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

Air movement accounts for more than 98% of all water vapor movement in building cavities. This is primarily due to the principle of diffusion and how air circulates through spaces in a structure. When air moves, it carries moisture along with it, which is critical for understanding how moisture can enter or leave building materials.

The airflow in building cavities can arise from natural convection, mechanical ventilation, or even leakage through gaps and cracks in the building envelope. Because air is so mobile within these cavities, it acts as a primary transport medium for water vapor, which can lead to condensation if not properly managed. Moisture that is transported with air can contribute to issues like mold growth, material degradation, and overall indoor air quality problems, emphasizing the importance of understanding and controlling air movement in building science.

The other factors, while related to the presence of moisture, do not play a significant role in the macro movement of water vapor as air does. This principle is essential for home inspectors to recognize, as it informs how to assess and mitigate moisture-related issues in buildings.