What accounts for more than 98% of all water vapor movement in building cavities?

Air movement is responsible for more than 98% of all water vapor movement in building cavities due to the inherent nature of air to carry moisture with it. When air circulates through a space, it can pick up vapor, transporting it from one area to another. This is particularly significant in attics and walls where air leaks or ventilation systems allow for movement of both air and moisture.

In contrast, while liquid water, capillary action, and vapor diffusion play roles in the behavior of moisture in buildings, their contributions to moisture movement are far less significant compared to air movement. Liquid water can contribute to moisture in a space, but it typically does not move through cavities in the same manner as moisture-laden air. Capillary action involves the movement of water through tiny spaces due to surface tension but is limited to specific materials and conditions. Vapor diffusion is the process through which water vapor moves from areas of high concentration to areas of low concentration, but it is generally a slower process compared to the rapid movement facilitated by air. Therefore, air movement is the dominant mechanism governing moisture transport within building cavities.