What is meant by 'air permeance'?

Air permeance refers specifically to the measurement of air flow through materials, particularly those used in building envelopes. It quantifies how much air can pass through a material, usually expressed in terms of cubic feet per minute per square foot (cfm/ft²) at a given pressure differential. This is a crucial characteristic of air barrier materials since an effective air barrier will minimize unwanted air flow through the building envelope, thereby improving energy efficiency and indoor air quality.

Understanding air permeance is essential for professionals involved in building design and construction, as it directly impacts the performance of air barriers, energy consumption, and overall building durability. High air permeance indicates a material may allow too much air flow, which can lead to energy loss and potential moisture issues, while low air permeance signifies an effective barrier against air infiltration. Hence, recognizing and measuring air permeance helps in selecting materials that contribute to building performance and compliance with energy codes.