I recently purchased and moved into a new home, well it was new 30 years ago. I recently was up in the attic arunning some surrond sound speaker leads and noticed that the insulation was originally what appears to have been 4 inch fiberglass and on top of this there is a layer of blown in insulation of varying thickness. How good is this insulation for keeping heat in in the winter and the "HOT" out in the summer. I live in the Desert South West and it is very hotin the summer. Question is should I consider having this all removed and replaced with something like R30 bat insulation?

Thanks for your comments.