Wall Section Detail – Climate Zone 6
Hi all . . . I’m back with a follow up question on wall section detail for new construction in Climate Zone 6 (northern Vermont). Here is my wall section from inside to out:
1/2″ drywall with latex paint
2×6 studs
Rockwool batts OR dense packed cellulose insulation (contractor’s choice)
Flash coat of spray foam on interior face of exterior sheathing (flash & batt)
1/2 CDX plywood sheathing
WRB membrane on exterior face of sheathing – taped joints and corners
2″ rigid foam insulation (instead of R9 (2″) Zip Sheathing)
1x vertical strapping (rainscreen)
1x horizontal strapping (rainscreen)
vertical board and batten siding (Hardi or equal tbd)
3 questions:
Do I need a air or vapor barrier on inside face of studs (next to drywall)?
Do I need a membrane or protection board on outside face of rigid foam insulation? Or is the rigid foam “exposed” to the rain screen drainage channel?
Any other suggestions/thoughts?
I have been told that the R9 Zip Sheathing (2″ rigid) is difficult to secure to the stud framing given the +2″ separation between the sheathing face and the stud resulting in a “loose” connection. This is why I am proposing 1/2″ sheathing on the studs and the 2″ rigid mounted on outside. But I am concerned that the rigid will deteriorate over time even though it is behind the rainscreen system; thus the question about protection board on the outside face of foam. Seems duplicative and expensive to use the 1/2 cdx sheathing on the studs and THEN mount the Zip R9 panels to that, so looking for the best way to detail the continuous 2″ rigid on the exterior.
Any/all thoughts welcome and thank you in advance!
Blake
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Replies
Zip R sheathing ultimately has less shear capability, hence why it needs a closer nailing pattern. I’m building my home right now and couldn’t get zip r6 at the time I purchased sheathing. I am attaching r5 to the outside now and I regret that I went this way. If your structural engineer determines the zip r9 meets all requirements I would go that route.
Thanks for your quick reply. Can you tell me why you regret mounting the rigid to the outside of the sheathing?
I like your wall a lot!
Why do you want spray foam?
Have you considered the regular Zip sheeting?
Consider two one inch layers with staggered seams instead of the single two inch layer.
I see spray foam in new construction plans as a red flag for poor planning by someone looking for an easy fix with little regard for the cost.
Walta
i haven't installed the r9 sheathing on a stud wall but could see how it would be fussy. that said, the many layers of your wall system are fussier IMO. With the zip, you don't need that weather barrier since it's built in and the layer of "closed" cell spray foam inside the stud cavity at the exterior side will give you your vapor barrier.
I would simply bump up the exterior rigid to R11.25 and call it a day.
You can get there if you go with 2" or so of polyiso, no need for any interior spray foam or a warm side vapor retarder. You do want to tape the seams of the CDX as your main air barrier.
If you want to save cost, you can build with Zip R6 but this now needs a warm side vapor retarder (faced batts or variable perm membrane).
Lot of codes allow for only drywall to brace walls if you are not in high wind or seismic area, so I would not loose too much sleep on slightly "loose" connection. You can also always put some let in bracing at the corners of the house.