2×6 stud wall + 1/2″OSB+1.5″ Foam: WRB needed and where?
ketchgould
| Posted in General Discussion on
I am building my home in Northern Wisconsin. The walls are 2×6 advanced framing and moving outward to 1/2″ OSB and then 1.5″ of foam board and then vertical standing seam steel siding.
Would you use the pink XPS (R 7.5) $25 per sheet foam over the OSB or laminated EPS (R6) $19 per sheet?
Also, is WRB necessary if I tape the foam seams?
I am going to buck the windows with 2x8s that are flush with the 1.5″ foam. Can I simply tape the window opening directly to the XPS or laminated EPS?
Replies
You can do the WRB either on the sheathing or the foam. If your windows are flush with the foam, it may be easier to do it on the outside, otherwise you need to detail your air barrier to also include the 2x8 buck.
Second - you need some insulation on that 2x8 buck if possible, either by making it smaller and adding foam on the outside, so a 2x6 with 2 inches of foam attached to the outside, or using a thermalbuck type product where the whole thing is insulated. As is , the 2x8 is a buck is a thermal break.
I would love to use a 2x6 buck and have the 1.5" foam cover the 2x6. I would have to attach the window through the an inch and a half of foam, is that reasonable? Use a 2 1/2" screw?
Thanks
You would definitely want your screws to reach into wood framing, not just to the foam. So 2 1/2" should be good.
They do have pre-fabricated insulated bucks you can look into, but not sure about the pricing difference and all of that.
Sounds like you're in the thick of it with your new construction plans. Insulating headers can be tricky, but it's great that you're thinking about thermal bridging. It seems like your architect's solution with the 1" rigid foam on the inside might help, but your contractor's suggestion of 2" foam on the outside could be even better. Keeping wood warm can indeed help prevent rot, so insulation on the outside might be a good call. It's all about finding the right balance for your project. Good luck with the permits, and I hope everything goes smoothly for you!