Why SHOULDN’T I use a vapor barrier?

There is no reason not to use a vapor barrier in your crawl space. 

Some people think they’re in the clear if they have a concrete crawl space floor rather than a dirt one. However, moisture can still penetrate porous concrete and intrude through open vents. 

A vapor barrier coupled with vent covers and other encapsulation solutions will keep your crawl space dry, healthy, and functional.