Occupants of buildings, appliances, and plumbing equipment generate moisture that is carried in the air as a vapor. As moisture vapor moves from a warmer interior through construction materials to a cooler surface, the moisture may condense as water, which may damage the building. It is for this reason that vapor retarders, which retard the flow of moisture through construction materials, are installed in buildings. By locating vapor retarders as close as possible to the warm-in-winter (heated interior) surface of the building, the moisture vapor flow is restricted before it has a chance to condense to water. (See Figure 4.)