A carpenter is installing new windows in a commercial building in Manitoba. To minimize thermal bridging around the window opening, which detailing strategy is most effective?

Question: A carpenter is installing new windows in a commercial building in Manitoba. To minimize thermal bridging around the window opening, which detailing strategy is most effective?

Answer options:

• Simply caulking the perimeter of the existing rough opening before window installation. ✅ Filling the rough opening cavity with low-expansion spray foam and ensuring continuous insulation laps over the frame.
• Leaving a 10 mm gap around the entire window for air circulation.
• Using only standard fibreglass batt insulation to fill the space between the window frame and the rough opening.

Correct answer: Filling the rough opening cavity with low-expansion spray foam and ensuring continuous insulation laps over the frame.

Explanation: Low-expansion spray foam provides excellent air sealing and insulation around the window frame, minimizing thermal bridging. Critically, ensuring continuous insulation laps over the frame further extends the thermal envelope, significantly reducing heat bypass around the window assembly.