Is spray foam or fibreglass insulation better for a renovation in NB?

Spray foam insulation is generally the better choice for New Brunswick renovations, especially for basements, rim joists, and air sealing applications. While fibreglass costs less upfront, spray foam's superior moisture resistance and air sealing properties make it worth the investment in NB's demanding Maritime climate.

Closed-cell spray foam is the gold standard for NB basement renovations and rim joist insulation. It provides an R-value of 6-7 per inch, creates a complete air and vapour barrier, and won't absorb moisture or support mould growth. This is critical in NB basements where spring snowmelt raises the water table and humidity swings from 30% in winter to 70% in summer. Closed-cell spray foam costs $1.50-$3.00 per square foot depending on thickness, roughly double the cost of fibreglass, but eliminates the need for separate vapour barrier installation.

Open-cell spray foam works well for interior walls and cathedral ceilings where moisture control is less critical. It provides R-3.5 per inch, excellent air sealing, and costs $1.00-$1.75 per square foot. However, it's vapour permeable and can absorb moisture, making it unsuitable for basement applications or anywhere moisture infiltration is possible.

Fibreglass batt insulation remains the most economical choice for standard wall and ceiling cavities in heated areas of the home. It costs $0.50-$1.00 per square foot installed and provides R-3.2 to R-3.8 per inch. However, fibreglass requires careful installation with proper vapour barrier placement and air sealing to perform effectively in NB's climate. Poorly installed fibreglass with gaps, compression, or vapour barrier tears performs far below its rated R-value and can trap moisture leading to mould problems.

NB Climate Considerations

New Brunswick's 100+ annual freeze-thaw cycles and dramatic humidity swings make air sealing absolutely critical for renovation success. Spray foam excels here because it seals gaps and cracks that fibreglass cannot address. Even perfectly installed fibreglass batts allow air movement through the insulation, reducing thermal performance and allowing moisture-laden air to reach cold surfaces where it condenses.

Basement applications in NB strongly favour closed-cell spray foam applied directly to foundation walls. This approach eliminates the thermal bridging and moisture problems that plague fibreglass-insulated basement walls. Never install fibreglass batts against concrete foundation walls in NB — the temperature differential causes condensation that the fibreglass absorbs, creating ideal mould conditions.

Rim joist insulation is another area where spray foam shines in NB renovations. The rim joist area is typically the leakiest part of any home's thermal envelope. Spray foam seals these gaps completely while providing insulation, whereas fibreglass requires careful cutting, fitting, and separate air sealing that's difficult to achieve effectively.

When to Choose Each Option

Choose closed-cell spray foam for: basement walls, rim joists, crawl spaces, cathedral ceilings, bonus rooms over garages, and any application where moisture control and air sealing are priorities. The higher upfront cost pays for itself through energy savings and prevents moisture problems that cost thousands to remediate.

Choose fibreglass for: standard wall and ceiling cavities in heated areas where budget is the primary concern and proper installation with vapour barrier can be ensured. Blown-in fibreglass works well for attic insulation over existing material.

Professional installation is mandatory for spray foam — this requires specialized equipment, proper ventilation during application, and knowledge of correct application thickness. DIY spray foam kits from big box stores rarely achieve the performance of professionally applied foam and can create health hazards if not properly ventilated during curing.

For most NB renovation budgets, a hybrid approach works well: use closed-cell spray foam for critical moisture-prone areas like basements and rim joists, and fibreglass for standard wall cavities where moisture control is less critical. This maximizes performance where it matters most while controlling overall insulation costs.

Need help finding an experienced insulation contractor in your area? New Brunswick Renovations can connect you with local professionals who understand NB's unique climate challenges.