Double wall exterior sheathing
I am designing a near zero energy home in climate zone 5 and working out the details for a double wall system.
There is a lot of talk about what kind of sheathing to use or not use due to the fact that the sheathing will be very cold. As I understand what I have read so far, it is recommended NOT to use OSB or foam but OK to use DensShield Gold, structural fiber board or plywood in Zone 5.
I have not seen anything about Huber’s Zip system in this application. I realize it is an OSB product, but its a lot less permeable than regular OSB and seems to be in a class unto itself. I am thinking that if it is suitable it may be less expensive than plywood and also serve as the WRB.
My proposed wall stack from outside to inside is as follows
vinyl siding (mfrd stone in some areas)
drainage plane
WRB
1/2″ plywood
2 x 4 24″ o.c. double wall 12″ thick with dry-packed cellulose
drywall and paint
What are your thoughts on using 7/16 Zip sheathing system (no foam) instead of plywood and WRB?
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Replies
Terry,
Zip System sheathing hasn't been on the market for long enough for builders to have a good handle on its long-term durability. Like you, I suspect that it can handle repeated cycles of wetting and drying better than ordinary OSB -- but I'm not sure.
Zip System sheathing reportedly has a vapor permeance of 2 to 3 perms. If you want a more permeable sheathing, choose board sheathing, fiberboard, or DensGlass.
Manufactured stone is a very risky cladding to install over OSB. I would be very wary of installing it on the wall you describe, because it has been associated with so many wet-wall problems.
Thanks Martin, I didn't know if anyone has had experience with Zip system in this application or not.
I have used Advantech sub-flooring for as long as it has been on the market and its ability to withstand mass water is remarkable. I don't know if the formulation is the same for the sheathing product.
Nevertheless, will probably go with DenShield or plywood and a separate WRB on this one.
One other option is simple pine boards, if you are somewhere that you can buy locally milled rough sawn pine cheaply. More permeable than plywood, especially including the cracks between boards, but more labor to put up, and certainly won't be an air barrier.
Charlie,
I already suggested that board sheathing was a viable option. Spruce and fir work just as well as pine, and may be cheaper.