Glossary · Insulation & windows

R-value

Also called: R-values · thermal resistance · R per inch · R-value per inch · effective R-value

How well a material resists heat flow; higher is better, and insulation is rated with it, such as R-20 for walls or R-50 for attics.

What it means

R-value measures resistance to conducted heat. Thicker insulation has a higher R-value, and materials differ in R per inch (see blown-in insulation, spray foam and rigid foam). Real performance is lower when insulation is compressed, has gaps or is bypassed by air leakage or thermal bridging.

Why it matters in an audit

Auditors compare your insulation with recommended or code levels to decide where more will pay off; attics are often the easiest place to add a lot.

Typical numbers

Reference values with their sources. Your energy advisor’s report gives the figure for your own house.

What	Value	Source
NRCan minimum recommended for retrofits, attics	R-40 / R-50 / R-60 / R-60 for heating-degree-day zones A (up to 3,500), B (3,500–5,000), C (5,001–6,500), D (over 6,500)	natural-resources.canada.ca ↗
NRCan minimum recommended for retrofits, walls and basement walls	Walls R-22 / 24 / 27 / 40; basement walls R-19 / 19 / 24 / 25 (zones A / B / C / D)	natural-resources.canada.ca ↗
Quebec government recommendation, attics	R-50 or more	quebec.ca ↗
Code minimum example, new homes, Edmonton (NBC(AE) 2023 prescriptive path)	Attic ceiling RSI 10.43 (R-59) without an HRV or RSI 8.67 (R-49) with one; above-grade walls RSI 3.08 (R-17.5) / 2.97 (R-16.9)	edmonton.ca ↗
Estimating R-value from depth (ENERGY STAR)	Per inch: loose fibreglass ≈ 2.5; rock wool ≈ 2.8; cellulose ≈ 3.7; fibreglass batts ≈ 3.2; vermiculite ≈ 2.7	energystar.gov ↗

In Canada

Canadian codes and labels also give RSI, the metric value; R = RSI × 5.678. NRCan's retrofit recommendations use their own heating-degree-day zones A–D, which are not the same as NBC climate zones.

Sources

Learn more here

Related terms

RSI (metric R-value) The metric version of R-value used in Canada; multiply RSI by 5.678 to get R, so RSI 8.8 is about R-50.
U-factor (U-value) How fast heat passes through a window, door or wall assembly; lower is better, the opposite of R-value.
Blown-in insulation (cellulose, fibreglass) Loose fibres of cellulose, fibreglass or mineral wool blown into attics or wall cavities by machine; fast, and good at filling around obstacles.
Spray foam (open-cell and closed-cell) Liquid foam sprayed in place that expands to insulate and air seal in one step; closed-cell is denser and higher R, open-cell lighter.
Rigid foam (EPS, XPS, polyiso) Stiff insulation boards made of foam plastic, used on foundations, under slabs and as a continuous layer over walls and roofs.
Thermal bridging Heat taking a shortcut through materials that insulate poorly, like wood studs, steel or concrete, running from the warm side to the cold side.
NBC climate zone (Canada) Canada's building code climate zones, set by heating degree days: zone 4 (mildest) to zone 8 (coldest), with zone 7 split into 7A and 7B.

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