What is vapor diffusion?

Vapor diffusion refers to the process by which moisture in the form of water vapor moves through materials, and this occurs primarily due to differences in pressure and temperature. This phenomenon is significant in building science, particularly in relation to moisture management and the overall performance of a building envelope.

When there are variations in vapor pressure (resulting from temperature differences), water vapor will naturally move from areas of higher vapor pressure to areas of lower vapor pressure. This process can influence mold growth, structural integrity, and indoor air quality, making it essential for home inspectors to understand and assess in their evaluations.

The other options address different but related concepts: movement of liquid water through cracks focuses on liquid infiltration, flow of air through ducts involves forced air systems and ventilation, and the process of condensation relates to the transformation of vapor into liquid under certain temperature conditions. While all these elements interact within a building's moisture dynamics, they do not describe vapor diffusion specifically.