Replies

1. Expert Member
   Zephyr7|Mar 05, 2020 12:25pm|#1

   Depending on what you’re using for siding, you’ll probably want to put something with some structure to it in the opening like plywood or OSB. There is no reason not to also put some polyiso in though, it’s just that polyiso alone won’t provide any strength to the wall or anything to fasten siding to.

   Bill

2. Expert Member
   Malcolm Taylor|Mar 05, 2020 12:40pm|#2

   renogrant,

   Can you clarify why you want to include the foam there? Sheathing is usually confined to the exterior of walls. The rough opening is uncovered dimension lumber.

1. 
   renogrant|Mar 05, 2020 12:54pm|#3

   Thanks. The poly would act as the sheathing on the exterior of the wall. The wood siding would be nailed through the poly to the wood structure. I believe the value in using the foam is that it would limit thermal bridging and provide greater r value.

3. 
   renogrant|Mar 05, 2020 12:55pm|#4

   Thanks. The poly would act as the sheathing on the exterior of the wall. The wood siding would be nailed through the poly to the wood structure. I believe the value in using the foam is that it would limit thermal bridging and provide greater r value.

1. Expert Member
   Zephyr7|Mar 05, 2020 01:59pm|#5

   Then that would work. In my own home, I have T111 siding over 1/2” polyiso, with the T111 nailed through the polyiso directly into the framing.

   BTW, using “poly” when you mean “polyiso” will cause a lot of confusion with construction people. “Poly” usually means “polyethylene”, which is commonly used as a vapor barrier. “Polyiso” means “polyisocyanurate”, which is a rigid foam insulation product. A very big difference! :-)

   Bill