Illustration Source: Summerhill

9.25.4.3.(1) Products installed to function as the vapour barrier shall protect the warm side of wall, ceiling and floor assemblies.

9.25.4.3.(2) Where different products are used for the vapour barrier and the insulation, the vapour barrier shall be installed sufficiently close to the warm side of the insulation to prevent condensation at design conditions.

9.25.4.3.(3) Where the same product is used for the vapour barrier and the insulation, the product shall be installed sufficiently close to the warm side of the assembly to prevent condensation at design conditions.