When they built your house, Celotex was used as an economy measure while the plywood was used at the corners for structural strength. If you're going to insulate the walls, the Celotex is sufficient. OSB isn't going to increase your energy savings by much. If you keep the Celotex, be sure the siding is nailed to the studs and not the Celotex.

You may have to supervise that part of the job(the nailing) Unfortunately, most siding installations are incorrectly fastened.

Michael

Thanks for the info Michael.

Scott

Another question... on insulating the walls....when the old siding is removed I will have the Celatex board type material and exsisting R 7 insulation already in the wall. The R 7 is installed with the insulation pushed out towards the outside wall so that there is a ( about 2 or 3 inch or so air gap between the inside wall and the kraft face of the old insulation.

The installer wants to put Tyvack wing material over the house. Is this good enough or should I be doing something better?

Scott

Is it ok to put the new blowen in celulose in that space between the inside wall and the kraft paper from the R7?

Scott

Of course if the wall insulation is in your budget, do it. I will increase the wall value and save you money.

Tyvek is good too. It's a draft barrier and allows venting. Make sure it's taped properly.

Michael