When constructing a new residential basement in Alberta, which strategy would provide the most effective air sealing at the rim joist area to meet current building code expectations while preventing moisture issues?

Question: When constructing a new residential basement in Alberta, which strategy would provide the most effective air sealing at the rim joist area to meet current building code expectations while preventing moisture issues?

Answer options: ✅ Sealing the perimeter of the rim joist with acoustical sealant and covering the entire area with a 6-mil poly vapour barrier taped and sealed.

• Installing unfaced fibreglass batt insulation snugly fitted into the cavity, with no additional sealing.
• Applying closed-cell spray foam directly to the rim joist, sealing all gaps and then covering with 6-mil poly.
• Using rigid insulation board tightly fitted against the rim joist, without sealing the gaps around it.

Correct answer: Sealing the perimeter of the rim joist with acoustical sealant and covering the entire area with a 6-mil poly vapour barrier taped and sealed.

Explanation: Sealing the rim joist with acoustical sealant addresses air leakage, and then a continuous 6-mil poly vapour barrier, properly taped and sealed, prevents moisture migration. This combination provides both air and vapour control, which is the most effective and code-compliant approach when not using spray foam.