On your show you said that when insulating under a floor, the paper facing should face up against the flooring. Why can’t I install it the other way? Does it make that much of a difference? -Kim
Regardless of whether fiberglass insulation is installed in a wall, attic, or crawlspace; the paper facing should always face toward the inside of the home. That’s because the paper contains a layer of asphalt adhesive which prevents water vapor from passing through it.
If the insulation is installed with the paper vapor barrier facing away from the heated part of the home, moisture from humid inside air can condense and become trapped in the insulation during cold winter months. This can lead to rot and mold.