Is mould remediation regulated in Ontario?

In our search of Ontario law we found no statute or regulation that governs mould remediation, licenses mould remediators, or sets indoor mould limits. With no licence to check, the quality of the work depends on what is written into the contract.

Health Canada does give homeowners a practical size guide. A small area is one to three patches, each less than one square metre. A medium area is more than three patches, or patches greater than one square metre but less than three square metres. An extensive area is a single patch larger than three square metres. Health Canada says you can generally clean small and medium sized areas yourself, and recommends getting professional help with extensive mould growth.

Because we found no regulation that sets a standard for professional remediation, the written scope of work carries most of the weight. Before anyone starts, the contract should describe exactly which areas will be treated, how the moisture source will be addressed, and what a completed job looks like. Fixing the moisture source is not optional: mould returns if the water problem stays. After the work, a post-remediation check should confirm the written scope was completed, the moisture source was repaired, and no visible mould remains.

One thing worth raising before any wall, ceiling or floor is opened in a home built before 1990: Health Canada lists drywall and floor and ceiling tiles among older building materials that may contain asbestos, and Ontario's guide lists textured paints and coatings. If the remediation involves cutting or removing any of those materials, have them tested before the work begins. A pre-renovation inspection with asbestos testing runs roughly $250 to $1,300 depending on the size of the building and the number of samples, based on published Ontario contractor prices read in September 2026.

The written contract, the agreed scope and any post-remediation report are the records to file once the job is done.