my daughter's condo is under insulated! There is about 3 inches of rock wool in the attic (2x6 joists). I want to add insulation. Should I just add 9-12 inches across the joists and leave the 3 inch air gap underneath. I can't find a 3 1/2 inch thick unfaced roll to fill this gap. I really want to cover the wood rafters with insulation. Or should I not even worry about the joists and just lay in 9 1/2 inch batts in between them. I don't know that much about blown in insulation but this seems to be an alternative although I would prefer rolls or batts. The attic is more than full height and appears to be easy to get to the eaves to staple in the foam baffles to do it right. Any suggestions? Thanks in advance.