How does open-cell spray foam perform in terms of air sealing compared to closed-cell spray foam in Fredericton homes?

Both open-cell and closed-cell spray foam provide excellent air sealing in Fredericton homes, but closed-cell offers superior moisture protection that's critical for New Brunswick's cold, humid Maritime climate.

Open-cell spray foam expands significantly during application (up to 100 times its liquid volume) and excels at filling irregular cavities, gaps around electrical boxes, and complex framing details. This expansion creates an effective air barrier at just 3-4 inches thickness, typically achieving air sealing performance of less than 0.02 CFM per square foot at 75 pascals — excellent by any standard. The foam's ability to conform around obstacles makes it particularly effective for rim joist areas, cathedral ceilings, and older Fredericton homes with irregular framing typical of 1960s-1980s construction.

Closed-cell spray foam provides equally effective air sealing but at much thinner applications — just 2 inches creates a complete air barrier. While it doesn't expand as dramatically as open-cell, its dense structure (2 pounds per cubic foot versus 0.5 pounds for open-cell) creates an impermeable seal that stops both air movement and moisture vapor. In Fredericton's climate, where winter temperatures regularly hit -20°C to -30°C and indoor humidity from cooking, bathing, and breathing creates significant vapor drive outward through wall assemblies, this dual function is valuable.

The critical difference for Fredericton homes is moisture management. Open-cell foam is vapor-permeable, meaning it allows moisture to pass through — this requires a separate vapor barrier (6-mil polyethylene) on the interior side of the assembly to prevent warm, moist indoor air from reaching cold surfaces within the wall cavity. Closed-cell foam acts as both insulation and vapor barrier in one application, eliminating the need for separate poly vapor barriers and reducing the risk of installation errors that could lead to condensation problems.

For basement walls in Fredericton homes, closed-cell is typically the better choice because it provides moisture protection against both interior humidity and potential foundation moisture while delivering R-6 to R-7 per inch in the limited space between foundation walls and finished rooms. For attic applications, open-cell can work well when properly detailed with vapor barriers, but many contractors prefer closed-cell for its simplicity and foolproof moisture management.

Cost considerations favor open-cell at $1.50-$3.50 per square foot versus $3.50-$7.00 for closed-cell in the Fredericton market, but the thinner application requirements for closed-cell can partially offset the material cost difference. Both require professional installation with heated spray equipment — never attempt spray foam as a DIY project due to chemical safety requirements and the precision needed for proper mixing ratios.

For optimal performance in Fredericton's 5,000+ heating degree day climate, either foam type should be part of a comprehensive air sealing strategy that includes sealing attic penetrations, weatherstripping, and addressing the rim joist area where floor framing meets foundation walls — often the largest source of air leakage in Maritime homes.