It comes down to one question. Is your crawl space vented to the outside, or sealed up? If it’s vented, with those little screened openings in the foundation, the insulation goes up in the floor joists, under the rooms you live in. If it’s sealed, or you’re about to seal it, the insulation moves to the crawl space walls, and the ground gets covered with a vapor barrier. The U.S. Department of Energy lays it…