Is open-cell or closed-cell spray foam better for New Brunswick homes? | Insulation IQ?

The open-cell versus closed-cell debate is one of the most common questions New Brunswick homeowners and contractors face, and the honest answer is that neither product is universally better — the right choice depends entirely on where in the building you are insulating, your performance targets, and your budget. In New Brunswick's climate zone 6 environment, the distinction matters more than it does in warmer Canadian provinces, so let's work through the key differences carefully.

Closed-cell spray foam is a rigid, dense product that cures to a firm, water-resistant shell. It delivers approximately R-6 to R-7 per inch, making it the highest R-value-per-inch product available for retrofit applications. More importantly for NB conditions, closed-cell has a vapour permeance below 1 perm at 2 inches of thickness, which qualifies it as a Class II vapour retarder under the National Building Code. This means it simultaneously air-seals, insulates, and vapour-manages in a single application — a significant advantage in assemblies where you cannot install a separate poly vapour barrier, such as a crawl space wall or a rim joist cavity. Closed-cell also adds structural rigidity to wall and floor assemblies and is completely resistant to water absorption, so a minor flooding event will not compromise the insulation.

Open-cell spray foam cures to a soft, spongy texture and delivers approximately R-3.5 to R-4 per inch. It is vapour-permeable (typically 10–20 perms), which means it functions as an air barrier but not a vapour retarder. A separate vapour barrier is required in most NB assemblies when using open-cell. The material cost is substantially lower — roughly 30–50% less per square foot than closed-cell — which makes it attractive for large-volume applications like attics or interior wall cavities where the full R-value and vapour management of closed-cell are not needed.

For a New Brunswick climate, the application location is the deciding factor. Rim joists and band joists are almost universally best served by closed-cell: the tight, bridged cavity benefits from the structural fill, vapour control, and moisture resistance, and the relatively small area means the cost premium over open-cell is modest in absolute dollars. Basement walls and crawl space walls similarly favour closed-cell because of persistent moisture pressure from the soil side — open-cell foam in below-grade contact can absorb water and lose effectiveness over time.

In attics, the calculus shifts. New Brunswick's cold winters mean attic assemblies need substantial total R-value (the NBC recommends effective R-60 in climate zone 6 under the latest energy code pathways), and achieving that with spray foam alone would be prohibitively expensive. Most contractors in Moncton, Fredericton, and Saint John use open-cell spray foam to air-seal the attic floor and all penetrations, then dense-pack the remaining depth with blown-in cellulose or fibreglass to reach code-minimum R-values at a practical cost. This hybrid approach captures the air-sealing benefit of spray foam without paying closed-cell prices for 16+ inches of attic depth.

Cathedral ceilings and unvented roof assemblies in New Brunswick require careful design. The NBC requires that a sufficient portion of the total roof assembly R-value be on the cold side of any air-impermeable insulation to keep the condensation plane above the dew point. For climate zone 6, the cold-side R-value ratio guidance generally means at least 58% of total R-value should be provided by impermeable insulation (like closed-cell) above the roof deck, or the assembly must be designed by an engineer. Open-cell alone is not appropriate for an unvented cathedral ceiling in NB without a substantial impermeable layer on the exterior.

Cost comparison for a typical Fredericton or Moncton renovation shows open-cell running roughly $0.90–$1.75 per square foot installed versus $1.75–$3.50 per square foot for closed-cell. For a 1,500 square foot attic floor, the difference between air-sealing with open-cell (2 inches) plus blown-in fill versus full closed-cell could be $3,000–$6,000 — meaningful money that is better spent on other building envelope improvements.

NB Power rebate programs and the Canada Greener Homes Grant treat both types of foam as eligible insulation upgrades when properly installed and documented. An NB Energy Advisor assessment before work begins will help you identify the highest-impact applications for your specific home.

For guidance on which product best suits your project and to find qualified professionals in New Brunswick, the New Brunswick Insulation network is a helpful resource.

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