Mould is found in thousands of GTA homes during renovations every year. This thread covers causes, remediation costs, and prevention.
Common Mould Sources
- Bathroom fans venting into attic (extremely common in Ontario - causes extensive attic mould)
- Basement walls with inadequate waterproofing
- Roof leaks from failed flashing or ice dams
- Kitchen exhaust venting into walls or ceiling cavities
2026 Remediation Costs
- Small localized bathroom mould (under 10 sq ft): $500-$1,500
- Medium basement mould (10-100 sq ft): $2,000-$8,000
- Attic mould from fan issue (includes re-routing and treatment): $3,000-$12,000
- Extensive whole-house: $15,000-$40,000+
Insurance Coverage
Sudden mould from a covered event (burst pipe, roof leak) is typically covered. Gradual moisture mould from neglect is excluded. Document the cause immediately.
Prevention
Ensure bathroom fans vent to the exterior, maintain gutters, address basement moisture immediately, keep indoor humidity below 50% in summer.
LF Builders handles waterproofing and remediation: https://lfbuilders.ca
Share mould experiences and contractor recommendations at https://home.renovation.reviews