Which of the following is NOT a function of a vapor barrier?

A vapor barrier is primarily designed to prevent moisture from infiltrating or migrating into the building envelope, serving an important role in maintaining indoor air quality and preventing damage from moisture. Its main functions include:

• Preventing moisture ingress: This is the most critical function of a vapor barrier, as it helps protect building materials from moisture damage, mold growth, and other moisture-related problems.

• Controlling air leakage: While a vapor barrier's principal role is moisture control, it also contributes to minimizing air leakage. A well-installed vapor barrier helps ensure that air, which can carry moisture, does not escape or enter the building, thus maintaining the integrity of the indoor environment.

The option regarding providing thermal insulation is not correct because while a vapor barrier works with insulation, it does not provide thermal insulation itself. Instead, it complements insulating materials to create a more effective thermal envelope.

Similarly, vapor barriers do not facilitate air exchange. In fact, their installation is intended to restrict airflow to maintain a stable indoor environment. Allowing air exchange through a vapor barrier would defeat its purpose, which is to minimize moisture and protect the building. Thus, identifying that the function of facilitating air exchange does not align with the intended purpose of a vapor barrier makes that option the correct choice.