Which of the following is not a function of vapor retarders?

The correct answer is that allowing air movement is not a function of vapor retarders. Vapor retarders, which can come in the form of films or membranes, are designed to limit the flow of water vapor from one area to another within a building. Their primary role is to reduce the transfer of moisture, which helps to prevent condensation that can lead to mold or structural damage.

Vapor retarders effectively reduce the flow of water vapor, acting as a barrier that minimizes humidity levels within conditioned spaces. While preventing moisture from evaporating can occur in specific contexts (such as maintaining humidity levels in some environments), it is not their dominant purpose. The primary focus lies in restricting the passage of moisture, rather than facilitating air movement. This distinction is crucial as it highlights the specific application and effectiveness of vapor retarders in managing moisture within building assemblies.