

A study of 470,689 UK homes, published in the journal Indoor Air in 2019, compared radon measurements with records of energy efficiency work. On average, homes with double glazing measured 67% higher than homes with no recorded insulation or glazing work, homes with loft insulation 47% higher and homes with wall insulation 32% higher.

Those are averages across many homes. The study shows an association, not a prediction for any particular house. The figures matter most for homes in radon Affected Areas, where a rise could take a home over the level at which UKHSA recommends action.

Which homes should check before or after energy work?

Start with the property's radon potential. UKHSA's official radon maps show where raised indoor radon is more likely, and our guide to what a radon map can tell you explains how to read them. If the home is in an Affected Area and has never been tested, test it, whether or not you're planning energy work.

If you already have a result, keep it. A test before major work gives you a baseline; a test after the home is lived in normally again shows whether anything changed. UKHSA notes that results are less reliable if building work is going on during the test, so wait until the work is finished.

How is radon measured?

UKHSA's standard home test runs for three months with two detectors, one in a living area and one in a bedroom, so that it reflects the annual average rather than one moment. UKHSA recommends reducing radon in homes where the annual average is above the Action Level of 200 Bq/m³, and says the Target Level of 100 Bq/m³ is the ideal outcome. See how radon testing works for the practical steps.

How do I insulate without trapping radon or damp?

The government's guidance on damp and mould in the home warns that some energy efficiency work may reduce overall ventilation rates, and says it is essential to consider, with professional advice, whether ventilation needs improving at the same time. If it isn't addressed, the guidance says, the risk of damp and mould and poor indoor air quality can rise.

The Energy Saving Trust's draught-proofing advice says not to block vents, chimneys or airflow needed for safety, not to seal gaps into kitchens, bathrooms, utility rooms or rooms with open fires and flues, and to leave trickle vents open. It adds that a home with no trickle vents, wall vents or mechanical ventilation may already be too airtight for draught-proofing. This guide to draught-proofing and weather sealing covers the practical side.

Keep air bricks clear too. Under suspended timber floors they ventilate the void below, which UKHSA lists as one way to lower radon in homes with that kind of floor.

Will ventilation alone keep radon down?

Not reliably. UKHSA's guidance on reducing radon levels says sealing floors and adding extra ventilation do not reduce radon on their own. Where a test shows radon above the Action Level, UKHSA describes an active radon sump, a small pipe and fan drawing gas from under the floor, as the most effective method. Read about professional radon mitigation and how a radon sump works.

What about insulation grants?

Radon testing is a separate step from applying for energy efficiency funding, and one doesn't hold up the other. Grant schemes change often, so check what is open now: this overview of current home energy grants and who can apply is a good place to start. If you live in an Affected Area, plan a radon test into the project.

Common questions

Should I avoid double glazing in a radon area?

No. Fit it, use the trickle vents, and test the home once it's lived in normally if you haven't already.

Does draught-proofing a suspended floor raise radon?

It can reduce the air reaching the room above. Seal gaps in the floor surface if you like, but keep the air bricks outside clear so the void underneath stays ventilated.

Will a radon sump make my home colder?

A sump draws air from under the floor rather than from the rooms, so it shouldn't create draughts indoors. Ask the installer about the fan's running cost and noise.

Do I need to retest after insulation?

If the home is in an Affected Area, a fresh three-month test once the work is finished is sensible. If a radon system is fitted, contact UKHSA to see if you're eligible for a free retest.