Conversion Formula
R-value = RSI x 5.678 (ft²·°F·hr/BTU = m²·K/W x 5.678)
U-value (W/m²·K) = 1 / RSI
U-factor (BTU/hr·ft²·°F) = 1 / R-value
R-Value to RSI Quick Reference
| R-Value (Imperial) | RSI (m²·K/W) | U-Value (W/m²·K) | Common Application |
|---|---|---|---|
| R-4 | 0.70 | 1.42 | 1 in rigid foam (EPS) |
| R-5 | 0.88 | 1.14 | 1 in XPS rigid foam |
| R-8 | 1.41 | 0.71 | 2 in EPS or closed-cell spray foam |
| R-10 | 1.76 | 0.57 | 2 in XPS or 1.5 in closed-cell |
| R-12 | 2.11 | 0.47 | 2x4 wall batt (fiberglass) |
| R-14 | 2.47 | 0.41 | 2x4 wall batt (mineral wool) |
| R-19 | 3.35 | 0.30 | 2x6 wall batt (fiberglass) |
| R-20 | 3.52 | 0.28 | 2x6 wall batt (mineral wool) |
| R-22 | 3.87 | 0.26 | 2x6 wall with exterior foam |
| R-24 | 4.23 | 0.24 | NBC min. wall (most climate zones) |
| R-28 | 4.93 | 0.20 | 2x8 wall or advanced framing wall |
| R-30 | 5.28 | 0.19 | Vaulted ceiling / floor above garage |
| R-40 | 7.04 | 0.14 | Attic -- NBC min. (zones 5-6) |
| R-49 | 8.63 | 0.12 | Attic -- NBC min. (zones 7-8) |
| R-60 | 10.57 | 0.09 | Attic -- high-performance / Passive House |
| R-80 | 14.09 | 0.07 | Attic -- net-zero ready target |
Canadian NBC Minimum Insulation Requirements (Part 9)
| Assembly | Climate Zone 4 | Climate Zone 5-6 | Climate Zone 7-8 | Notes |
|---|---|---|---|---|
| Attic / ceiling | RSI 6.97 (R-40) | RSI 7.04 (R-40) | RSI 8.67 (R-49) | Above conditioned space |
| Above-grade walls | RSI 2.97 (R-17) | RSI 3.52 (R-20) | RSI 4.23 (R-24) | Clear-field effective RSI |
| Below-grade walls | RSI 1.76 (R-10) | RSI 2.11 (R-12) | RSI 2.99 (R-17) | Foundation wall insulation |
| Slab-on-grade (perimeter) | RSI 1.76 (R-10) | RSI 1.76 (R-10) | RSI 2.11 (R-12) | Edge insulation minimum |
| Exposed floor | RSI 3.52 (R-20) | RSI 3.52 (R-20) | RSI 4.91 (R-28) | Floor above unheated garage / crawl |
Values are minimums from NBC 2020 Part 9. Provincial codes and local AHJs may be stricter. Zone 4 covers mild Canadian climates (coastal BC); zones 7-8 cover northern regions including most of the Prairies, northern Ontario, and Quebec. Effective assembly RSI accounts for thermal bridging through framing.
Common Insulation Materials -- R-Value per Inch
| Material | R/inch (Imperial) | RSI/25mm (metric) | Notes |
|---|---|---|---|
| Fiberglass batt (standard) | R-2.9 - 3.8 | 0.51 - 0.67 | R-12 in 2x4, R-19 in 2x6 |
| Mineral wool / Rockwool batt | R-3.0 - 4.2 | 0.53 - 0.74 | Better fire resistance; R-14 in 2x4 |
| Blown fiberglass (loose fill) | R-2.2 - 2.9 | 0.39 - 0.51 | Settles over time; common in attics |
| Blown cellulose (loose fill) | R-3.1 - 3.7 | 0.55 - 0.65 | Recycled content; good for attic |
| EPS rigid foam (Type II) | R-3.6 - 4.0 | 0.63 - 0.70 | Common exterior sheathing board |
| XPS rigid foam (extruded) | R-5.0 | 0.88 | Best for below-grade applications |
| Polyiso rigid foam | R-5.5 - 6.5 | 0.97 - 1.14 | Best R/inch; degrades in cold |
| Open-cell spray foam | R-3.6 - 3.9 | 0.63 - 0.69 | Air barrier; permeable to vapour |
| Closed-cell spray foam | R-6.0 - 7.0 | 1.06 - 1.23 | Vapour barrier; structural benefit |
| Rigid mineral wool board | R-4.0 - 4.2 | 0.70 - 0.74 | Non-combustible; exterior use |
How to Use the R-Value / RSI Converter
Type an Imperial R-value (like R-20 or R-49) or a metric RSI value. The other field converts instantly. Results also show the corresponding U-value in both unit systems -- useful for window and assembly thermal performance comparisons.
Load common Canadian insulation values with one click: R-19 batt for 2x6 walls, R-49 for cold-climate attics, or RSI values from Canadian building code documents. The context band tells you what NBC climate zone requirement your value meets.
The NBC minimum requirements table covers attics, above-grade walls, below-grade walls, slab edges, and exposed floors for all three Canadian climate zone groupings. Compare your converted value against the minimum for your project location to confirm code compliance.
The insulation materials table shows R-value per inch for all common products. Use it to calculate total assembly R-values: multiply R/inch by insulation thickness, then add all layers. Feed the result back into the converter to get the RSI for Canadian code compliance checking. For window thermal values, use the U-Value Converter.
