Inspection

Mould

A type of fungus that grows in damp, humid conditions and can be found on walls, ceilings, in basements, around windows, and inside HVAC systems. In homes, mould is usually caused by moisture problems -- leaking roofs, foundation cracks, poor ventilation, or plumbing issues. While some moulds are harmless, others can cause health issues, especially for people with respiratory conditions.

Why It Matters

Mould is both a health concern and a symptom of a larger moisture problem. Cleaning visible mould without fixing the source is like putting a bandage on a leak. If an inspection reveals mould, the real question is: where is the moisture coming from? Addressing the root cause is essential, not optional.

Real-World Example

A buyer inspecting a townhouse in Ajax notices a musty smell in the basement. The home inspector finds visible mould growth behind the furnace and along the bottom of the basement drywall. A mould remediation company assesses the area and identifies the source as a slow foundation leak that has been wetting the drywall for months. The remediation cost is estimated at $3,000 to $5,000, including removing affected drywall, treating the area, and repairing the foundation crack. The root cause -- the leak -- must be fixed first, or the mould will return.

Ontario & GTA Context

Ontario does not have specific residential mould regulations, but landlords are required to maintain rental properties in a state of good repair under the Residential Tenancies Act, which includes addressing mould caused by building deficiencies. For home purchases, mould is not typically tested during a standard home inspection -- buyers need to request separate mould testing if they suspect an issue. In the GTA, basements are particularly susceptible to mould due to the region's high water table and humidity levels.

How It Works in Practice

If you smell mustiness or see discoloration during a viewing, raise it with your inspector. Mould testing costs $300 to $600 for air quality sampling. If mould is confirmed, the key question is the source of moisture. Addressing the moisture source is essential -- simply cleaning visible mould without fixing the underlying water problem is ineffective and the mould will return.

Common Questions

Is mould a deal breaker when buying a house?▾

Not necessarily. Small areas of mould caused by condensation or minor leaks can be remediated for a few thousand dollars. However, extensive mould from chronic water infiltration can be very expensive to fix and may indicate deeper structural or waterproofing problems. The severity and root cause determine whether it is a deal breaker.

How much does mould remediation cost in Ontario?▾

Small-scale mould remediation in Ontario typically costs $1,500 to $5,000. Larger projects involving multiple rooms or significant structural areas can cost $10,000 to $30,000 or more. The cost depends on the extent of contamination, accessibility, and whether structural repairs are needed.

Does mould affect home value?▾

Yes. Known mould issues can reduce a home's market value and deter buyers. Sellers are expected to disclose known mould problems. However, a home with a documented remediation and the underlying moisture issue resolved can regain its full value, especially if the work was done by a certified remediation company.

Related Terms

Related Guides

Home Inspection Costs

Need Guidance?

Get a second opinion on your real estate situation. No pressure, no obligation.

The RAZZ Report

Market insights and practical advice delivered to your inbox.