The cost of mold removal in a basement in Ontario usually runs from about $500 for a small, surface-level job to $10,000 or more for a large one. Most finished basements with moderate growth land in the low thousands. The price depends on the area affected, the materials involved, the containment the crew builds, and any testing. Removal also fails if the water source stays. These are typical ranges, not quotes.
What basement mold removal typically costs
Published Canadian price guides give wide ranges because the jobs differ so much. RenoQuotes groups jobs by area. It puts moderate contamination of 10 to 100 square feet at $2,500 to $5,500, and major contamination over 100 square feet at $6,000 to $10,000 or more.
Use the table below as a rough guide. The figures come from those two sources and are typical ranges, not quotes. A company must inspect your basement before it can price the work.
| Job size | Typical range (CAD) | What it usually involves |
|---|---|---|
| Small, surface growth | $500 to $1,500 | Cleaning a limited area, little or no demolition |
| Moderate, 10 to 100 sq ft | $2,500 to $5,500 | Removing some drywall or trim, containment, air filtration |
| Major, over 100 sq ft | $6,000 to $10,000 or more | Wide demolition, full containment, disposal, drying |
| Whole home | $10,000 to $30,000 or more | Several rooms or the HVAC system |
Two things the table does not show. First, the cost of the water repair is separate, and it can exceed the cost of the mold work. Second, rebuilding is separate. New drywall, insulation, flooring and paint after the cleanup usually fall outside a remediation quote.
What drives the price
Area and depth of growth
Surface mold on painted concrete costs less to clean than mold inside a wall cavity. Porous material such as drywall, carpet underlay and insulation cannot be cleaned well. The crew removes it and bags it. More removed material means more labour, more disposal and more rebuilding.
Containment
Containment keeps spores from spreading to the rest of the house while the crew works. It normally means plastic sheeting, a sealed work zone, and negative air pressure with HEPA filtration. HomeStars lists containment at about $0.30 to $0.75 per cubic foot, and labour at about $75 to $100 per hour. A small job may need only a basic barrier. A large job in a finished basement needs a full sealed zone, and the price rises.
Testing and inspection
HomeStars lists inspection and testing at roughly $100 to $300 per sample. A lab test is not always needed. Health Canada’s guide to addressing moisture and mould indoors says it does not recommend testing the air for mould. It says a systematic visual inspection is usually more effective. A professional may suggest a test when a problem has no clear explanation.
A test can still be useful in two cases. A company can run a test after cleanup to check the result. A buyer or insurer may also ask for a report. Ask what the result will change before you pay for it.
Access and layout
A finished basement with low ceilings, tight corners or a narrow stair costs more to work in. Moving furniture and contents adds time. An unfinished basement with open joists is faster to treat.
Insurance
Home insurance policies in Ontario vary on mold. Some cover mold that follows a sudden covered water event, and many exclude mold from slow seepage or poor maintenance. Read your policy and call your broker before the work starts. This guide cannot say what your policy covers.
Why removal fails without fixing the water source
Mold needs moisture. Health Canada states that the underlying water or moisture problem should be fixed first, and that mold will reappear unless the cause is solved. It also lists mold that returns after cleaning as a reason to hire a professional, because it signals an unaddressed moisture source.
In Ontario basements the source is usually one of these:
- Groundwater seepage through the wall or floor joint, common in clay soils that hold water against the foundation.
- A failed or missing weeping tile, or a blocked drain.
- A cracked foundation wall that leaks during spring melt or heavy rain.
- A poorly sloped yard, or downspouts that discharge next to the house.
- A leaking window well.
- High indoor humidity in summer, when warm air meets cool concrete.
- A plumbing leak or a failed sump pump.
Remediation without a repair is a repeat cost. A company can remove the drywall and clean the studs. If the wall still seeps every spring, the mold returns and you pay again.
This is why the cleanup and the water repair often involve two different trades. A mold removal company handles containment, removal and cleaning. A waterproofing or foundation company handles the source. Some firms offer both. Check that each part of the job is named in writing. You can compare basement waterproofing companies in Toronto and foundation repair companies in Toronto alongside the mold boards.
How the work is done
A typical remediation follows this order:
- Inspect and find the moisture source, using a moisture meter where needed.
- Stop the water, or at least plan the repair before or during the job.
- Set up containment and negative air with HEPA filtration.
- Remove contaminated porous materials and bag them.
