I am a DIY home owner. I am working in my crawl space removing mold and fixing the vapor barrier. In the area I live it is recommend to have 1.5" to 2" thick foam board on the walls. Currently the walls are covered with 3/4" foam board (glued and screwed in place). What is the best way to add more insulation? Add another layer of foam board to existing, remove the current and add new thicker, or add un-faced fiberglass insulation over the current 3/4" foam board?