How much does it cost to replace mould-damaged drywall in a GTA basement including remediation?

Replacing mould-damaged drywall in a GTA basement typically costs $3,000 to $12,000 when you include both professional mould remediation and new drywall installation, though severe cases affecting large areas can push costs to $15,000 or more. The wide range depends on how much drywall is affected, whether the mould has spread into the framing or insulation, and what caused the moisture in the first place.

The cost breaks down into two distinct phases. Mould remediation — the removal of contaminated materials and treatment of affected areas — typically runs $1,500 to $6,000 for a standard basement in the GTA. This includes containment setup (plastic barriers, negative air pressure machines with HEPA filtration), removal of all affected drywall cut back at least 600mm beyond the visible mould boundary, treatment of framing and concrete with antimicrobial solutions, and air quality testing to confirm clearance. In Ontario, mould remediation should be handled by professionals following the IICRC S520 standard, especially when the affected area exceeds 10 square feet. Smaller patches of surface mould on drywall can sometimes be addressed by a qualified drywall contractor, but anything behind the drywall — in the insulation, on the studs, or on the concrete foundation — requires a remediation specialist.

New drywall installation after remediation typically costs $1,500 to $6,000 depending on the area being re-drywalled. For a typical GTA basement of 800 to 1,200 square feet, expect $5,000 to $12,000 for the complete drywall scope including framing repairs, new insulation (minimum R-20 for below-grade walls per Ontario Building Code), 6-mil polyethylene vapour barrier, mould-resistant drywall (purple board at $24 to $32 per 4x8 sheet), taping, and a Level 4 finish. Many contractors and homeowners wisely upgrade to mould-resistant drywall during replacement rather than reinstalling standard paper-faced board that contributed to the original problem.

What most homeowners underestimate is the root cause repair cost. Mould does not grow without moisture, and installing beautiful new drywall over an unresolved moisture problem guarantees you will be doing this again in two to five years — at triple the total cost. Common root causes in GTA basements include foundation cracks allowing water infiltration ($500 to $3,000 for crack injection), failed or missing weeping tile ($8,000 to $20,000 for interior or exterior waterproofing), improper grading directing rainwater toward the foundation, missing or improperly installed vapour barrier, and condensation from inadequate insulation on cold concrete walls. The remediation contractor should identify the moisture source as part of their assessment, and that source must be corrected before any new drywall goes up.

Timing matters in the GTA. Basement floods and moisture problems peak during spring thaw (March through May) and after heavy summer rainstorms, which means remediation companies are busiest and most expensive during these periods. If you can schedule remediation and drywall replacement during the fall or winter months, you may find better availability and pricing. However, winter basement finishing requires the space to be heated above 10 degrees Celsius for proper compound curing.

For budgeting purposes, plan for the full picture: remediation ($1,500 to $6,000), root cause repair ($500 to $20,000 depending on the issue), and new drywall installation ($1,500 to $6,000). Get at least three quotes from remediation companies and separate quotes from drywall contractors — some firms handle both, but specialization often produces better results. Always confirm that your remediation contractor carries WSIB coverage and appropriate liability insurance, as mould work involves health hazards that general contractors may not be insured for.

If you are dealing with mould-damaged drywall in your basement, Toronto Drywall Installers can match you with local drywall professionals experienced in post-remediation basement finishing through the Toronto Construction Network.