Mould Discovered After Closing in Ontario: What Buyers Can Do

Finding mould in your new home is more than an inconvenience — it can raise real health concerns, and it often shows up in a way that makes you immediately wonder whether the seller knew and said nothing. Behind drywall, under flooring, or tucked into a basement corner, hidden mould is one of the more common post-closing disputes in Ontario resale transactions.

Mould discovered after closing raises two separate questions that are easy to blur together: what should you do right now to protect your health and your home, and what are your legal options against the seller? This article addresses both.

First Steps: Health, Safety, and Documentation

• [ ] Don't disturb the affected area more than necessary before it's documented
• [ ] Photograph and video the mould, its location, and the extent of visible damage
• [ ] Get a professional mould or moisture assessment identifying the type, extent, and likely source, such as a leak, poor ventilation, or grading issues
• [ ] Note the date you discovered it and how you found it
• [ ] If the affected area is significant or you have health concerns, address remediation with a qualified professional promptly — don't wait on the legal process before protecting your household's health

Health and safety come first; documentation supports whatever legal options you decide to pursue afterward.

Was This a Defect the Seller Had to Disclose?

Ontario's default rule for resale purchases is caveat emptor — the buyer generally bears the risk of defects that a reasonable inspection could have caught. Mould that's the visible result of an obvious, long-standing water problem may fall into that category. The analysis shifts significantly if the mould was genuinely hidden, behind finished walls or under flooring, for example, and there's evidence the seller actually knew about the underlying moisture problem, such as a past leak, a previous remediation attempt, or a written disclosure they didn't make.

Signs the Seller May Have Known

Fresh paint or repairs concentrated around a specific wall or ceiling area, a strong smell of cleaning products or air fresheners noticeable only in certain rooms, mould remediation invoices or insurance claims found in leftover paperwork, and a Seller Property Information Statement that answered "no" to a water-damage or mould-related question can all support an inference that the seller knew more than they said.

Legal Options for Recovering Your Costs

• Misrepresentation, if the seller made a false statement about water damage, leaks, or mould, including through an SPIS
• A claim tied to known, concealed latent defects, if there's evidence the seller was aware of an underlying moisture problem and didn't disclose it because it was actively dangerous or made the home unfit to live in
• A breach of a specific contractual warranty, if your Agreement of Purchase and Sale contained a relevant representation that turned out to be false

As with most post-closing defect disputes, the strength of your claim depends far more on what you can show the seller actually knew than on the severity of the mould itself.

Insurance Considerations

Whether your home insurance covers mould remediation costs depends entirely on your policy's terms, and many policies limit or exclude mould coverage, particularly where it results from long-term moisture issues rather than a sudden, identifiable event. Speak with your broker or insurer directly; this is a policy-specific question, not something Ontario law standardizes.

Building a Strong Record

Keep every document together in one place as the situation develops: your purchase agreement, any SPIS, your original home inspection report, the mould assessment, remediation quotes and invoices, and copies of any communication with the seller or their agent. A lawyer reviewing your options will need this full picture, not just the mould report on its own.

Frequently asked questions