1. There is a difference between vapor retarders, vapor barriers, and waterproofing materials and when each should be used under a concrete slab on grade.
2. Vapor retarders are used to slow the transmission of water vapor from the soil into the building through the slab, while vapor barriers completely block vapor transmission.
3. Proper installation of a vapor retarder under the slab is important to prevent moisture-related problems with flooring materials and to restrict soil gases from entering the building.