R-Value and RSI -- Complete Guide for Canadian HVAC
Thermal resistance of building assemblies directly determines heat loss and heating loads. In Canada, insulation packages are sold with Imperial R-values printed on the bag while building codes and engineering specifications use metric RSI. Fluent conversion between these systems is a daily requirement for Canadian HVAC engineers, energy auditors, and building inspectors.
The Conversion Factor: 5.678
The single factor you need is 5.678: RSI = R-value / 5.678, and R-value = RSI x 5.678. This comes from the unit conversion between ft²·°F·hr/BTU and m²·K/W. Memorizing a few key pairs covers most Canadian HVAC work: R-20 = RSI 3.52, R-40 = RSI 7.04, R-49 = RSI 8.63. The conversion applies to individual insulation layers and to whole assembly thermal resistance values equally.
R-Value vs. Assembly RSI
The R-value printed on a batt of insulation is the nominal or labelled value for the insulation material alone. A complete wall assembly has a higher or lower effective RSI depending on the framing fraction. Wood studs at 2x6, 16 inches on centre represent about 15% of the wall area and have much lower thermal resistance than the cavity insulation. This thermal bridging reduces the effective clear-field RSI of the wall by 10-20%. Canadian energy programs and the NBC reference effective assembly RSI, not just the cavity insulation value. For precise assembly calculations, consult RSI assembly guides from NRCan or use an energy modelling tool.
NBC Climate Zones in Canada
The National Building Code divides Canada into climate zones based on heating degree days and other factors. Zone 4 covers mild coastal BC. Zones 5 and 6 cover most of southern Ontario, Quebec, and the southern Prairies. Zones 7 and 8 cover northern Canada including most of the Prairie provinces north of Edmonton, northern Ontario, and Quebec. A Calgary home falls in zone 7 and needs RSI 8.67 (R-49) attic insulation at minimum -- significantly more than the RSI 7.04 (R-40) required in southern Ontario. Use the design temperatures from the Design Temperature Lookup to confirm your project's climate zone.
RSI in Heat Loss Calculations
Heat loss through an assembly is calculated as: Q = A x U x DeltaT, where U = 1/RSI in W/m²K, A is the assembly area in m², and DeltaT is the design temperature difference in Kelvin (or Celsius, since the degree sizes are equal). A 50 m² wall with RSI 3.52 (R-20) and a DeltaT of 40 K (e.g., +20°C inside, -20°C outside) loses 50 x (1/3.52) x 40 = 568 W. That same calculation in Imperial: 538 ft² x (1/20) x 72°F = 1937 BTU/hr. Both equal the same heat loss rate -- 568 W = 1938 BTU/hr. Use the Heat Load Calculator for complete envelope heat loss analysis.
Combining Insulation Layers
When insulation layers are in series (stacked), R-values and RSI values add directly. A 2x6 wall with R-19 batt plus 1-inch XPS exterior insulation (R-5) has a total cavity plus exterior insulation R-value of R-24, or RSI 4.23. Adding two inches of EPS board (R-7.2) instead of the XPS gives R-26.2 (RSI 4.62). Always add RSI values for all layers -- insulation, sheathing, air films, and finishes -- to get the total assembly RSI. For thermal bridging correction, use the parallel-path calculation method described in ASHRAE Fundamentals.
Frequently Asked Questions
Divide the Imperial R-value by 5.678 to get metric RSI. So R-20 = RSI 3.52, R-40 = RSI 7.04, and R-60 = RSI 10.57. To go the other way, multiply RSI by 5.678. A quick mental check: R-values are always about 5 to 6 times larger than the equivalent RSI number. If you have RSI 4.23 on a Canadian code document, that's R-24 in Imperial -- the common minimum wall requirement for many Canadian climate zones.
NBC 2020 Part 9 requires RSI 8.67 (R-49) for attics in climate zones 7 and 8, which covers most of northern Canada and the Prairie provinces. Zones 5 and 6 (southern Ontario, Quebec, southern BC interior) require RSI 7.04 (R-40) minimum. Zone 4 (mild coastal BC) also requires RSI 6.97 (R-40). Many energy efficiency programs like EnerGuide 80 and above push attic insulation well beyond these minimums, often to RSI 10.6 (R-60) or more.
A 2x6 wall with R-19 (RSI 3.35) fiberglass batt has a nominal cavity RSI of 3.35. Adding air films, drywall, sheathing, and cladding brings the total clear-field assembly RSI to roughly 3.6 to 3.8 (R-20 to R-22). Thermal bridging through 2x6 studs at 16 inches on centre reduces the effective assembly RSI to around 3.0 to 3.3. To meet the NBC minimum of RSI 3.52 (R-20) as an effective assembly value, most builders add exterior continuous insulation -- typically 1 to 2 inches of rigid foam board.
R-value and RSI measure exactly the same thing -- thermal resistance -- in different unit systems. Imperial R-value uses ft²·°F·hr/BTU; metric RSI uses m²·K/W. The conversion is RSI = R/5.678. Both indicate how strongly a material resists heat flow: higher values mean better insulation. In Canada, RSI appears in building codes, energy modelling software, and engineering drawings. R-value appears on product packaging, US specifications, and in field conversations. You need to convert between them regularly to confirm code compliance. Use the U-Value Converter to convert the inverse -- thermal conductance -- for windows and assemblies.