Why insulation choice matters more in Canada

Canadian building codes have steadily increased minimum R-value requirements for walls, attics, and foundations over the past decade, and the reasons go beyond simple energy costs. In provinces like Alberta, Manitoba, and northern Ontario, design temperatures can sit below −30 °C for weeks at a time. Under those conditions, the wrong insulation — or the right insulation installed in the wrong location — can lead to moisture accumulation inside wall cavities, structural rot, and expensive remediation.

The National Energy Code of Canada for Buildings (NECB) and provincial amendments define minimum thermal resistance values, but those minimums are not always sufficient for older housing stock or homes located in more severe climate zones. Understanding what each insulation type actually does — not just its labelled R-value — gives a more complete picture when making a decision.

Fibreglass batts

Fibreglass batts remain the most commonly used insulation in Canadian residential construction. They are available in standard widths to fit between 2×4 and 2×6 wall studs, and in higher-density versions that provide slightly better thermal performance per inch than standard-density products.

A standard 2×6 fibreglass batt achieves approximately R-19 to R-21. That is adequate for walls in much of southern Canada under current codes, but barely meets the threshold in colder climate zones. The critical limitation of fibreglass batts is that their R-value assumes a perfect installation — no gaps, no compression, no bypasses. In practice, around electrical boxes, plumbing penetrations, and the edges of studs, batts are frequently cut poorly or left with voids that sharply reduce the effective R-value of the assembly.

Fibreglass also does not stop air movement on its own. A properly detailed air barrier — typically polyethylene sheeting or airtight drywall — is needed alongside the batt to prevent warm interior air from migrating into the wall cavity and condensing on the cold exterior sheathing.

Fibreglass batts work well when installed carefully and combined with a continuous air barrier. They are not forgiving of shortcuts.

Mineral wool (rock wool and slag wool)

Mineral wool batts — sold under brand names like Roxul and Rockwool — are made from basalt rock or industrial slag. They offer two properties that distinguish them from fibreglass: they are semi-rigid, which makes them easier to cut cleanly around obstructions, and they are inherently hydrophobic, meaning water does not penetrate the fibre matrix.

The thermal resistance of mineral wool batts is similar to fibreglass — roughly R-3.7 to R-4.2 per inch depending on density. However, because the product holds its shape better during installation, real-world performance is typically closer to the rated value. Mineral wool also provides meaningful fire resistance and sound attenuation, both of which can be relevant in attached dwellings or when insulating between storeys.

Cost is the main drawback. Mineral wool products typically cost 30 to 50 percent more than fibreglass batts of comparable dimensions. For a full house insulation job, that premium adds up. Whether the performance and handling advantages justify the additional cost depends on the specific application and the skill level of the installer.

Spray polyurethane foam (SPF)

Spray foam comes in two formulations with different performance profiles. Open-cell foam expands significantly when applied and produces a soft, flexible product with an R-value of approximately R-3.6 to R-3.8 per inch. It is permeable to water vapour. Closed-cell foam expands less, is rigid when cured, and achieves approximately R-6 to R-7 per inch. It is also largely impermeable to water vapour and provides a measure of structural reinforcement to sheathing panels.

Closed-cell spray foam is frequently used in challenging locations — rim joists, crawlspace ceilings, and under-slab applications — where its combination of high R-value per inch, air sealing, and moisture resistance is difficult to match with other products. It is also used as a continuous insulation layer on the exterior of sheathing in high-performance wall assemblies.

The installation of spray foam requires trained applicators using specialised equipment. Both components must be applied at the correct temperature and humidity for the foam to cure properly. Off-ratio mixing or application in cold conditions can result in a foam that off-gasses indefinitely, creating indoor air quality concerns. The Natural Resources Canada guidance on SPF outlines the necessary precautions and re-occupancy waiting periods.

Cellulose

Cellulose insulation is manufactured from recycled paper fibre, typically newsprint, treated with borate compounds for fire and pest resistance. It is installed as loose-fill in attic applications or as dense-pack in wall cavities via a blown-in process. Dense-pack cellulose achieves approximately R-3.5 to R-3.8 per inch and, when installed at the correct density, effectively fills the entire cavity — including the irregular gaps around electrical boxes and pipes that batts leave incomplete.

The borate treatment also provides some resistance to mould growth, though cellulose does absorb moisture. If bulk water enters a wall cavity insulated with cellulose, the product can hold moisture for an extended period, increasing the risk of wood decay until it dries out. For this reason, cellulose is more commonly used in attic applications where bulk water intrusion is less likely, or in wall assemblies where a robust drainage plane ensures any water that does enter can drain and dry.

Comparing R-values and climate zone requirements

The table below summarises approximate R-values per inch for the main insulation types used in Canadian residential construction:

  • Fibreglass batt (standard density): R-2.9 to R-3.2 per inch
  • Fibreglass batt (high density): R-3.7 to R-4.0 per inch
  • Mineral wool batt: R-3.7 to R-4.2 per inch
  • Open-cell spray foam: R-3.6 to R-3.8 per inch
  • Closed-cell spray foam: R-6.0 to R-7.0 per inch
  • Dense-pack cellulose: R-3.5 to R-3.8 per inch

Canada's climate zone map, maintained by Natural Resources Canada, divides the country into zones with differing minimum requirements. Southern British Columbia, much of southern Ontario, and parts of Nova Scotia fall in milder zones where a well-installed 2×6 wall with continuous exterior insulation can meet code. The Prairie provinces and northern regions require significantly higher total R-values in wall and attic assemblies.

What to consider beyond R-value

R-value is a laboratory measurement of thermal resistance under idealised conditions. In a real building, total energy performance depends on air sealing quality, thermal bridging through studs and joists, and the location of the vapour control layer relative to the dew point of the wall assembly. A wall with a nominal R-24 assembly that has substantial air leakage will perform considerably worse than a nominally lower-R wall that is well air-sealed.

When comparing insulation options, it is worth considering:

  1. Where the dew point falls within the assembly at design temperatures, and whether the chosen insulation keeps the sheathing warm enough to avoid condensation
  2. Whether a separate air barrier is required or whether the insulation itself provides adequate air resistance
  3. The vapour permeability of the insulation and how it interacts with the intended vapour control strategy
  4. The ability of the assembly to dry in one or both directions if moisture does enter
  5. Long-term thermal performance — some foam products can lose a small portion of their initial R-value as blowing agents diffuse out over years

For most Canadian homeowners undertaking a renovation, the most practical path is to consult a building energy adviser who can model the proposed assembly against local climate data. The EnerGuide home evaluation program through NRCan provides access to registered energy advisers across most provinces.