There is no harm and the normal practice is to simply add new over the existing insulation.

Thanks. I've been listening to talk radio shows where this has been discussed and they keep saying that the old, compressed material should be removed. Noone ever questioned them on "why"- figured it was just an easy upsale.

There is no reason to remove the old insulation unless it was wet...and then you've got other issues to deal with.

If you decide to remove the old insulation (and I don't know that this needs to be done) call around to insulation companies and you will find one that will "vacuum" out the old stuff. I had this done in 400 sq. ft. where I was doing an extensive remodel. They used 150 ft. of 6" hose, a special centrifugal vacuum and disposable bags that held about 500 lbs. of insulation. Didn't take them long. Cost me $400 and it was the best money I ever spent considering how much easier the plumbing and wiring went.

I don't think the cost for a whole house would be anywhere near $1/sq. ft., but I had a small area and obviously paid for travel time and such. The actually time to vacuum was probably no more than 1 hour.

Thanx. The insulation isn't wet, though it had been. The house was vacant of almost 2 yrs before we purchased, and the roof had leaked. Most of that material was removed when we replaced ceilings, though some if it, I'm sure is still up there.

then check for mold