Where should vapour barriers typically be installed in a wall assembly?

Vapour barriers are critical components in wall assemblies as they help prevent moisture from permeating into the walls where it can lead to mold growth, deterioration of materials, and other moisture-related problems. The correct installation location for vapour barriers is on the warm side of the wall assembly.

This placement is important because in colder climates, warm moist air from inside the building tends to move toward the colder exterior. If the vapour barrier is located on the cold side, any moisture in the warm air can condense when it reaches the colder surface, which leads to moisture accumulation within the wall.

By positioning the vapour barrier on the warm side, it effectively blocks moisture from penetrating into the wall cavity where it might cool off and condense, thus maintaining the integrity of the building materials and ensuring a drier and healthier indoor environment. This practice is essential in climates where significant differences between indoor and outdoor temperatures occur, making it vital for effective moisture management in the building envelope.