How does mold get its start in buildings? Consultant Ralph LaMacchia said it has a lot to do with temperature changes, even in areas where the weather is fairly consistent.
"When the temperature drops, it crosses the dew point. At the dew point, moisture condenses. This is calculated by architects and engineers on what is called a Psychrometric Chart," he explained. "It is easier to manage in the north where there is warm, moist air on the inside and cold on the outside. In warm areas the outside high temp and high humidity begin to migrate through the wall and become colder. Therefore, you will once again hit dew point. Even if you do not have a good vapor barrier, it will condense on the back of the wall covering, or it will find a place, such as metal studs. The metal stud is cold and hot; wood is better as it does not provide the thermal bridge that metal studs do, in which case, the moisture will find some other place to gather. The principal is the same wherever you may be."