Does blown-in insulation attract mice or pests in New Brunswick? | Insulation IQ?

Pest attraction is one of the most common concerns New Brunswick homeowners raise about blown-in insulation, and the answer depends significantly on the material type and the condition of your building envelope. Understanding the difference between fiberglass and cellulose blown-in insulation — and what actually draws pests into attics and walls — helps put this question in the right context.

Fiberglass blown-in insulation does not attract mice or insects. Glass fibres have no organic content and nothing edible or nutritious for rodents. Mice do not seek out fiberglass as a food source, and it does not retain moisture in a way that supports insect colonies. That said, mice will absolutely nest in fiberglass if they gain access to your attic or wall cavities. The material is soft, compressible, and warm — ideal nesting conditions. So fiberglass doesn't attract pests, but it does not repel them either. Once inside, mice will use it freely.

Cellulose blown-in insulation is made from recycled paper and wood fibre, which some homeowners assume would be a direct food source for rodents. In practice, treated cellulose is not particularly attractive to mice as food. The boric acid and other fire-retardant chemicals used to treat all CAN/ULC-S703-certified cellulose also act as a mild insecticide and desiccant. Insects like cockroaches, ants, and silverfish that come into contact with cellulose in adequate concentrations can be deterred or killed by the boric acid. This is one of the understated advantages of cellulose: it has inherent pest-deterrent properties that fiberglass lacks.

However, rodents are a different story. Mice and squirrels are not deterred by boric acid at the concentrations present in cellulose insulation. They will nest in cellulose just as readily as in fiberglass if they have access. This is a common issue in older New Brunswick homes in Fredericton, Woodstock, and rural areas where gaps around the foundation, soffits, or roof penetrations provide easy entry points.

The real issue is building envelope integrity, not insulation type. Both blown-in fiberglass and cellulose are reactive — they respond to the access conditions of your home. If you have gaps where the sill plate meets the foundation, open soffits, deteriorated fascia boards, or unsealed plumbing penetrations in the attic floor, pests will find their way in regardless of what insulation is present. A professional insulation job in New Brunswick should include an inspection of common entry points before and during installation.

Some specific vulnerabilities common in NB homes include:

• Soffit vents without screening — standard in many homes built before the 1990s, these allow both insects and small rodents to enter the attic.
• Gaps around service entries — cable and electrical conduit penetrations through the rim joist or roof deck are favourite entry points for mice.
• Deteriorated wood at the roof-wall intersection — common in older Saint John and Moncton homes with complex rooflines.
• Uncapped chimneys or attic hatches with poor seals — wildlife entry points in rural New Brunswick.

One practical consideration specific to dense-pack blown-in cellulose is that when installed at proper density (approximately 48–56 kg/m³) in wall cavities, it is physically difficult for mice to tunnel through. This is a genuine structural advantage over fiberglass batts, which offer almost no physical resistance to rodents. Properly dense-packed cellulose in a wall cavity can limit rodent movement even if they do gain access to the stud bay from another location.

For attic insulation — where blown-in material sits at a loose density — this advantage disappears. A mouse can run across the surface of either material equally easily.

In summary: blown-in insulation does not attract pests in any meaningful way, but it will not stop them if your building envelope has openings. The best pest-control strategy is thorough air sealing and mechanical exclusion (screening, caulking, and flashing) at the same time as insulation is installed. Cellulose has a mild edge on insect deterrence. For rodent resistance specifically, dense-pack wall applications offer better physical resistance than batt or loose attic applications.

If you're dealing with existing pest damage in your insulation, remediation and reinstallation is best handled by a professional. New Brunswick Insulation's directory lists contractors across the province who can assess your situation and recommend the appropriate approach.

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