Envelope leakage, also known as building envelope leakage or air leakage, refers to the uncontrolled movement of air through the building envelope. It occurs when outdoor air infiltrates into the building or conditioned indoor air escapes to the outside through gaps, cracks, joints, or other openings in the building’s exterior.
Envelope leakage is a common issue that can have significant impacts on energy efficiency, indoor comfort, and indoor air quality. It can result in energy losses, increased heating and cooling demands, drafts, temperature variations, and the infiltration of outdoor pollutants, allergens, and moisture.
The building envelope consists of various components such as walls, roofs, floors, windows, and doors, which together form the barrier between the interior and exterior environments. However, these components may have inherent or developed weaknesses that allow air to pass through, leading to envelope leakage.
Addressing envelope leakage involves implementing air sealing measures to minimize or eliminate the uncontrolled air movement. This includes sealing gaps, cracks, joints, and penetrations using air barrier materials, tapes, sealants, gaskets, and other appropriate techniques.
Airtightness testing, such as blower door tests, is often conducted to assess and quantify envelope leakage. These tests involve pressurising or depressurising the building and measuring the airflow rate required to maintain a specific pressure difference. The results provide valuable information about the overall airtightness of the building envelope and help identify areas of concern that require attention.
By reducing envelope leakage, building owners and professionals can improve energy efficiency, minimize heating and cooling loads, enhance indoor comfort by reducing drafts and temperature variations, and ensure better indoor air quality by controlling the infiltration of outdoor pollutants, allergens, and moisture.