Should I use closed-cell or open-cell spray foam in my garage ceiling in Moncton NB?

For a garage ceiling in Moncton, closed-cell spray foam is the better choice if you're planning to heat the garage or have living space above it. Open-cell foam can trap moisture in New Brunswick's humid Maritime climate, leading to condensation problems and reduced insulation performance over time.

Closed-cell spray foam provides superior moisture control for garage applications in NB. At 2 inches thick, it delivers approximately R-14 insulation value while also acting as a vapour barrier — this dual function is particularly valuable in garage ceilings where temperature differentials between heated garage air and cold attic space create prime conditions for condensation. The closed-cell structure prevents moisture migration through the insulation, protecting the roof structure above from humidity generated by vehicles, snow melt, and temperature swings.

Open-cell spray foam absorbs moisture like a sponge, which makes it problematic in garage applications. When warm, humid air from the garage (especially when snow-covered vehicles are brought inside) contacts the cooler upper portion of open-cell foam, condensation can occur within the insulation itself. This trapped moisture reduces the foam's R-value, can lead to mould growth, and may cause the foam to sag or deteriorate over time. In Moncton's Maritime climate with high year-round humidity, this moisture risk is significant.

The cost difference is substantial — closed-cell typically runs $5-$7 per square foot installed in the Moncton area, while open-cell costs $2.50-$4.50 per square foot. However, for garage ceiling applications, the moisture protection and higher R-value per inch of closed-cell foam justify the premium. A typical two-car garage ceiling (500-600 square feet) will cost $2,500-$4,200 for closed-cell versus $1,250-$2,700 for open-cell.

Application considerations for your Moncton garage: If you're heating the garage for workshop use or vehicle protection, 2-3 inches of closed-cell foam provides excellent thermal performance and eliminates the need for a separate vapour barrier. If there's a bonus room or living space above the garage, closed-cell foam also provides superior sound dampening compared to open-cell. The air-sealing properties of closed-cell foam reduce drafts and improve the effectiveness of your garage heating system.

When open-cell might work: Only consider open-cell foam if the garage will remain unheated, you're in a very dry climate (not applicable in Maritime NB), and cost is the primary concern. Even then, you'd need a separate vapour barrier on the warm side of the insulation.

Professional installation is essential for either foam type. Spray foam application requires proper surface preparation, correct mixing ratios, appropriate thickness, and safety equipment for handling isocyanate chemicals. Licensed spray foam contractors in the Moncton area typically guarantee their work for 10-20 years when properly applied.

For your Moncton garage ceiling, invest in closed-cell spray foam — the moisture protection alone is worth the extra cost in New Brunswick's humid climate, and you'll get better long-term performance from your insulation investment.