Should I test for radon gas before buying a home in Ontario, and does a seller have to disclose it?

Radon is an odourless, invisible gas that occurs naturally in soil and can seep into a home through foundation cracks and gaps, with levels varying significantly even between neighbouring properties depending on local geology and how the house is built. Because it can't be detected without testing, most sellers genuinely have no way of knowing their radon level unless they've specifically tested for it, which limits how often disclosure duties come into play compared to a visible or previously identified problem.

If a seller has actually had radon testing done and knows the result shows an elevated level, that known information generally falls within the same disclosure principle that applies to other hidden, health-affecting conditions. Because testing is inexpensive and straightforward compared to many other environmental checks, buyers concerned about radon, particularly for homes with basements used as living space, should consider arranging their own long-term test as a condition of purchase or promptly after closing, rather than assuming a clean-looking, newer-seeming home is automatically low-risk. Mitigation systems exist and are generally effective if a test does come back elevated.