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

The short version

Radon is invisible, odourless, and the second leading cause of lung cancer in Canada. It's also something that can be measured, managed, and disclosed — and increasingly, it's 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 levels in any given home depend on the local geology, the construction of the house, and how well it's ventilated.

The problem is that 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 very different readings — testing the home you're buying (or selling) is the only reliable approach.

Health Canada's action level is 200 Bq/m³. Above that threshold, 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 way to handle it. 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 the heating season is the most reliable. Be skeptical of short-term tests (48–96 hours) used to make mitigation decisions — they're less accurate.

What if the home has a mitigation system already installed? That's actually a good sign. It means the previous owners took the issue seriously. Ask for documentation of the system installation and the post-mitigation test result. Then plan to retest after you move in to confirm the system is still working correctly — mitigation fans can degrade over time.

If you don't get to test before closing, budget for testing in the first month after you move in. A long-term test 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 not knowing.

If you're selling a home

Test before you list. This gives you control over the situation. If levels are low, you have something positive to disclose. If they're elevated, you can mitigate before buyers find out on their own — and then legitimately market the home as "radon mitigated."

Buyers are increasingly radon-aware, and more real estate agents are recommending (or requiring) radon testing as part of the purchase process. A result that surprises buyers during conditional testing can delay or derail a deal. Finding out on your own terms, before the property is listed, is much better.

Do you have to disclose radon? Disclosure requirements vary by province. In some provinces, sellers are required to disclose known material defects — and a known elevated radon reading could be considered one. Consult your realtor about what applies in your jurisdiction. As a general principle, erring on the side of disclosure 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 will appreciate the transparency, and a well-documented mitigation is a feature, not a liability.

How radon affects home value

This is a reasonable 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 lead to significant price renegotiation. But a home that has been tested, found to have elevated levels, 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 tested.

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

Practical steps for real estate transactions

Buyers:

1. Include a radon test condition in your offer if possible
2. Use a long-term test (90+ days) for the most accurate result, or accept that a short-term test is a starting point only
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 your home 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 documentation
3. Disclose what you know; consult your realtor about your province's specific requirements
4. Market a mitigated home as a feature, not a liability

Finding help

If you're in a real estate transaction and need a radon test or mitigation completed quickly, a certified professional can help. Professional testing (using continuous electronic monitors) produces faster results than mail-in kits, which is useful when you're working against a closing deadline.

You can find certified radon professionals in your area on RadonFinder.ca.