In terms of moisture transport, which is greater?

Air leakage is the correct answer because it plays a significant role in the transport of moisture within a building envelope. When air leaks into or out of a building, it carries water vapor along with it. This movement can significantly increase the total amount of moisture transported compared to other processes such as vapor diffusion, which occurs through materials at a molecular level and is generally slower, and liquid water movement, which is limited to direct contact with water sources.

Air leakage occurs rapidly and can encompass a large volume of air in a short time, which combined with humidity levels, can result in substantial moisture transfer. This is particularly relevant in scenarios where there are temperature differences between indoor and outdoor air, creating conditions where moisture can enter or escape more effectively.

While phenomena like condensation can lead to localized moisture issues, they do not actively transport moisture in the same volume as air leakage. Therefore, understanding the dynamics of air leakage is critical in assessing and managing moisture levels in building performance, especially in airtightness testing and strategies designed to mitigate moisture-related issues.