What is the expected lifespan of spray foam attic insulation versus blown-in fibreglass in New Brunswick's freeze-thaw climate?

Both spray foam and blown-in fibreglass can last 20-30+ years in New Brunswick attics when properly installed, but they age differently due to our Maritime freeze-thaw cycles and moisture conditions.

Closed-cell spray foam typically maintains its R-value and structural integrity for 25-30+ years in NB attics. The rigid cellular structure resists settling, moisture absorption, and thermal cycling. However, spray foam can develop hairline cracks over time as the roof structure moves through freeze-thaw cycles — NB experiences roughly 40-60 freeze-thaw events per winter, causing roof sheathing and framing to expand and contract repeatedly. These micro-cracks don't significantly reduce insulation performance but can create minor air leakage paths. Quality spray foam installation with proper thickness (minimum 2 inches for closed-cell) minimizes this issue.

Open-cell spray foam in attics has a shorter effective lifespan of 15-20 years in NB's climate. The softer, more flexible structure is more susceptible to moisture absorption during our humid summers, and repeated freeze-thaw cycles can cause gradual degradation. Open-cell foam also requires a separate vapour barrier on the interior side, and any failure of this barrier allows moisture migration that accelerates foam degradation.

Blown-in fibreglass maintains its insulating properties for 20-25 years but settles 10-15% over the first 5-10 years, reducing its effective R-value from the initial installation. In NB's high-humidity Maritime climate, fibreglass can absorb moisture during summer months, though it dries out during winter heating seasons. The material itself doesn't degrade, but rodent intrusion and air movement through the insulation can create voids over time. Fibreglass performs best when the attic floor is thoroughly air-sealed before installation — unsealed air leaks cause convective loops that reduce the insulation's effectiveness regardless of age.

Blown-in cellulose often outperforms fibreglass longevity in NB attics, lasting 25-30 years with 15-20% settling. The borate fire retardant treatment provides natural pest resistance, and cellulose's moisture-buffering properties help it handle NB's humidity swings better than fibreglass.

NB-specific factors that affect lifespan include ice dam formation (indicating heat loss through the insulation), wind washing in coastal areas where persistent winds blow through loose insulation, and the thermal stress from our 4,800-5,200 heating degree days annually. Attics that experience regular ice dams show accelerated insulation degradation because the underlying air sealing and insulation system is failing.

Practical considerations: Spray foam's higher upfront cost ($3.50-$7.00 per square foot vs $1.25-$3.00 for blown-in) is partially offset by its longer effective lifespan and superior air sealing properties. However, blown-in insulation can be easily topped up as it settles — adding 2-4 inches of new material every 15-20 years costs $800-$1,500 and restores full R-value. Spray foam cannot be easily supplemented and requires complete removal and reinstallation if replacement becomes necessary.

When to hire a professional: Both materials require professional installation for optimal lifespan. DIY blown-in installations often have uneven coverage and inadequate density, reducing both initial performance and longevity. Spray foam absolutely requires professional installation — improper mixing ratios or application thickness can cause premature failure, persistent odours, and potential health concerns.

For maximum lifespan in NB's climate, prioritize thorough air sealing of the attic floor before installing any insulation type, ensure proper attic ventilation to manage moisture, and consider a blower door test to verify the building envelope performance that protects your insulation investment.

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