What are the pros and cons of spray foam vs fibreglass batts in Miramichi NB? | Insulation IQ?

Choosing between spray foam and fibreglass batts is one of the most common decisions homeowners in Miramichi and throughout New Brunswick face when insulating or re-insulating their homes. Both products are legitimate and widely used — but they perform very differently, and the best choice depends on your assembly, budget, and what problems you're actually trying to solve.

Fibreglass batts have been the standard residential insulation product in Atlantic Canada for decades. They're manufactured to fit standard stud spacing (16 or 24 inches on centre), they're available at every building supply in Miramichi and surrounding communities, and they're within reach of most DIY budgets. A kraft-faced R-22 batt for a 2x6 wall cavity costs roughly .00 to .40 per square foot of wall area for materials. For a contractor-installed job, expect .50 to .50 per square foot installed, depending on the project.

The limitations of fibreglass in New Brunswick's Climate Zone 6 conditions are well-documented. Fibreglass is an air-permeable material — it slows air movement but does not stop it. Air leakage through stud cavities is responsible for a significant portion of heat loss in NB homes, and fibreglass batts simply pack the cavity without sealing the perimeter gaps at top and bottom plates, around electrical boxes, or at the sill plate. This means fibreglass-insulated walls often perform well below their nominal R-value in practice. Studies from the National Research Council of Canada have shown air-permeable insulation in leaky assemblies can lose 30 to 50% of its effective thermal performance compared to what the label R-value suggests.

Fibreglass is also susceptible to convection within the batt when temperature differentials are high — a real issue in a Miramichi winter where outdoor temperatures can drop to -25°C or colder. When the fibres are in contact with cold sheathing and warm interior air, the air within the batt circulates, reducing effective R-value. And poorly installed batts — compressed, torn, or with gaps at the edges — perform significantly worse than the rated value.

Spray foam addresses both of these limitations directly. Closed-cell spray foam at R-6.5 per inch is the most thermally efficient insulation available, and it's a complete air and vapour barrier at 2 inches. Open-cell spray foam is softer, less dense, and provides approximately R-3.7 per inch, but it also fills every cavity fully and seals gaps that batts cannot reach. Both types bond to the substrate and seal around electrical boxes, pipes, and framing irregularities in a way no batt product can.

The drawbacks of spray foam are primarily cost and irreversibility. Professional closed-cell spray foam installation in Miramichi runs .00 to .00 per square foot for a wall application, three to four times the cost of fibreglass batts. That premium is often justified in below-grade applications (basement walls, rim joists, crawlspaces) where moisture control is as important as thermal performance. In above-grade wall cavities where a proper air barrier membrane (like Typar or Tyvek) is already in place and the wall is well-sealed, the added cost of spray foam over batts is harder to justify on pure energy payback grounds.

Spray foam is also permanent. Once cured, it adheres to framing and sheathing. If you need to rewire, add plumbing, or access the wall cavity in the future, removing closed-cell foam is a messy and destructive process. Some contractors and building scientists advocate for open-cell foam in wall cavities for this reason — it's easier to cut through for future work, though it still requires a separate vapour barrier in Climate Zone 6.

A hybrid approach is increasingly popular in Miramichi new construction and deep energy retrofits: 1 to 2 inches of closed-cell foam sprayed against the sheathing for air sealing and vapour control, with R-14 or R-22 fibreglass batts filling the remainder of the stud cavity. This combines the air sealing and vapour management of foam with the cost efficiency of fibreglass, achieving R-22 to R-27 effective in a standard 2x6 wall at a total cost closer to .00 to .50 per square foot installed.

For Miramichi homeowners weighing this decision, the location matters: spray foam is almost always the better choice for basements, crawlspaces, and rim joists regardless of budget, while above-grade walls are often where fibreglass batts — installed with careful attention to air sealing at the perimeter — deliver strong value. The New Brunswick Construction Network can connect you with insulation professionals across the Miramichi region who can assess your specific assembly and give you a quote on both approaches.

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

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