What is the main function of a vapor barrier in construction?

The main function of a vapor barrier in construction is to prevent moisture penetration. This is crucial in regulating moisture within building assemblies, ensuring that water vapor from the building's interior does not condense within walls, roofs, or other structural elements. If moisture were to penetrate these areas, it could lead to a variety of problems, including mold growth, wood rot, and structural damage over time.

Vapor barriers are typically installed in areas where moisture is a concern, particularly in climates with high humidity or in environments where there is a significant temperature difference between the interior and exterior of a building. By placing a vapor barrier in the correct position, it effectively blocks the movement of water vapor, thereby protecting the integrity and longevity of the building structure.

While some of the other choices may relate to aspects of building performance, such as energy efficiency or insulation, they do not specifically address the critical role of controlling moisture, which is the primary purpose of a vapor barrier.