MODERN NORTH AMERICAN (NA) BUILDING ENCLOsures are highly insulated and airtight. Most NA houses and buildings use mechanical ventilation. The use of air conditioning is becoming more and more prevalent. These and many other changes [1] have reduced the drying potential of walls and required that consideration of moisture in building enclosures (BE) becomes a more important component in the design process. Therefore, the objectives of a designer or builder with respect to moisture control are: 1. To ensure the adequate performance during the service life. 2. To ensure good indoor environment by avoiding mold growth inside or on BE surfaces. 3. To ensure economic use of energy and materials.