1.   Eventually, old insulation has to be replaced.

2.   However, there is no more space left between the joists because the old insulation fills the space up to the top of each beam.

3.   It is fiberglass wrapped in perforated polyethylene to keep the fiberglass from sensitive hands, and to ease its installation on old insulation.

4.   Now you can add the old insulation, and more, unbacked insulation.

5.   The Poly-Wrap is slippery, so it can be moved over old insulation more easily.

6.   Therefore, I suggest taking up the old insulation and installing polyethylene plastic between the joists, right on the ceiling below.

7.   Would asbestos be in old insulation?