- Clean and HEPA vacuum the remaining surfaces.
- Dry the space fully.
- Check the result visually, and test only if there is a reason.
Health Canada sorts jobs by size. A small area is three or fewer patches totalling less than 1 square metre (about 11 square feet). A medium area is more than three patches, or patches between 1 and 3 square metres. A large area is a single patch over 3 square metres (about 32 square feet), and it needs expert assessment and cleanup. A professional is also advised when mold is suspected inside walls or above ceilings.
If you clean a small area yourself, Health Canada lists safety glasses or goggles, a well-fitting N95 respirator and disposable gloves as minimum protection.
What the boards show for Toronto, North York and Ottawa
The directory ranks companies by Google rating and review count. It does not do repair work and it does not endorse any company. The figures below are from our boards for 2026-10.
| Board | Companies ranked | Median rating | Median reviews | Total reviews | Under 20 reviews |
|---|---|---|---|---|---|
| Mold removal companies in Toronto | 19 | 4.9 | 76 | 2,044 | 4 |
| Mold removal companies in North York | 20 | 4.9 | 65.5 | 1,778 | 5 |
| Mold removal companies in Ottawa | 20 | 4.75 | 43 | 1,295 | 4 |
The review spread is wide. In Toronto the top of the board shows Paul Davis Toronto at 4.8 with 498 reviews and The Mold Guy at 4.7 with 309 reviews, while the board median is 76. In Ottawa, Mold Busters Ottawa shows 4.6 with 249 reviews and Paul Davis Ottawa shows 4.4 with 264 reviews. The Ottawa median is 43 reviews, lower than in Toronto and North York.
What this means for choosing:
- A rating near 5.0 on 10 reviews tells you less than 4.7 on 300. Look at the count with the rating.
- Four or five companies on each board have fewer than 20 reviews. Their ratings are less settled.
- High ratings are common, since the medians sit between 4.75 and 4.9. Read the review text for containment, communication and whether the company named the moisture source.
- The Ottawa board has fewer reviews in total, so the sample is smaller.
Because the water source decides whether removal lasts, check the related boards too. The Toronto basement waterproofing board ranks 20 companies with 3,934 reviews in total and a median of 81.5. The basement waterproofing companies in Ottawa board ranks 20 companies with 1,482 reviews in total and a median of 61. In North York, the basement waterproofing companies in North York board shows 20 companies and 3,276 reviews in total. You can also browse the mold removal trade hub for other Ontario towns.
Questions to ask before you accept a quote
- What is the measured area, and does the quote say how many square feet?
- Is containment included, and is negative air with HEPA filtration part of it?
- Which materials will you remove, and who rebuilds?
- Did you find the moisture source, and who fixes it?
- Is testing included, and what will the result change?
- Is there a written scope that lists each step and each exclusion?
- Does the company carry liability insurance? Ask for proof.
Get at least two written quotes. A price far below the others may leave out containment or disposal. A price far above the others may include rebuilding. Compare the scope line by line, not only the total.
When to act quickly
Health Canada advises a professional for a single patch over 3 square metres, for mold that returns, and for suspected hidden growth. Act fast if mold follows a flood, a sewage backup or contaminated water. Also act fast if someone in the home has asthma, a weak immune system or symptoms that persist. Dry wet materials within 24 to 48 hours where you can. A shorter wet period means less to remove and a lower bill.
Frequently asked questions
How much does basement mold removal cost in Ontario?
Typical Canadian ranges run from about $500 for a small job to $10,000 or more for a large one. Moderate contamination of 10 to 100 square feet is often quoted from $2,500 to $5,500. These are typical ranges, not quotes, and each job depends on the area, the materials and the containment.
Do I need mold testing before removal?
Not always. Health Canada does not recommend air testing for mold and prefers a careful visual inspection. A professional may still suggest a test when a smell or symptoms have no clear cause. Ask the company why a test is needed and what decision the result will change.
Will mold come back if the leak is not fixed?
Yes. Mold needs moisture, so growth returns if the water source stays. Health Canada says the moisture problem should be fixed first. A basement with seepage, a leaking window well or high humidity needs that repair as well as the cleanup.
Can I remove basement mold myself?
Health Canada says a small area, three or fewer patches totalling less than 1 square metre, can be cleaned with precautions. A single patch larger than 3 square metres, mold that returns or suspected hidden growth needs a professional.