What is the purpose of installing a vapor barrier?

The purpose of installing a vapor barrier is primarily to prevent moisture from entering the wall assembly. This is crucial in construction, especially in areas with high humidity or temperature fluctuations, where moisture can migrate through walls due to vapor drive. By installing a vapor barrier on the warm side of the insulation, it helps to keep moisture from condensing within the wall cavity, which can lead to mold growth, wood rot, and degradation of insulation material.

Moisture entering the wall can compromise its structural integrity and thermal performance. Consequently, using a vapor barrier effectively maintains a dry environment within the wall assembly, thereby enhancing the durability and comfort of the building. It is important to note that while insulation and air circulation are important for energy efficiency and comfort, these functions are distinct from the primary role of a vapor barrier. A vapor barrier addresses moisture control rather than thermal resistance or air movement.