Mark writes from Springfield, New Jersey: "We have a 1941 Cape with most walls being plaster (thereby limiting access to almost all of the potentially insulate-able areas). The original insulation is a terrible, dried-out, crumbled mess that kind of looks like shredded bits of paper mixed with blown-in insulation. Making matters worse is the fact that the house was re-sided on top of the original asbestos shingles, which are on top of old sheathing which is dried-out and wavy (hello air flow at the sill plate).

"I have taken to using spray foam at the outer edge/base at the house. I've updated the insulation on every wall which I have opened up (redone kitchen and baths, portion of the attic floor above living space). It's terrible and drafty.

"To my current project question: I need to make an odd-sized door (30x64x2") used to access attic space above my garage and am wondering what would be the best insulation to use for this.

"The door will be on a 2nd interior floor wall at the end of the house. The other three walls in the area where the door will open to are all un-insulated exterior walls of the garage, as are the floor and ceiling in that space. I intend to use 2x2 studs to create the interior frame/structure of the door and 1/4" plywood to sandwich the faces of that frame after filling the space inside with compressed R-13. One obvious issue is that the R-value will go to pot, but how much? Enough to prefer using the foam-board type insulation? Is there any reason to insulate those other surfaces in the garage?

"It is already getting extremely hot and cold above the garage. I have also insulated that same wall on the inside of the garage, after cutting out the old plywood. Is it worth putting up plywood again?"

Answer: If you compress R-13 into a 2x2 cavity it will yield an R-8 insulating value. Two inches of FOAMULAR® Insulation will give you an R-10. The plywood is necessary if the insulation you used has exposed Kraft paper. It is a good idea for fire safety and building codes generally require that the paper facing be covered. Exposed unfaced fiberglass insulation does not need to be covered.