Choosing an insulation R-value for your region

What does R-value mean, and what is RSI?

R-value measures resistance to heat flow, so a higher number means better insulation. Canada also uses the metric version, RSI. One RSI is about 5.7 in imperial R, so R-20 is roughly RSI 3.5. When you read a product label, a code table or a program rule, check which unit it uses before comparing.

A small example shows why the number matters. Heat flow through a surface is proportional to one divided by its R-value, ignoring framing and air leaks. Going from R-20 to R-40 therefore cuts the heat passing through that area roughly in half. The first extra inches in a poorly insulated attic gain far more than the last ones in a well-insulated one, which is why upgrade order matters, as shown in the insulation priorities guide.

How do climate zones set the target?

Canadian building codes group locations by heating degree days, a measure of how cold a place is and for how long. A warm coastal city and a northern prairie town fall in different zones, and the higher zones require more insulation in the roof, walls and foundation. Provinces adopt or adapt the national model codes on their own schedules, so the numbers differ between provinces and can change between code editions.

For that reason, we do not list a table of required values here. A table copied from one code cycle can be out of date or wrong for your address. The provincial energy ministry or housing authority, your municipal building department and the Government of Canada energy-efficiency pages are the sources to check.

Which parts of the house need the highest values?

Heat rises and roofs see the largest temperature difference, so the attic normally carries the highest recommended R-value, with walls and basements lower. In cold regions the figures widely cited for retrofit attics are well above what many older houses have, often more than double. Walls are limited by framing depth, while basements depend on whether the wall is insulated inside or outside.

• Attic. Largest opportunity: see attic insulation in Canada.
• Basement. Walls and rim joist: see basement insulation.
• Walls. Often limited, with options in exterior wall retrofit.
• Floors over crawl spaces. Covered in crawl space insulation.

Is the code minimum the right target?

Code is a minimum for new construction, not an ideal. Efficient homes such as R-2000 houses and net zero ready designs go beyond it, and the Drake Landing homes were built to R-2000 so that a small solar loop could supply most of the heat. Retrofits are different: the best value is often to reach the recommended level in the cheapest places, such as the attic, before chasing the highest value in every wall.

Nominal R-value is also not the whole story. Gaps, compression, thermal bridging through studs and air leaks reduce the effective result, and an assembly can perform worse than the number on the bag. Good installation and air sealing matter as much as thickness.

How do you find the number for your house?

Start with your location and ask the municipal building department which code edition and zone apply. If you plan an upgrade through an incentive program, read its rules, since some set their own targets. An energy adviser can measure what you have now and recommend levels as part of a home energy audit. The EnerGuide rating is another way to compare your house against others once the work is done.

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