I have an unfinished basement with fiberglass insulation between the joists. The insulation is old, a bit loose in many places and sags. It was suggested that I could use bubble foil insulation stapled to the joists to provide a cleaner more attractive look. This would help when trying to sell the house for sure. My question is whether I can do this right below the existing fiberglass insulation or would I need to remove the old stuff for any unknown reasons.