In cold-winter climates, where are vapor barriers typically installed in wall assemblies?

In cold-winter climates, vapor barriers are typically installed on the interior side of wall assemblies. This is crucial because the warm air inside the home contains more moisture than the cold air outside. When warm, moist air comes into contact with the cold wall assembly, it can condense within the wall if there is no barrier to prevent this moisture from moving inward.

By placing the vapor barrier on the interior side, it helps to keep moisture from penetrating into the wall structure where it can lead to issues like mold growth or degradation of building materials. This placement effectively protects the insulation and structural components from moisture damage, which is essential for maintaining the integrity of the building envelope in cold climates.

Other locations for vapor barriers, such as the exterior side or within the middle layer, would not effectively prevent indoor moisture from penetrating the wall assembly, leading to potentially serious long-term issues. A top layer arrangement doesn't align with the common practices in wall assembly design focused on thermal efficiency and moisture control.