Foam Insulation 2.0

how much does a sheet of rigid insulation foam weigh?

I really dont care about anything other than the weight. lbs or kg is fine
either 1/4 inch or 1/2"

How thick?

Can rigid foam insulation be installed in basements underneath or before strapping?

I saw on HGTV, Holmes on homes, they insulated the basement walls and floor. But I noticed that it hadn’t been strapped or studded yet. They glued the panels on and taped all corners and seams. It looked like a good way to seal the area. But how would you strap and drywall that? You cant just glue and screw the strapping to the 2” foam can you?

Glue insulation to the wall, tape/foam the seams. You can then stud the wall in front of the foam, or attach furring strips to the walls (through the foam) with a power actuated gun, then attach the drywall. Foam is a perfectly efficient way to insulate and air seal the basement walls.

Insulation question.?

I own an older home with no insulation. The walls are 4 in deep, but R-15 insulation is only 3 1/2" thick. It does say, on the packaging, it is made for 2X4 construction, but should I put 1/2" Rigid FoamFoam Insulation in addition to the fiberglass batts to make up the difference?

No because if you compress the insulation you will lower the effective R value. The 4" insulation will fluff out to fill the void.

Mike