What is the purpose of using a vapor barrier in a building?

The purpose of using a vapor barrier in a building is primarily to keep moisture from damaging structures. Vapor barriers are materials that reduce the amount of moisture that can pass through walls, ceilings, and floors. They are essential in preventing condensation from forming inside building assemblies, where it can lead to issues such as mold growth, rot, and corrosion of structural elements. When moisture gets trapped in these areas, it can compromise the integrity of the building and lead to costly repairs.

By effectively controlling moisture, vapor barriers help maintain the durability and longevity of building materials and create a healthier indoor environment. While vapor barriers can also impact thermal insulation and air leakage somewhat indirectly, their central function is moisture control, making this the correct understanding regarding their purpose in construction.