Where must vapor diffusion retarders be installed in colder climates?

In colder climates, vapor diffusion retarders should be installed on the interior face of walls. This placement is crucial because it helps prevent warm, moist air from inside the building from coming into contact with colder surfaces, which can lead to condensation within the wall assembly. When warm air moves toward these cold surfaces, moisture can condense, potentially causing damage to the building materials and promoting mold growth.

By installing the vapor retarder on the interior side, it acts as a barrier that reduces the amount of moisture migrating from the living space into the walls during the colder months. This is essential for maintaining the integrity and longevity of the building structure. Proper installation of vapor diffusion retarders is particularly important in regions with significant temperature differences between indoor and outdoor environments, as it mitigates potential moisture-related issues that could arise from those temperature variances.