What R-value is required for above-grade exterior walls in NBC Climate Zone 7?

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## R-Value Requirements for Above-Grade Exterior Walls in NBC Climate Zone 7

The National Building Code of Canada 2020 does not prescribe a single fixed R-value for above-grade walls in Climate Zone 7; instead, it uses an energy conservation points system with minimum effective RSI values, while Ontario applies stricter supplementary requirements through its own adopted version of ASHRAE 90.1.

### National Building Code 2020 (Prescriptive/Points System)

Under the NBC 2020 energy conservation points framework, above-grade walls in Climate Zones 7A (5,000 to 5,999 Celsius degree-days) and 7B (6,000 to 6,999 Celsius degree-days) must achieve minimum effective RSI values to earn the corresponding points. For example, a minimum effective RSI of 3.08 (m²·K)/W (approximately R-17.5) earns 2.1 points in Zone 7A and 0 points in Zone 7B, while a minimum effective RSI of 3.69 (m²·K)/W (approximately R-20.9) earns 6.7 points in Zone 7A and 5.4 points in Zone 7B . The maximum listed effective RSI of 5.45 (m²·K)/W (approximately R-30.9) earns 13.6 points in Zone 7A and 13.1 points in Zone 7B . The designer selects the RSI target that, when combined with other measures, achieves the total points required for compliance.

### Ontario (OBC 2024 and Supplementary Standard SB-10)

For nonresidential and residential buildings governed by Ontario's SB-10 (which supersedes ASHRAE 90.1 Table 5.5-7 for Climate Zone 7), the minimum insulation requirements for above-grade walls are more specific by assembly type:

- **Mass walls:** minimum R-20 ci (RSI 3.5 ci), maximum U-0.261 W/(m²·K)
- **Metal building walls:** minimum R-13 + R-19 ci, maximum U-0.225 W/(m²·K)
- **Steel-framed walls (nonresidential):** minimum R-13 + R-15 ci, maximum U-0.250 W/(m²·K)
- **Wood-framed and other:** minimum R-13 + R-10 ci, maximum U-0.261 W/(m²·K)

Ontario also mandates that where electric space heating is used, the building envelope shall comply with Table SB 5.5-7-2017 regardless of climate zone .

### Alberta (NBC Alberta Edition 2023)

Alberta follows the same NBC points-based framework as the national code, using Table 9.36.8.5 for above-grade walls with effective RSI thresholds and corresponding energy conservation points across Zones 7A and 7B .

### Key Takeaway

The minimum wall R-value in NBC Climate Zone 7 depends on the assembly type and compliance path chosen. Ontario's SB-10 imposes the most prescriptive requirements, ranging from R-13 + R-10 ci for wood-framed walls up to R-13 + R-19 ci for metal building walls. Always confirm which provincial edition and supplementary standards apply to the specific project jurisdiction.

What R-value is required for above-grade exterior walls in NBC Climate Zone 7?

R-Value Requirements for Above-Grade Exterior Walls in NBC Climate Zone 7

National Building Code 2020 (Prescriptive/Points System)

Ontario (OBC 2024 and Supplementary Standard SB-10)

Sources cited