Crawlspaces should be insulated on their perimeters — they should not be insulated between floors. ... Crawlspace walls should be insulated with non-water sensitive insulation that prevents interior air from contacting cold basement surfaces—the concrete structural elements and the rim joist framing.

What is the best way to insulate a crawl space with a dirt floor?

Dirt floors allow moist air and water to enter the crawl space. You need to hold back this moisture. And the best way of doing this is by encapsulating the crawl space. It involves laying down a 20-mil polyethylene plastic vapor barrier over the crawl space floor and walls.

Should I insulate under my floor?

Floors above cold spaces—like vented crawl spaces and unheated garages—should be insulated, but don't forget about under the flooring. This will help ensure maximum energy efficiency for your home. According to the U.S. Department of Energy, it's ideal to insulate: Slab floors built directly on the ground.