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Open-Cell or Closed-Cell Spray Foam for Kamloops's Climate

Closed-cell for rims, crawl spaces, roofs and metal; open-cell for walls. R-value per inch, vapour barrier and thermal barrier rules for Kamloops.

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Home › Guides › Open-Cell or Closed-Cell Spray Foam for Kamloops's Climate

Two foams, two jobs

Open-cell and closed-cell spray foam are both polyurethane, but they behave like different materials once cured. Closed-cell is dense and rigid; a Canadian product such as Elastochem's Insulthane Extreme is rated R-6.03 per inch (LTTR at four inches), has an air permeance of 0.002 L/s per square metre at 75 Pa, and holds CCMC evaluation 13697-L. Huntsman's Heatlok Soya HP lists 2.06 RSI (R-11.68) at 50 millimetres, 37 psi compressive strength, and is sold as insulation, air barrier, vapour barrier and rain screen in one. Open-cell is soft and light; Elastochem's Insulthane 450 NM is rated R-3.8 per inch at 90 days and has a vapour permeance of 535 ng/(Pa·s·m²), roughly nine times what the code allows for a vapour barrier.

That permeance number is the whole decision in a cold climate. Open-cell lets water vapour through and needs a separate vapour barrier on the warm side; closed-cell, at sufficient thickness, is the vapour barrier.

Kamloops winters and the vapour barrier rule

Kamloops is semi-arid, with a January mean of minus 2.7 degrees, a record low of minus 38.3, and a code design temperature of minus 23. In that cold, warm indoor air pushes moisture outward through the wall, and if it reaches a cold surface it condenses. The BC Building Code 2024 handles this in Subsection 9.25.4: every thermally insulated wall, ceiling and floor needs a vapour barrier (9.25.4.1), the barrier must have a permeance not greater than 60 ng/(Pa·s·m²) by the dry-cup test (9.25.4.2.(1)), and where foamed plastic insulation is the vapour barrier it must be thick enough to meet that number (9.25.4.2.(8)). The barrier goes on the warm side (9.25.4.3).

In practice: closed-cell foam on a rim joist, crawl space wall, or metal shop skin is insulation and vapour barrier together, and the contractor specifies the thickness that meets the permeance limit for that product. Open-cell in a 2x6 wall gets poly or a vapour-retarder primer on the inside face, the same as batts. Mixing them up, such as open-cell against a cold metal roof, is the mistake that produces wet foam by February.

Hot summers, smoke and air sealing

The other half of the Kamloops year is a July mean of 21.9 degrees and a record 47.3 degrees on 29 June 2021, with wildfire smoke in the valley most summers; the City's own wildfire page notes that in the summer of 2021 wildfires threatened homes within city limits. Smoke and heat get into a house the same way January cold does, through leaks at rim joists, top plates, pot lights and the attic hatch. Both foams seal those paths. The difference is that closed-cell also adds insulation value in the shallow spots where there is no room for anything else, and it does not absorb moisture, which matters in a crawl space that sees spring runoff.

For a vented attic in Brocklehurst or Aberdeen, the usual Kamloops approach is a thin closed-cell or open-cell air-seal layer on the ceiling plane, then blown-in insulation to reach the Zone 5 target of RSI 8.67 (about R-49). For a cathedral ceiling, closed-cell against the deck is the way to reach RSI 4.67 in the depth available.

Thermal barrier: the BC rule for exposed foam

Both foams burn, and the BC Building Code treats them alike. Article 9.10.17.10 says foamed plastics that form part of a wall or ceiling assembly must be protected from adjacent space in the building by an interior finish from Subsections 9.29.4 to 9.29.9 (drywall is the everyday case), by sheet metal at least 0.38 millimetres thick with a melting point of at least 650 degrees where the building has no residential major occupancy, or by a thermal barrier meeting Sentence 3.1.5.15.(2). The article exempts foam facing concealed spaces within attic or roof spaces, crawl spaces, wall assemblies and ceiling assemblies.

The US term ignition barrier does not appear in the BC article; BC works with interior finish or thermal barrier. What it means on a Kamloops job: foam in a closed crawl space or inside a wall cavity is covered by the exemption, foam left exposed in a heated shop, a garage or a basement gets drywall or a rated intumescent coating, and the quote should say which. The contractor we connect you with prices the barrier with the foam, not as a surprise at inspection.

Where each foam goes in a Kamloops house

Closed-cell: rim joists and sill plates, crawl space walls, cantilevered floors in Westsyde and Rayleigh homes, cathedral ceilings, garage ceilings under bedrooms, and every metal building from Barnhartvale to Barriere. Open-cell: 2x6 wall cavities in new builds and renovations, interior walls for sound, and ceiling-plane air sealing where depth is not a constraint. Many houses use both, and a quote that names the product, the thickness and the effective R-value for each area is the one to keep.

Need it hauled or installed?

Call (778) 765-0272 or request a call back. This website connects Kamloops homeowners and builders with a local, licensed and insured spray foam insulation contractor. Calls and form submissions go directly to that contractor, which quotes and completes the work.

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Attic Spray Foam

Air-seal and insulate the attic in one pass, including the cathedral ceilings batts cannot handle.

Crawl Space and Rim Joist

Cold floors and damp crawl spaces are a rim joist and crawl wall problem, and foam is the standard fix.

Shops, Garages and Pole Barns

Metal buildings and detached shops, foamed so they can be heated in January.

New Builds and Renovations

Foam for builders: open-cell walls, closed-cell rims, and the schedule that goes with them.

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