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.

Batt insulation is the poorest there is because it allows infiltration of air. The convection currents within it rob you of energy dollars.

That is why the cellulose was blown over it. This is far better for insulating than fibreglas batts. If you want to improve on it, have more cellulose blown in.

Excellence is its own reward!