What is the settling rate difference between blown-in cellulose and blown-in fibreglass over 20 years in a Fredericton attic?

Blown-in cellulose settles approximately 15-20% over its lifetime, while blown-in fibreglass settles only 2-5% — a significant difference that affects long-term R-value performance in Fredericton's climate.

The settling difference between these materials comes down to their physical properties and how they respond to Fredericton's temperature cycling and moisture conditions. Cellulose is made from recycled newspaper fibers that compress under their own weight over time, especially when exposed to the thermal cycling that occurs in NB attics where temperatures can swing from -25°C in winter to +50°C in summer. The borate fire retardant treatment adds weight to cellulose, contributing to settling as gravity pulls the fibers together.

Fibreglass, being made from spun glass fibers, maintains its loft much better over decades. The glass fibers are more resilient and don't compress as readily under their own weight. However, fibreglass is more susceptible to wind washing — where air movement through the attic can disturb loose-fill fibreglass, reducing its effective R-value even without settling.

In Fredericton's specific climate conditions, with approximately 4,900 heating degree days and significant seasonal temperature swings, both materials face thermal stress that can accelerate settling. The freeze-thaw cycles common in the Saint John River valley, combined with moisture from ice dams (common in older Fredericton homes), can cause cellulose to compact more than in drier climates.

Professional installers account for settling by initially installing cellulose at higher densities and depths. A quality cellulose installation targeting R-50 will typically be blown to R-55-60 initially, knowing it will settle to the target value. Fibreglass installations require less over-filling but need proper wind baffles to prevent air movement through the insulation.

For Fredericton homeowners, this means cellulose may need a top-up after 15-20 years, while fibreglass typically maintains its performance longer. However, cellulose offers superior air sealing properties during installation due to its ability to fill small gaps and cracks that fibreglass cannot reach. The choice often comes down to whether you prioritize long-term stability (fibreglass) or superior initial air sealing and thermal performance (cellulose).

Both materials should be installed by professionals with calibrated blowing equipment to achieve proper density and coverage, especially important given Fredericton's challenging winter conditions where any gaps or thin spots become thermal weak points.

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

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