Unintentional air leakage (Infiltration) occurs through air leakage points in the building envelope. The three causes of pressure difference - wind, stack effect and combustion/ventilation effect act together to drive air in, and out of the building through the air leakage points. This uncontrolled air leakage can account for up to 10% to 40% of the annual heating or cooling energy requirements in conventional homes.
Unintentional air leakage (Exfiltration) outward through the building envelope is the major cause of water vapour movement into exterior walls and ceilings. Water vapour transported through air leakage can be up to 100 times that of vapour diffusion through the building envelope.
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