What is the purpose of a vapor barrier in construction?

A vapor barrier serves a critical function in construction by preventing moisture from passing through walls or floors. This is especially important in areas where high humidity or moisture is present, such as basements or bathrooms. By inhibiting the transfer of moisture, vapor barriers help to avoid potential issues like mold growth, wood rot, and damage to insulation which can arise from excessive moisture accumulation.

In contrast, while enhancing aesthetics is an important consideration in construction, it is not the primary function of a vapor barrier. Structural support is provided by other elements of a building's framework and does not relate to moisture control. Allowing ventilation is also contrary to the purpose of a vapor barrier, as its role is to keep moisture in check, rather than to facilitate airflow which could introduce more moisture into the space. Thus, the primary and essential purpose of a vapor barrier is indeed to prevent moisture from passing through critical building components.