What is more efficient for crawlspace insulation, under the floor or on the walls?
If the crawlspace is vented to the outside, then the floor should be insulated to save energy. Fiberglass is one option, but it should be installed so that it maintains contact with the floor above. Traditionally, crawlspaces have been vented to the outside. Now many building scientists think that the vents bring in more moisture than they remove in some locations, and it is better not to vent the crawlspace but to condition it. Code officials may be hesitant to accept this because they are often not familiar with this.
