Scope · and the three sentences that settle it

Mould removal after water damage: what Health Canada actually says

Mould remediation is where a water damage job stops being about water, and it is the part of the subject most heavily sold and least well explained. It is also, unusually, a subject where the Canadian government publishes clear thresholds that settle most of the arguments.

Three of Health Canada’s statements will save a homeowner more money than anything else on this site: clean it regardless of species, do not test the air, and here is the size above which you should not be doing it yourself.

The three sizes, drawn to scale

Three square metres is about the area of a single sheet of drywall. That is a usefully concrete way to think about it: if the affected area is bigger than one sheet of drywall, Health Canada recommends a qualified professional assess and clean it.

Below that, the guidance is more permissive than the industry tends to suggest. A small area is three or fewer patches, total area under 1 square metre and a homeowner can clean it using proper procedures. A medium area is more than three patches, or patches over 1 square metre but under 3 square metres, where professional assessment is recommended but homeowner cleanup is often still acceptable.

Why nobody needs to know which mould it is

This is the single most expensive misconception in the category. There is no test result that changes the instruction, because the instruction is the same for every species: control the moisture and clean the growth.

Health Canada’s reasoning is that an air test does not provide information that can predict health effects and often offers little information on the cause of the mould damage. A systematic visual inspection that finds the moisture source is worth more than a sampling report.

Which is not to say nobody should ever sample. It is to say that sampling sold before anyone has found the water is the wrong order, and that “we need to test to know what we are dealing with” is not what Health Canada says.

Where the restoration standard hands over

There is a specific moment in a water damage job where the applicable standard changes, and knowing it is useful because the scope and the price change with it.

ANSI/IICRC S500 instructs the restorer that where mould growth is discovered or suspected, they refer to ANSI/IICRC S520, Standard for Professional Mold Remediation. A contractor who keeps writing the job as a drying job after mould has been found is off their own standard; one who moves to remediation without a finding has escalated the job.

The category of the original water matters here too, because it predicts what will be found. Category 3 water — sewage, seawater, rivers — means porous materials are removed rather than dried, and removal is also what eliminates the substrate mould would grow on.

What it costs, and why we are not telling you

Every other page answering this question publishes a table of average remediation prices per square metre or square foot. We have not measured Canadian remediation prices and we are not going to synthesize a figure, for the same reason set out on the cost page.

What can honestly be said about the drivers:

• Area, measured against Health Canada’s bands. The small / medium / large split is the first thing that changes the scope.
• Containment. Larger jobs need the work area isolated and negative air, which is equipment and labour rather than materials.
• What the substrate is. Mould on a painted concrete wall and mould in insulation behind drywall are different jobs.
• Whether the moisture source is fixed. Remediating without fixing the source buys you a repeat, which is the most expensive outcome available.
• Asbestos, in a pre-1990 home. One company’s published figure for testing is $150–$400 — theirs, named, not an average.

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