The Difference Between a Vapor Barrier & Impervious Sheeting

Vapor Barrier

• A vapor barrier, also called a vapor diffusion retarder, is a material that stops or controls water vapor. A vapor barrier can be a solid sheet of foam insulation board, treated plywood, plastic or stainless steel, as well as a coating like paint or a thin sheet or membrane of plastic, aluminum foil or asphalt-coated paper. Any material that water has a difficult time penetrating and can be put over a wet surface to keep another material dry can be called a vapor barrier.

Impervious Sheeting

• Impervious sheeting is a type of vapor barrier. Also called impermeable sheeting, this is a type of thin, flexible material through which water cannot pass. In the construction trade, 6-mil plastic sheeting or rubber membrane is often referred to as impervious sheeting.

Applications

• Vapor barriers, and in particular impervious sheeting, are used anywhere a material needs to be protected from long-term exposure to water and water vapor. They are commonly used under concrete slabs, between concrete slabs and the base of wood-framed walls, and between foundations or masonry walls and interior framing and insulation. Impervious membranes are used under roofing shingles.

Considerations

• According to the U.S. Department of Energy's Energy Savers program, not all climates call for the use of vapor barriers in the same configurations, or even that they be used at all. In cold to moderate climates, vapor barrier should go on the warm-in-winter side of the wall, while in hot, moist climates, the barrier should be on the exterior of the wall. In warm climates that are not humid, no vapor barrier is necessary.