Does the Maritime climate in Saint John make open-cell or closed-cell spray foam a better choice for exterior walls?

For Saint John's Maritime climate, closed-cell spray foam is the superior choice for exterior walls due to its vapour barrier properties and resistance to the high humidity that comes off the Bay of Fundy year-round.

Saint John's location on the Bay of Fundy creates unique moisture challenges that make vapour management absolutely critical. The city experiences persistent humidity from the maritime air masses, plus dramatic temperature swings as weather systems move in from the Atlantic. When warm, moist interior air migrates through wall assemblies and hits cold exterior sheathing during NB's long heating season, condensation is inevitable without proper vapour control.

Closed-cell spray foam at 2-3 inches thickness provides R-12 to R-21 while simultaneously acting as the vapour barrier, air barrier, and structural reinforcement. This eliminates the need for separate 6-mil polyethylene vapour barriers that are difficult to install perfectly in renovation projects. In Saint John's older housing stock — much of it built in the 1960s-1980s with minimal insulation — closed-cell foam can transform drafty, cold exterior walls into high-performance assemblies.

Open-cell spray foam, while less expensive at $1.50-$3.50 per square foot versus $3.50-$7.00 for closed-cell, is vapour-permeable and requires a separate interior vapour barrier in New Brunswick's Climate Zone 6. This creates installation complexity and potential failure points. If the separate vapour barrier has even small gaps or tears, Saint John's humid air will reach the cold wall cavity and condense, potentially causing hidden mould and rot that may not become apparent for years.

The Bay of Fundy's extreme tides and persistent winds also increase air infiltration rates through building envelopes. Closed-cell foam's superior air sealing properties — it bonds directly to framing lumber, electrical boxes, and plumbing penetrations — addresses this challenge better than open-cell foam, which still allows some air movement.

For a typical Saint John home, budget $4,000-$8,000 for closed-cell spray foam on exterior walls (assuming 800-1,200 square feet of wall area). While the upfront cost is higher than open-cell or dense-pack cellulose alternatives, the moisture protection is invaluable in Saint John's climate. Many Saint John homes near the harbour or on the hillsides overlooking the Bay of Fundy have experienced moisture problems from inadequate vapour barriers in wall assemblies.

This is definitely professional-only work — spray foam requires heated application equipment, proper mixing ratios, and respiratory protection. Off-ratio foam can cause persistent odours and shrinkage. Always hire experienced spray foam contractors with manufacturer training certifications and verify they carry liability insurance and WorkSafeNB coverage.

Need help finding a qualified spray foam contractor in the Saint John area? New Brunswick Insulation can match you with local professionals who understand Maritime climate challenges and have experience with both heritage homes in the uptown core and newer construction in the surrounding communities.