Wall Insulation.
Above-ground walls in Climate Zone 7A have to reach effective RSI 3.08 (R-17.5) without a heat recovery ventilator, or RSI 2.97 (R-16.9) with one. The airtightness requirement is a separate obligation with its own clause and its own number.
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A wall has three jobs and three different thresholds: thermal resistance, air leakage and vapour diffusion. Closed-cell foam can do all three, but only at the right thickness and in the right position — and the air barrier number quoted on most Canadian websites is not the one Alberta uses.
The 0.02 L/(s·m²) figure repeated across the industry is Ontario and NBC 2015 text, not Alberta's — we set out what NBC(AE) 2023 actually says about air barriers and where the material threshold really lives.
Three Jobs, Three Thresholds.
The reason a wall specification argument gets circular is that people mix the three requirements together. They sit in different articles, they are measured by different tests, and closed-cell foam meets them at different thicknesses.
- Thermal: effective RSI 3.08 (R-17.5) in Zone 7A with no HRV, RSI 2.97 (R-16.9) with one, from Tables 9.36.2.6.-A and -B. Effective means the assembly including framing heat flow.
- Air, material route: Sentence 9.36.2.10.(1) requires materials providing the principal resistance to air leakage to conform to CAN/ULC-S741, which is where the 0.02 L/(s·m²) at 75 Pa criterion actually sits — not in Article 9.25.3.2, which in the Alberta edition carries no number at all.
- Air, assembly route: Sentence 9.36.2.9.(1) also permits an assembly tested at 0.20 L/(s·m²) to CAN/ULC-S742, or to ASTM E2357 where the 1-in-50 hourly wind pressure does not exceed 0.65 kPa and the assembly sits on the warm side of the insulation. Red Deer's tabulated 1-in-50 wind pressure is 0.40 kPa.
- Vapour: a vapour barrier must not exceed 60 ng/(Pa·s·m²) dry cup under Article 9.25.4.2, and Sentence (8) says foamed plastic acting as the vapour barrier has to be thick enough to meet it. CAN/ULC-S705.1 sets that pass/fail on a 50 mm specimen, which is why 50 mm is the code-anchored answer.
- Continuity, which is what actually fails: Sentence 9.36.2.9.(2) requires the air barrier system to be continuous across construction, control and expansion joints, across junctions between different materials and assemblies, and around every penetration.
- Hybrid cavity work where the budget or the depth calls for it — foam at the sheathing for air control, fibre in front of it for R-value per dollar.
- Exterior foam handled against the position rules, not by eye. Sentence 9.25.5.2.(1) requires a low-permeance material to sit on the warm face, or outboard of a vented air space, or with a minimum ratio of outboard to inboard thermal resistance.
- Skylight shafts, which Sentence 9.36.2.6.(4) treats as walls rather than roofs — a detail that catches people on vaulted renovations.
How a Wall Assembly Gets Decided.
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Pick the air barrier route
Material route under CAN/ULC-S741, or assembly route at 0.20 L/(s·m²) under CAN/ULC-S742 or ASTM E2357. Red Deer's 0.40 kPa design wind is comfortably inside the 0.65 kPa ceiling the ASTM route imposes, though whether that route applies is the designer's and the authority's call, not ours.
- 02
Decide whether the foam is the vapour barrier
It can be, at 50 mm of CAN/ULC-S705.1 closed-cell. Some products also pass at 25 mm — published values include 47 and 51 ng/(Pa·s·m²) — but that is a product-specific result off a particular CCMC report, not a code entitlement. The standard only guarantees the threshold at 50 mm.
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Check the position, not just the number
Sentence 9.25.4.3.(3) says that where the same product is both insulation and vapour barrier, it has to sit close enough to the warm side to prevent condensation at design conditions. Passing the permeance test is necessary and not sufficient.
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Build to effective RSI
RSI 3.08 is an assembly figure. Continuous exterior insulation, framing fraction, and the details at corners, headers and service penetrations are all inside that number.
Frequently Asked Questions About Wall Insulation
What R-value do walls need in Red Deer?
Effective RSI 3.08, which is about R-17.5, for an above-ground wall in Climate Zone 7A with no heat recovery ventilator; effective RSI 2.97, about R-16.9, where an HRV is installed. Those come from the Zone 7A columns of Tables 9.36.2.6.-A and -B in NBC(AE) 2023. Rim joists follow the same figure under Sentence 9.36.2.6.(2), and skylight shafts follow it under Sentence 9.36.2.6.(4).Is 0.02 L/(s·m²) the Alberta air barrier requirement?
That number is real but it is not where most sites say it is. The sentence quoted everywhere — air barrier materials shall have an air leakage characteristic not greater than 0.02 L/(s·m²) at 75 Pa — is Ontario Building Code 9.25.3.2 wording, and it appeared in NBC 2015. Alberta's Article 9.25.3.2 is performance-worded and contains no number. In NBC(AE) 2023 the material threshold arrives through Sentence 9.36.2.10.(1), which requires conformity with CAN/ULC-S741, and it is that standard that sets 0.02. The distinction matters when someone is writing a specification.How thick does closed-cell foam have to be in a wall?
It depends which job you are asking it to do. As an air barrier material, roughly 25 mm is already an order of magnitude past the requirement — published Canadian products test at around 0.002 L/(s·m²) at 25 mm against a 0.020 limit. As a vapour barrier, 50 mm is the defensible answer, because CAN/ULC-S705.1 sets its 60 ng/(Pa·s·m²) pass/fail on a 50 mm specimen, so any conforming product meets the code limit at that thickness by definition. As insulation, the thickness follows from the effective RSI 3.08 target and whatever else is in the assembly.Can closed-cell foam go on the outside of the wall?
Yes, but the position rules bite in Zone 7A. Articles 9.25.5.1 and 9.25.5.2 govern low-permeance materials, and where exterior foam is used it must be on the warm face, outboard of an air space vented to the outdoors, or carry a minimum ratio of outboard to inboard thermal resistance. For a location in the 5 000 to 5 999 heating-degree-day band the published ratio is 0.30 — at least 30 percent of the assembly's thermal resistance outboard of the foam's inner face. Get that wrong and you have built a condensing plane inside a wall. There is also an exemption in Sentence 9.25.5.1.(4) for materials of at least 30 ng/(Pa·s·m²) permeance and RSI 0.7 where the location is under 6 000 heating degree days; Red Deer at 5 550 is inside that window, which is a genuinely useful and rarely cited detail.Does spray foam make a wall stronger?
Laboratory racking tests do show a gain — a Council of Forest Industries test note recorded a plywood-sheathed wall going from 13 000 N to 31 900 N of ultimate racking resistance with 44 mm of foam, and US testing shows similar multiples. But no Canadian code assigns spray foam a structural credit. Bracing and shear design is done without counting the foam, and it would be wrong to describe the gain as strength you can design around. It is a measured test result, not a design allowance.Do I still need poly on the inside?
Not if the foam is doing that job and is positioned to do it. Sentence 9.25.4.3.(3) explicitly contemplates the same product serving as both insulation and vapour barrier, subject to it sitting close enough to the warm side to prevent condensation at design conditions. What you should not do is add a second low-permeance layer on the interior of a foamed assembly without thinking about it, because that removes the assembly's remaining drying path.