What should I do about mould on insulation in my Moncton attic? | Insulation IQ?

Finding mould in your Moncton attic is alarming, but it's also one of the most common attic problems in New Brunswick — and it's almost always a symptom of a fixable underlying cause. The key is to address the mould and its root cause together, because treating the visible growth without eliminating what's feeding it will result in a return visit within one to two seasons.

Mould grows in attics when warm, humid air meets cold surfaces. In Moncton's climate, the mechanism is straightforward: humid air from the living space below finds its way into the attic through gaps around pot lights, bathroom exhaust fans, ceiling penetrations, and the attic hatch. Once in the attic, that warm moisture-laden air contacts the cold underside of the roof sheathing — which in winter sits just above freezing — and the moisture condenses. Repeated condensation cycles create persistently damp wood, and mould follows within weeks. This is not a ventilation problem first — it is an air leakage problem first. Simply adding roof vents to a leaky attic pulls in even more warm air from below and often makes things worse.

Before any remediation work begins, a thorough attic inspection is needed to identify the air bypass locations, assess the extent of mould growth, evaluate the condition of existing insulation, and check that bathroom and kitchen exhaust fans actually vent through the roof rather than terminating inside the attic (an unfortunately common situation in older Moncton homes and a massive contributor to attic mould).

For the mould remediation itself, the approach depends on the extent of growth. Surface mould on sheathing that covers less than 10 square feet is generally considered manageable without professional abatement, though most homeowners wisely hire professionals anyway given the health implications. Mould covering larger areas, or any situation where black or greenish-black growth is visible across multiple roof panels, warrants a professional mould remediation contractor. In New Brunswick, while there is no provincial licensing specifically for mould remediation (unlike asbestos), reputable contractors will follow Health Canada's guidance on indoor mould and the IICRC S520 standard for mould remediation.

Remediation typically involves containment of the attic space, HEPA vacuuming to remove loose spores, wire brushing or sanding affected sheathing, application of an appropriate fungicide (commonly borate-based solutions or commercial antimicrobial treatments), and in severe cases, replacement of badly damaged sheathing sections. After remediation, the treated surfaces are typically sealed with an encapsulant.

Mould-affected fibreglass batt insulation between attic joists cannot be cleaned and must be removed entirely. Fibreglass is not a food source for mould but it traps moisture and organic debris that mould will colonize. All contaminated insulation should be bagged, sealed, and disposed of as per Moncton's waste guidelines.

With the attic clean and dry, the permanent fix requires air sealing before new insulation is installed. Every penetration from below — pot lights, exhaust fan housings, junction boxes, plumbing and wiring chases — needs to be sealed with acoustical caulk or spray foam. The attic hatch must be weatherstripped and insulated. This work can be tedious but it is the single most important thing you can do to prevent recurrence. Bathroom exhaust fans must be ducted in rigid insulated pipe to a proper exterior roof cap, not flexible uninsulated duct that may terminate mid-attic.

Once air sealing is complete, new attic insulation should be installed to bring the assembly up to the R-50 to R-60 target appropriate for New Brunswick's Climate Zone 6. Blown cellulose or blown fibreglass are both appropriate for attic floor applications. Adequate soffit-to-ridge ventilation baffles must be maintained at every rafter bay so that air can move freely from the eaves to the ridge, keeping the roof deck dry and at uniform temperature.

From a cost perspective, professional attic mould remediation in Moncton typically runs $1,500 to $4,000 depending on severity and attic size, with re-insulation adding $1,500 to $3,500 on top. The Canada Greener Homes Grant and NB Power efficiency programs offer rebates that can offset a portion of the insulation upgrade costs, though grant programs do not cover remediation work directly.

For qualified help addressing attic mould and insulation in Moncton, the experienced professionals listed on New Brunswick Insulation understand both the remediation and the building science sides of this problem.

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Looking for experienced contractors? The New Brunswick Construction Network connects homeowners with qualified professionals:

• 3Tone Construction Ltd
• Thirty Four Renovations
• moose luxury painting
• Brunswick insulation & roofing
• Arctic Fox Construction Inc.