Moisture is something to be managed. A vapor barrier can cut down on earthy smells, mildew, and general humidity.

True vapor barriers should have a permeance rating of ... at least 6 inches above the top of the floor and be secured with tape creating the edges of the imaginary "bathtub." ...

Many homes and additions are built over a crawl space to save time and money. Unlike traditional basements, crawl spaces are often only a few feet tall, built above grade, and many are unfinished ...