In regards to water vapor movement through walls, which method allows for significantly more vapor transmission?

The correct choice highlights the significance of air leakage combined with diffusion in facilitating water vapor movement through walls. Air leakage refers to the unintentional flow of air through gaps and cracks in building envelopes. This airflow can carry water vapor with it, vastly increasing the amount of moisture that can enter or exit a building compared to vapor diffusion alone, which is the process where water vapor moves through a material due to concentration gradients.

When air leaks through the walls, it can transport significant amounts of moisture, much more than what could occur purely by diffusion, which is generally a much slower process. Hence, the combination of air leakage and diffusion creates a much larger pathway for water vapor movement. This understanding is crucial in building science and ventilation practices as it helps inform the design and assessment of building envelopes in order to manage moisture effectively and prevent issues such as mold growth or structural damage.