We have a crawlspace attic in our home that covers the entire top of the house. The whole floor and walls slanting to the roof are all insulated. Part of the floor (roughly a quarter of it) is covered in plywood, allowing us to store stuff on top of it. I'm considering covering the rest of the floor with plywood (need more storage space), but I thought I heard that it's more efficient to leave the majority of the insulation open (not covered by plywood). Is this true? Any suggestions?