In what part of a wall assembly is a vapor barrier usually located?

A vapor barrier is typically installed on the interior side of a wall assembly. Its primary purpose is to prevent moisture from the indoor environment from penetrating into the wall structure, which can lead to condensation and subsequent issues such as mold growth and wood rot. By placing the vapor barrier on the interior side, it effectively protects the insulation and other structural components of the wall from moisture that could compromise their integrity.

In colder climates, this is particularly important as warm, moist air from the interior can come into contact with cooler surfaces, causing moisture to condense. Therefore, positioning the vapor barrier on the interior side provides a critical line of defense against these potential moisture problems.

Furthermore, the location of the vapor barrier is influenced by the climate and the moisture control strategy of the building. In warmer climates, the placement may vary, but generally, the principle of reducing moisture flow into the wall assembly remains consistent.