What does 'air leakage' refer to in the context of building performance?

Air leakage in the context of building performance refers specifically to the uncontrolled movement of air through various openings, such as leaks, holes, and cracks in the building envelope. This uncontrolled airflow can significantly impact a building's energy efficiency, comfort, and overall performance.

When air leaks through unintended openings, it can lead to a range of issues, including increased energy costs due to heating and cooling losses, discomfort for occupants, and potential moisture problems that can lead to mold and structural damage. Understanding and managing air leakage is crucial for optimizing building performance, as it directly affects how a building interacts with its environment.

While planned ventilation openings, evaporation of moisture, and movement of air caused by temperature differences are all relevant to building science, they do not specifically encapsulate the concept of air leakage. Planned ventilation openings are intentional and controlled, evaporation is related to moisture control rather than air movement directly, and temperature-induced air movement refers to stratification and natural convection rather than leaks through building materials. Thus, the correct answer accurately captures the essence of air leakage as an uncontrolled phenomenon that negatively impacts building performance.