Why the Choice of Material Matters
Not all insulation performs the same way in all locations. A product that works well in a dry basement wall may be unsuitable in a vented attic. Canadian homes face a demanding range of conditions — below-freezing winters, humid summers, and the mechanical stress of repeated freeze-thaw cycles on building assemblies. Understanding the characteristics of each material helps narrow down which one fits a specific situation.
Fiberglass Batts and Rolls
Fiberglass is the most widely used insulation material in North American residential construction. It is available in pre-cut batts sized to fit standard stud and joist spacing, or in rolls for longer continuous runs.
R-Value
Fiberglass batts typically deliver approximately R-3.0 to R-3.8 per inch, depending on density. A standard 2×6 wall cavity (5.5 inches) filled with high-density batts reaches around R-21.
Where It Is Used
- Framed wall cavities (2×4 and 2×6 construction)
- Attic floors between joists
- Floor assemblies above unheated spaces
- Basement ceiling joists
Moisture Considerations
Fiberglass does not absorb water, but wet batts lose thermal performance and can hold moisture against adjacent framing if drainage is poor. In Canadian wall assemblies, a vapour retarder on the warm side of the insulation is required by most provincial building codes.
Mineral Wool (Rock Wool and Slag Wool)
Mineral wool — sold under brand names such as Roxul/ROCKWOOL — is made from volcanic rock or industrial slag that is spun into fibres. It is denser and more rigid than fiberglass and has a distinct set of performance characteristics.
R-Value
Mineral wool batts typically achieve R-3.7 to R-4.2 per inch. The higher density compared to standard fiberglass contributes to better performance at the edges of batt installation where compression can occur.
Key Differences from Fiberglass
Cellulose (Blown-In and Dense Pack)
Cellulose is produced from recycled paper — typically newsprint — treated with borate compounds for fire and pest resistance. It is installed either as loose-fill blown into open attic spaces or as dense-pack pumped into closed wall cavities.
R-Value
Loose-fill cellulose achieves approximately R-3.2 to R-3.8 per inch. Dense-pack cellulose in wall cavities is comparable in R-value per inch but significantly reduces air infiltration through the assembly, which adds to effective thermal performance.
Air Sealing Effect
Dense-pack cellulose is one of the few insulation materials that provides meaningful air resistance when properly installed. This characteristic is particularly relevant in older Canadian homes with leaky framing.
Moisture Behaviour
Cellulose can absorb and hold moisture. If a wall assembly is poorly detailed and allows prolonged wetting, cellulose can compact over time and lose R-value. Proper vapour management is important in Canadian climate zones where interior humidity is high in winter.
Spray Polyurethane Foam (SPF)
Spray foam is applied as a two-component liquid that expands and cures in place. It comes in two types with very different properties: open-cell and closed-cell.
Open-Cell Foam
Open-cell foam expands to a soft, spongy consistency. It delivers approximately R-3.5 per inch and provides good air sealing. However, it is vapour-permeable — moisture can diffuse through it — so a separate vapour retarder is typically required in Canadian wall assemblies to meet code.
Closed-Cell Foam
Closed-cell foam is rigid, dense, and delivers R-6.0 to R-7.0 per inch, the highest R-value per inch of any common insulation material. It also acts as both an air barrier and a vapour retarder in a single layer. This makes it useful in tight spaces such as rim joists, crawlspace walls, and the underside of roof sheathing where both performance and moisture control are priorities.
Closed-cell spray foam at 2 inches provides roughly the same R-value as a full 5.5-inch fiberglass batt. In locations where space is limited, this density advantage can be significant. The trade-off is cost — spray foam is substantially more expensive per R-value than most other materials.
Rigid Foam Boards (EPS, XPS, Polyisocyanurate)
Rigid foam boards are manufactured panels used for continuous insulation on exterior walls, under slabs, or in specific assemblies where batt insulation is impractical.
| Type | R-Value per Inch (approx.) | Common Use |
|---|---|---|
| EPS (Expanded Polystyrene) | R-3.6 to R-4.0 | Under slabs, exterior wall sheathing, basement walls |
| XPS (Extruded Polystyrene) | R-5.0 (nominal) | Below-grade applications, under slabs |
| Polyisocyanurate (Polyiso) | R-5.6 to R-6.5 at room temp | Roofing, exterior wall continuous insulation |
Note: Polyisocyanurate R-value decreases at low temperatures, which matters for Canadian applications where the material may be installed in locations exposed to cold. Some designers de-rate polyiso by 15–20% for cold-climate use.
Choosing Based on Location in the Home
Different parts of a building assembly call for different materials. Framed wall cavities between studs are efficient spaces for batts or dense-pack. Attic floors favour blown-in materials because they cover penetrations and irregular surfaces more completely. Basement walls below grade benefit from materials that handle moisture without degrading — typically rigid foam or closed-cell spray foam.
The National Building Code of Canada and provincial equivalents set minimum effective thermal resistance values for each building assembly type. These minimums represent the floor, not the target. In a climate like Edmonton or Winnipeg, exceeding code minimums significantly is often a cost-effective decision over the life of the building.
For guidance on incentive programs tied to insulation upgrades, Natural Resources Canada's Canada Greener Homes information pages outline federal programs that have included insulation measures.