What Does Moisture Barrier Do

Also known as a moisture barrier, a floor vapor barrier is typically a sheet of plastic that slows moisture from moving through a wall or subfloor. A moisture barrier is used when installing floors or walls in areas prone to dampness or excess moisture, such as basements, ceilings, or crawl spaces (source).

What is the purpose of a moisture barrier?

A moisture barrier prevents this moisture from evaporating and seeping into the air beneath your home. Moisture barriers are composed of either foil or plastic material that helps prevent moisture from penetrating your crawlspace air.

What happens if I don't use vapor barrier?

If water vapor diffuses or infiltrates into the wall cavity and finds the cool surface, moisture problems can occur. Of course, you can have moisture problems here even without the exterior vapor barrier because of what Bill Rose calls the rule of material wetting.