Where is the vapor barrier typically located in an exterior wall?

The vapor barrier is typically located on the warm side of the house in an exterior wall assembly. This is crucial because its primary function is to prevent moisture from the warm inside air from migrating into the wall cavity, which can lead to condensation, mold growth, and potential structural damage. By placing the vapor barrier on the warm side, it effectively inhibits the warm, moist air from penetrating into cooler areas of the wall where it may condense.

Positioning the vapor barrier in this manner balances the thermal environment of the wall system, ensuring that any moisture that does accumulate is managed effectively without compromising the insulation or the structural integrity of the building envelope. This practice is particularly important in climates where there is a significant difference between indoor and outdoor temperatures, as the warm air from inside can carry moisture that can become problematic if allowed to enter the wall assembly.