Insulation materials for northern Canada: a comparison

No single insulation material is best for every part of a northern Canadian house. The right choice depends on where it goes, how it handles moisture, the thermal resistance you can fit into the available depth, and how the assembly manages air and vapour. This overview compares the materials most commonly specified in cold-climate Canadian construction.

How thermal resistance is measured

Canadian codes express thermal resistance in RSI (metric), while product packaging often still shows R-value (imperial). The conversion is RSI 1.0 ≈ R-5.7. Both describe resistance to heat flow per unit of material; higher numbers mean more resistance. What matters in practice is the effective resistance of the whole assembly, including the reduction caused by thermal bridging through studs and framing, not just the rated value of the insulation alone.

The common materials

Fibreglass batts and blown fibreglass

Fibreglass is widely available and economical. Batts suit standard stud and joist spacing; blown fibreglass suits attics. Its resistance depends heavily on careful, gap-free installation: compressed or poorly fitted batts lose performance. Fibreglass is air-permeable, so it relies on a separate air barrier to control leakage.

Mineral wool (stone or slag)

Mineral wool batts and boards offer comparable resistance to fibreglass with added density. They are non-combustible, hold their shape well, and tolerate moisture without losing much performance, which makes them a common choice for exterior continuous insulation and rim-joist areas.

Cellulose

Made largely from recycled paper treated for fire and pest resistance, cellulose is typically dense-packed into cavities or blown into attics. Its density helps slow air movement within the cavity, though it still needs a dedicated air barrier.

Rigid foam boards

Expanded polystyrene (EPS), extruded polystyrene (XPS) and polyisocyanurate boards provide high resistance per unit thickness and work well as continuous exterior insulation to break thermal bridges. Polyiso has a high rated value but can lose some resistance at very low temperatures, a relevant consideration in northern climates.

Spray polyurethane foam

Closed-cell spray foam combines high resistance per inch with an air-sealing and, at sufficient thickness, vapour-control function in one application. It is often used at rim joists and irregular cavities. It generally requires professional installation.

Quick comparison

Material	Approx. R per inch	Air barrier on its own	Typical use
Fibreglass batt	R-3.1 to R-3.8	No	Walls, ceilings
Mineral wool	R-3.7 to R-4.2	No	Walls, exterior, rim joists
Cellulose (dense-pack)	R-3.2 to R-3.8	Partial	Walls, attics
EPS / XPS board	R-3.6 to R-5.0	No (board itself)	Exterior, foundation
Closed-cell spray foam	R-5.5 to R-6.5	Yes	Rim joists, irregular cavities

Ranges above are typical published figures; verify the rated value of the specific product you use, since formulations differ between manufacturers.

Moisture, vapour and the order of layers

In a cold climate, warm indoor air carries moisture toward the cold exterior. If that moisture reaches a surface below its dew point inside the assembly, it can condense. This is why the placement of insulation, the air barrier and any vapour-control layer is as important as the material itself. The general cold-climate principle is to keep the structure warm and dry and to avoid trapping moisture between two low-permeability layers.

Choosing for each location

• Attic: blown fibreglass or cellulose is common and cost-effective where depth is available.
• Above-grade walls: cavity insulation plus continuous exterior board to reduce bridging.
• Rim joists: mineral wool or closed-cell spray foam, which also helps seal a notoriously leaky area.
• Below grade: moisture-tolerant rigid foam against foundation walls.