Radon and Real Estate: What Home Buyers and Sellers Need to Know

Radon is invisible, odourless, and the second leading cause of lung cancer in Canada. It's also measurable, manageable, and increasingly showing up in real estate transactions. Whether you're buying or selling, here's what you need to know.

Why radon matters in a home transaction

Radon enters homes through cracks in foundations, gaps around pipes, and other openings in the building envelope. Because it accumulates indoors, the level in any given home depends on the local geology, the construction of the house, and how well it's ventilated.

You can't see it, smell it, or feel it. The only way to know if a home has elevated radon is to test it. And since radon levels vary so much from house to house, two homes on the same street can have completely different readings, so testing the specific home you're buying or selling is the only reliable approach.

Health Canada's action level is 200 Bq/m³. Above that, mitigation is recommended. Mitigation systems are effective, well-established, and typically bring levels down below 100 Bq/m³.

If you're buying a home

Request a radon test as a condition of purchase. This is the cleanest approach. Ask your realtor to include a radon test condition in the offer, with the test conducted before closing. If the result comes back elevated, you have options: negotiate a price reduction, require the seller to mitigate before closing, or walk away.

If the sellers have already tested and have results, ask to see them. A recent long-term test (90+ days) conducted during heating season is the most reliable. Short-term tests (48–96 hours) used for mitigation decisions are less accurate, so factor that in.

What if the home already has a mitigation system? That's actually a positive sign. It means the previous owners dealt with the issue properly. Ask for documentation: the system installation record and the post-mitigation test result. Then plan to retest after you move in to confirm the system is still performing. Mitigation fans do wear out over time.

If you can't test before closing, budget for testing in your first month. A long-term kit costs $30–$60 and takes 90 days to complete. If the result is elevated, you'll need to act, but knowing your number is always better than guessing.

If you're selling a home

Test before you list. This puts you in control. Low levels? You have something positive to mention. Elevated levels? You can mitigate before buyers find out on their own, and then you can legitimately market the home as "radon mitigated."

Buyers are more radon-aware than they used to be, and more real estate agents are recommending testing as part of the purchase process. An elevated result that surprises buyers during conditional testing can delay or kill a deal. Finding out on your own terms is better.

Do you have to disclose radon? Disclosure requirements vary by province. In some provinces, sellers are required to disclose known material defects, and an elevated radon reading can qualify as one. Talk to your realtor about what applies in your jurisdiction. Erring on the side of disclosure generally protects you legally and builds trust with buyers.

If you've had elevated results and mitigated: disclose both the original reading and the post-mitigation result. Buyers appreciate transparency, and documented mitigation is a feature, not a liability.

How radon affects home value

This is a fair question, and the honest answer is: it depends on how it's handled.

An undisclosed radon problem discovered during conditional testing can kill a deal or force a significant price renegotiation. But a home that's been tested, found elevated, and professionally mitigated with documentation doesn't necessarily sell for less. Buyers who understand radon often prefer a home with a known, solved problem over one that's never been touched.

The key is documentation: a test result, a mitigation invoice from a certified professional, and a post-mitigation test result. That paper trail protects everyone.

Practical steps

Buyers:

1. Include a radon test condition in your offer if possible
2. Prefer a long-term test (90+ days) over a short-term one for mitigation decisions
3. If the home has a system, request installation records and the post-mitigation test
4. Plan to retest after move-in regardless

Sellers:

1. Test before listing, ideally with a long-term kit during heating season
2. If results are above 200 Bq/m³, mitigate before listing and keep all records
3. Disclose what you know; confirm your province's specific requirements with your realtor
4. Market a mitigated home as a feature

Finding help

If you're working against a closing deadline and need a radon test or mitigation completed quickly, a certified professional can help. Professional testing with continuous electronic monitors produces results in 48–96 hours, which is much faster than a mail-in kit.

You can find certified radon professionals in your area on RadonFinder.ca, searchable by province and city.