According to the NBC 2020 and best practices for cold climates like Northern Ontario, where should the primary vapour barrier typically be located within a wall assembly of a residential dwelling?

Question: According to the NBC 2020 and best practices for cold climates like Northern Ontario, where should the primary vapour barrier typically be located within a wall assembly of a residential dwelling?

Answer options:

• On the exterior side of the exterior sheathing.
• Centered within the wall cavity between two layers of insulation. ✅ On the warm-in-winter side of the insulation, typically behind the interior finish.
• Integrated into the exterior air barrier system.

Correct answer: On the warm-in-winter side of the insulation, typically behind the interior finish.

Explanation: In cold climates, the primary vapour barrier should be located on the warm-in-winter side of the insulation, which is typically directly behind the interior finish (e.g., gypsum board). This prevents warm, moist indoor air from migrating into the wall assembly and condensing on colder surfaces.