What is the best foam board insulation under drywall?

Wesley Pracht
Updated: Sept. 4, 2020

I live in Climate Zone 6 in a low humidity, cold, and snowy environment. Heating only no cooling. Currently have T1-11 siding, tar paper, R13 FB insulation, and the interior finish is 1/4 plywood panels.

The siding is in OK shape but I really want the plywood panel interior gone and replaced with drywall. My idea is to tear out the plywood and remove the old FB insulation. I would like to replace with R15 Rockwool and about 1" of foam board insulation attached to the stud and seams taped. Then I would set 1/2" drywall on top of the foam and attached with long screws.

Does this sound like a good plan? Would anyone suggest against using Polyiso insulation as it does not do good in cold environments? Please let me know your thoughts

Responses (3)

H Vargas
H Vargas 1 year ago
Mike Reynolds 1 year ago

Hi Hugo,

I would not worry at all about it compressing while attaching it to a wall, it behaves pretty much the same as EPS rigid foam in that cirmcumstance. Any compression would be right where the screws are, it would be insignificant, and once it's attached to a wall it would not compress any further.