The Airtightness Index is a numerical value used to quantify the level of airtightness or air leakage in a building or building component. It provides a standardized measure that indicates the extent of uncontrolled airflow through the building envelope.
The Airtightness Index is typically derived from airtightness test results, such as a blower door test. During the test, a calibrated fan is used to pressurise or depressurise the building, and the resulting airflow rate is measured. The Airtightness Index is calculated by normalizing the airflow rate with respect to the building size or envelope area.
The Airtightness Index is reported as a volume of air leakage per hour per unit of building envelope area, typically expressed in cubic meters per hour per square meter (m³/h·m²) or cubic feet per minute per square foot (CFM/ft²). It provides a quantitative measure that allows for the comparison of airtightness levels across different buildings or components.
A lower Airtightness Index indicates better airtightness and less air leakage. It signifies that the building or component is more resistant to the uncontrolled movement of air, resulting in improved energy efficiency, reduced heating and cooling loads, and enhanced indoor comfort.