What does a vapor barrier help prevent?

A vapor barrier is an essential component in building construction that serves to control the movement of moisture. Specifically, it helps prevent moisture problems by inhibiting the passage of water vapor from one area to another, particularly from the ground or exterior into the interior spaces of a building. This is crucial because excess moisture can lead to various issues such as mold growth, structural damage, and degradation of building materials.

When properly installed, a vapor barrier works effectively to maintain the building's internal environment, reduce humidity levels, and protect against the harmful effects of moisture. In contrast, the other options relate to different aspects of building performance, such as air infiltration, sound reduction, and thermal efficiency, but do not specifically address the primary function of a vapor barrier.