Toronto (Lawrence Park): a musty smell upstairs turned out to be mold on the roof sheathing

1The Problem

A musty smell with no visible source is one of the most common reasons GTA homeowners call us, and it almost always points up. This attic had no vapour barrier anywhere in the assembly — so attic air, and the musty odour it carried, was leaking straight down into the living space, while household moisture drifted up into the cold attic. Once wood stays damp, mold follows.

2What the Inspection Found

Our inspection confirmed it: mold staining across roughly 350 sq ft of the roof sheathing, insulation far below today’s R-60 standard, uninsulated knee-wall surfaces, blocked intake ventilation, and a bathroom exhaust that wasn’t venting properly to the exterior. And critically — no vapour barrier. With nothing separating the house from the attic, air moved freely in both directions: musty attic air seeping into the bedrooms, warm humid house air condensing on the cold roof. That finding drove the whole plan — it’s exactly why we specified closed-cell spray foam across the attic floor, to seal the ceiling and act as the vapour barrier this house never had.

3How We Fixed It

This attic needed a full reset, not a top-up:

• Removed all 1,000 sq ft of contaminated insulation, bagged and disposed of safely
• Completed our 3-stage mold remediation on the affected sheathing — botanical cleaning and spore removal, wood appearance restoration, and a salt-based protective sealant to resist regrowth
• Applied 2″ of closed-cell spray foam across the attic floor — a seamless air seal and the vapour barrier this attic never had
• Spray-foamed a further 600 sq ft sloped-ceiling section, with the drywall removed and replaced
• Installed 20 baffle vents with soffit cover-up, a tower roof vent, and a dedicated bathroom roof vent so moisture finally exits the house
• Fitted a new insulated attic hatch and blew fresh fiberglass up to R-60

4The Result

The musty smell is gone because the cause is gone: the mold was remediated and sealed, the moisture source was rerouted outside, and the new spray-foam vapour barrier keeps house air out of the attic. From a few inches of century-home insulation to a sealed R-60 assembly — covered by our 10-year workmanship warranty.