the south-eastern States) and in some cases in cool climates, especially when air conditioning or cooling (e.g. Warm weather infiltration condensation is often a problem in warm and humid climates (e.g.
Wintertime exfiltration condensation is, however, acknowledged as a common building performance problem in cold climates. Water vapor diffusion, while amenable to simple analysis, is often (but definitely not always) an insignificant source of moisture in modern building envelopes. comfort, health, energy, durability, etc.) problems. Uncontrolled air leakage through the enclosure is therefore often a major cause of performance (e.g. Air flow through the enclosure can also carry, exhaust gases, odours, and sounds through enclosures as well as mold spores and off gassing generated within the enclosure. Wintertime condensation of water vapor in exfiltrating air (or summertime condensation of infiltrating air) within assemblies is one of the two major sources of moisture in the above-grade enclosure (driving rain being the other). A large fraction of a modern, well-insulated building's space conditioning energy load is due to uncontrolled air leakage. That this statement is true for all climates has been a more recently developed awareness. It has long been recognised that the control of air flow is a crucial and intrinsic part of heat and moisture control in modern building enclosures.
