I have a customer who has a tar and gravel roof, and a tongue and groove ceiling. I anticipate that the existing insulation is in bad shape and will need to be replaced. She currently has 2" insulation underneath the roof. I told her that she will more than likely need to replace the insulation with 4" ISO insulation, but she says that she wants to re-use the old stuff if the roof is in decent condition. I was under the impression that if you tear off a roof, you have to bring it up to current code which would be R-24. Am I wrong?