What Is Air Transport of Moisture?

Air transport of moisture refers to the movement of water vapor carried by moving air through gaps, cracks, and penetrations in a roof assembly. This mechanism is one of the most significant contributors to moisture accumulation in roofing systems.

Definition of Air Transport of Moisture

Within the ROOFNOW™ Knowledge Center (RNKC), air transport of moisture is defined as the bulk movement of moisture-laden air driven by pressure differences within a building envelope.

How Air Transport Occurs

• Stack effect from warm air rising
• Wind-driven pressure differences
• Mechanical systems creating pressure imbalance

Why Air Transport Is More Impactful Than Diffusion

RNKC explains that air leakage can move significantly more moisture than vapor diffusion over the same time period, making air sealing a critical component of moisture control.

Learn more at the ROOFNOW™ Knowledge Center.