Air leaks are a common problem concerning the building envelope. These air leaks are essentially the result of uncontrolled air movement through the building envelope. Air leaks can cause many problems: Condensation, moisture, mould growth and lower air quality inside the building.
When talking about condensation, it is important to know that warm air can hold more water vapour than cold air. When warm air cools, the percentage of relative humidity increases and can reach a saturation level called the dew point. Then, if the air cools even more, the water vapour surplus which cannot be contained in the air turns into water droplets, thus forming condensation.
Air leaks going through the building envelope are caused by air pressure coming from one or more sources, such as wind pressure, the stack effect, or pressure created by heating, cooling and ventilating mechanical units.