Which of the following is a mechanism for moisture entry into buildings that relies on air movement?

• A. Bulk water
• B. Capillary water
• C. Air-transported moisture
• D. Vapour diffusion

Answer: (C)

Moisture entry that relies on air movement is moisture carried by moving air, also known as air-transported moisture. When air flows through gaps, cracks, or around materials, it can pick up water vapor from humid outdoor air or from inside the building and transport it to other locations. This convective transfer means humidity can infiltrate or exfiltrate the building, and moisture can condense on cooler surfaces as the moving air cools or changes humidity. This is distinct from bulk water, which is liquid water intrusion; capillary water, which wicks moisture through porous materials without relying on air flow; and vapor diffusion, which moves moisture through materials due to vapor pressure differences and not the bulk movement of air.