How often should you test your home radon levels?

Radon is a leading cause of lung cancer and is invisible and odorless.

The risk is long-term and you cannot sense it, which is what makes it easy to defer indefinitely. Health Canada notes that levels can differ between houses even when similar homes sit next door to each other, so a neighbour’s result tells you nothing about yours.

1. Choose short-term or long-term. The EPA describes short-term tests as staying in the home for two to 90 days and long-term tests for more than 90 days. Radon varies from day to day and season to season, so a long-term test is more likely to show your year-round average. Health Canada asks for a minimum of 3 months.
2. Place it in the lowest lived-in level. A basement you use often, or otherwise the ground floor, in a room that is used regularly. Not the kitchen or a bathroom.
3. Position it correctly. The EPA says at least 20 inches (about 50 centimetres) above the floor, where it will not be disturbed, away from drafts, high heat, high humidity and exterior walls.
4. Keep conditions normal, or closed for short tests. For a short-term test keep windows and outside doors closed as much as possible. For a test lasting just 2 or 3 days, close them at least 12 hours before it begins as well.
5. Send it to the lab promptly. Reseal the package and send it to the lab named on it right away once the test period ends.
6. Act on the result. If it is above your country’s action level, follow the confirmation steps in the kit or from your radon authority, then get a mitigation quote.

• There are none, which is the entire point. Radon is colourless and odourless
• A home in a mapped affected area, or a basement that is in regular use, is a reason to test sooner
• Major renovation is a reason to test again once the work is finished

• Testing an unoccupied basement rather than the lowest level you actually use
• Placing the detector on the floor, next to an exterior wall or in a draft
• Testing once, getting a low result, and never retesting: the EPA notes you may want to test again even after a result below its action level
• Assuming a new house is safe. Sweden’s radiation safety authority says radon needs to be measured in all homes regardless of how old they are

• Retest after any major renovation, and if you start living on a lower level of the home than before
• In Canada the heating season is the recommended time to test, and Sweden and Norway both specify winter windows
• If you have a mitigation system, the EPA says it is a good idea to retest every two years to be sure levels remain low

Mitigation, most often an active soil depressurization system with a fan, is specialist work. Use a certified radon professional rather than a general contractor. In the US the two national credentialing programmes are NRPP and NRSB; in Canada it is C-NRPP.