Mold Remediation Cost in Ontario by Size of Job

Mold remediation cost in Ontario scales with the size of the affected area and where it is. A small patch under about 10 sq ft can often be handled by the homeowner for the price of supplies. Professional attic jobs in our area typically run $2,300 to $6,500, and basement jobs run $1,200 to $9,500, with the spread inside each range coming from how many square feet are involved and how much material has to come out.

How job size is measured

Size means the surface area of visible and hidden growth, not the size of the house. Health Canada's guidance treats a patch smaller than about one square metre, roughly 10 sq ft, as small. A few patches or an area up to about three square metres is moderate, and anything larger is extensive. Its general advice is that small areas can be cleaned by the occupant, and that larger areas are a job for professionals.

The catch is that visible mold is often the edge of a bigger area. A stain at the bottom of a basement wall can run the full length of the wall behind the drywall. That is why a moisture meter and a thermal camera get used before a price is fixed. Sizing the job properly is the first step in pricing it properly.

Small jobs: a patch on a wall, window frame or bathroom ceiling

Surface growth on painted drywall, tile grout, window sills or a bathroom ceiling, under that one square metre mark, is usually a cleaning job plus a ventilation fix. Detergent and water, gloves, eye protection and a properly fitted N95 respirator are the basics. Your cost is the supplies and maybe a better bath fan.

A small job turns into a paid job when the material is porous and the mold is through it. Drywall that is soft, stained on the back or wet inside the wall cavity has to be cut out. Even then, a single contained section is the least expensive professional work there is.

Mid-size jobs: one room or one wall line

This is the most common call. Think one finished basement wall, a corner where a downspout dumped water against the foundation for years, or a closet on a cold exterior wall. The work is a contained area under negative air, removal of the affected drywall and insulation, HEPA vacuuming and cleaning of the framing, and drying if the wood is still wet.

At this size a large share of the cost is fixed. Setting up containment, running a HEPA air scrubber, suiting up, bagging waste and writing the clearance report cost about the same for 30 sq ft as for 80 sq ft. That is why a mid-size job does not cost three times what a small one does, and why the cost per square foot drops as jobs get bigger.

Attic mold remediation cost by size

Attics are priced mostly on the area of roof sheathing affected, plus access. Growth limited to the north slope or to the area around a disconnected bath fan duct is a partial attic. Dark staining across the whole underside of the roof deck is a full attic. Attic jobs here run $2,300 to $6,500.

The things that move an attic price within that range:

• Square footage of sheathing and how many framing members are affected.
• Roof pitch and headroom. A low-slope attic you have to crawl through takes far longer.
• Whether insulation is contaminated or wet and needs to be removed and replaced.
• The size and location of the attic hatch, and what is below it.
• Whether a fungistatic coating is applied to the cleaned wood afterwards.

The ventilation or air-leak problem that caused the growth has to be corrected too. Sometimes that is a simple duct reconnection. Sometimes it is roofing work that a roofer prices separately.

Large jobs: full basements and crawlspaces

A fully finished basement that flooded and was left, or a crawlspace with growth across the joists, sits at the top of the range. Basement and crawlspace jobs run $1,200 to $9,500. Large jobs mean multiple containment zones or the whole level sealed off, several air scrubbers, a lot of demolition and bagging, and more days on site.

Crawlspaces cost more per square foot than open basements because everything is done lying down, and because the soil floor and vents usually need attention to keep the space dry afterwards.

What size does not tell you

Square footage sets the baseline, but two jobs of the same size can still price differently. Wet framing that needs drying adds equipment days. Finished surfaces add demolition. The rebuild afterwards is a separate cost with a separate contractor, since mitigation companies like ours stop at clean, dry framing. Why quotes from different companies differ for the same job is its own subject.

To get a number for your house, measure the visible area roughly, take photos from far enough back to show the whole wall or roof slope, and add a few close-ups. Note any musty smell in rooms with nothing visible. That is enough for a contractor to tell you which size bracket you are in and what it should cost.

Common questions