How does the total installed cost of spray foam compare to blown-in insulation for a Saint John NB crawl space with irregular joists?

Spray foam will cost roughly 2-3 times more than blown-in insulation for your Saint John crawl space, but the performance difference in irregular joist spaces often justifies the premium.

For a typical Saint John crawl space (600-800 square feet of floor area above), expect blown-in cellulose to cost $1,200-$2,500 installed, while closed-cell spray foam runs $3,000-$6,000 installed. However, these numbers tell only part of the story when dealing with irregular joist spacing and the moisture challenges common in Saint John's older housing stock.

Blown-in cellulose works well in standard 16" or 24" on-center joist bays, where installers can achieve proper density and coverage. But irregular joist spacing — common in Saint John homes built before the 1960s — creates installation challenges. Blown-in insulation may not achieve proper density in odd-sized cavities, leaving gaps around bridging, cross-bracing, and where joists vary in depth. Dense-pack installation (3.5+ pounds per cubic foot) helps with air sealing, but achieving consistent coverage in irregular spaces requires experienced installers and often costs toward the higher end of the range.

Closed-cell spray foam excels in irregular joist applications because it expands to fill every gap, void, and irregular cavity completely. Two inches of closed-cell foam provides R-12 to R-14, acts as both insulation and vapour barrier, and seals all the air leakage points that make crawl spaces so problematic in Saint John's Maritime climate. The foam adheres directly to the subfloor above and rim joists, creating a continuous thermal barrier regardless of joist spacing irregularities.

Saint John's coastal location brings persistent moisture challenges that favor spray foam in crawl spaces. The city's proximity to the Bay of Fundy means high humidity, frequent fog, and soil moisture that can migrate through foundation walls. Closed-cell spray foam's moisture resistance and air sealing properties help prevent the condensation and mould problems that plague many Saint John crawl spaces, particularly in the older neighborhoods around uptown and the south end.

Consider the total system cost when comparing options. Blown-in insulation may require additional air sealing work (caulking rim joists, sealing penetrations, installing vapour barriers) that spray foam accomplishes in one application. Factor in potential crawl space encapsulation costs — sealing vents, installing ground vapour barriers, and conditioning the space — which become more critical with blown-in insulation than with spray foam's superior moisture management.

For irregular joist spaces specifically, spray foam typically provides better long-term value despite the higher upfront cost. The complete air sealing eliminates the cold floor complaints common in Saint John homes, reduces heating costs more effectively, and prevents the moisture-related callbacks that can occur with improperly installed blown-in insulation in challenging spaces.

Hire a professional for either option — crawl space insulation requires proper moisture assessment, ventilation decisions, and installation techniques that affect your home's entire building envelope. Get quotes for both approaches from experienced contractors who understand Saint John's specific moisture and foundation challenges.