Why Insulation Type Matters in Canada

Canada's climate zones range from the moderate Pacific coast to the subarctic conditions of the Yukon and northern Ontario. The National Building Code of Canada sets minimum effective thermal resistance (RSI) values for building envelopes, but the optimal level often exceeds these minimums in practice, particularly for new construction or major retrofits.

Insulation material affects more than just thermal resistance per inch. Moisture behaviour, air permeability, fire response, and installation complexity all vary by type. A product that works well in a ventilated attic may be completely inappropriate for a below-grade wall, even if its RSI value looks similar on a datasheet.

Fiberglass Batt Insulation

Fiberglass batts are the most common residential insulation material across Canada. They are sold in widths sized to fit standard 16-inch and 24-inch stud and joist spacing, which makes them straightforward to install during new construction or open-wall renovation.

Typical Applications

Above-grade wall cavities, attic floors between joists, and basement rim joists are the most frequent locations for fiberglass batts. They are not suitable for areas where moisture contact is likely, since wet fiberglass loses most of its insulating value and takes a long time to dry.

Performance Considerations

Fiberglass batts are air-permeable, meaning they do not stop air movement on their own. An air barrier—either a polyethylene vapour retarder on the warm side or a housewrap on the exterior—is required to achieve effective performance. Improper installation with gaps, compressions, or voids reduces real-world performance noticeably below the stated RSI.

Code Reference

The National Energy Code of Canada for Buildings (NECB) and provincial codes set minimum RSI requirements that vary by climate zone. RSI 5.6 to RSI 8.6 for attics is common across most of Canada's populated regions, though higher values are often cost-effective in colder zones.

Cellulose Insulation

Cellulose is made from recycled paper fibre treated with borate compounds for fire and pest resistance. It is installed either by blowing loose-fill into attic floors or by dense-packing into wall cavities through small holes drilled from the interior or exterior.

Dense-Pack Retrofits

Dense-pack cellulose is one of the more practical options for adding insulation to existing wall cavities without removing the interior wall finish. Holes approximately 50–65 mm in diameter are drilled at regular intervals, and the cellulose is packed to a density high enough to prevent settling. The holes are then plugged and the exterior cladding or interior finish is repaired.

Moisture Behaviour

Cellulose has a higher capacity to absorb and redistribute moisture compared to fiberglass, which can be an advantage in managing seasonal humidity fluctuations. However, it must be kept dry during installation and should not be used in locations with persistent moisture sources. Wet cellulose compacts and can lose a meaningful portion of its RSI value.

Spray Polyurethane Foam

Spray foam is applied as a liquid that expands and hardens in place. Two main types are used in residential construction: open-cell foam, which remains soft and flexible, and closed-cell foam, which cures rigid and dense.

Closed-Cell Foam

Closed-cell spray foam provides the highest RSI per inch of any common insulation material, roughly RSI 1.1 per 25 mm. It also acts as an effective air barrier and vapour retarder at sufficient thicknesses. These properties make it useful for rim joists, crawlspace walls, and areas where achieving a high RSI value in a thin assembly is important.

Open-Cell Foam

Open-cell foam expands significantly and fills irregular cavities well. Its RSI per inch is lower than closed-cell, approximately RSI 0.6 per 25 mm, and it is vapour-permeable. A separate vapour retarder may be required depending on the climate zone and position in the building assembly.

Installation and Cost

Spray foam requires professional installation with appropriate protective equipment. It costs substantially more per unit area than fiberglass or cellulose. In situations where its combination of air sealing, moisture resistance, and RSI in tight spaces is genuinely needed, the additional cost can be justified by reduced heating loads. For straightforward attic top-ups, other materials are generally more cost-effective.

Rigid Foam Board

Rigid foam boards—typically expanded polystyrene (EPS), extruded polystyrene (XPS), or polyisocyanurate (polyiso)—are used in applications where batt or loose-fill materials are not practical: basement wall interiors, under concrete slabs, continuous exterior insulation over wall sheathing, and cathedral roof assemblies.

Continuous Exterior Insulation

Adding a layer of rigid foam outside the structural wall sheathing eliminates thermal bridging through studs. Studs conduct heat much more readily than insulated cavities, and in a standard 2×6 wall, the framing can account for a meaningful fraction of the wall area. A continuous layer of EPS or polyiso on the exterior side reduces this bridging effect and can improve the overall effective RSI of the assembly considerably.

Below-Slab and Basement Use

XPS and EPS are both used under concrete slabs and against below-grade foundation walls. XPS is resistant to moisture absorption in ground contact, which is relevant for below-slab applications. EPS, particularly higher-density grades, is also used in these locations and tends to be less expensive.

Practical Note

Rigid foam used on the interior side of a basement wall requires a thermal barrier such as 12.7 mm drywall in occupied spaces, as most foam products are combustible. Building code requirements on this point are consistent across Canadian jurisdictions, though specific details vary.

Mineral Wool (Rock Wool and Slag Wool)

Mineral wool products are made from molten rock or industrial slag spun into fibres. They are available as batts and as rigid boards. Mineral wool is non-combustible, which simplifies some building assemblies, and it performs reasonably well when damp compared to fiberglass. It is less common than fiberglass in residential work but is used frequently in commercial construction and in residential applications where fire performance is a priority.

Comparing Options by Location

The table below summarizes typical material choices by location in a Canadian home. These are general starting points; specific projects require review against applicable building code requirements and the existing building assembly.

  • Attic floor: Blown cellulose or blown fiberglass for top-up work; batts for new construction with clear joist access.
  • Attic sloped ceiling (cathedral): Closed-cell spray foam or rigid board where rafter depth is limited; batts with adequate ventilation channel in deeper rafters.
  • Above-grade walls (new): Fiberglass or mineral wool batts in cavity, with option to add continuous rigid foam exterior.
  • Above-grade walls (retrofit, closed cavity): Dense-pack cellulose or dense-pack fiberglass.
  • Basement walls (interior): Rigid foam board with drywall finish, or closed-cell spray foam for rim joist and irregular areas.
  • Below slab: XPS or higher-density EPS rigid board.
  • Crawlspace walls: Rigid foam or spray foam depending on conditioned vs. unconditioned strategy.