Is it wise to put new insulation over old insulation in the attic? I have fiberglass insulation now and would use the same kind from a home supply center. My home was built in 1968. It would be a messy job removing the old insulation and replacing it with new insulation that is why I asked the question of just putting new insulation over the old insulation in the attic.

Leave the old stuff in place and buy unfaced batts, place them perpendicular to the joists and butt tightly together. Do not stuff the batts into the cavity where the joist and roof rafters go into the eaves, eaves must be open to allow air to flow into the attic.

I have just put 10" fiberglass batts on top of 8". The new ones have paper the same as the original. I have since found out the new batts will need to be vented. Am I putting slits or holes ? If so what size cuts/holes per batt?,