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· Administrator
14,337 Posts
Discussion Starter · #1 · (Edited)
Is this a superior product compared to traditional methods?

What are the cost comparisons to this and the standard sheathing/wb/flashing detail?

How do the flashing details work, or do you need any?

What about the seams? I know you tape the seams but…..must be some darn good tape.

· Registered User
11,730 Posts
Haven’t used it yet. With a perm rating of 13-16 on the outside coating and even less on the tape, I would research it some. I would push a rain-screen system with f.c. or Cedar, unless down South with >20” rain. Or at least ply or OSB and stucco wrap w. wrinkles to divert water, even behind vinyl.
That gives you an all important slight gap between sheathing/siding to drain the sun-driven moisture from behind the f.c. board in walls
You would not get that w. Zip unless rain-screened. It is a denser product than OSB, holds the edge swelling better;

If it ever did get wet, would take a looong time to dry because of the low perm coating. I used to push Typar over Tyvek, used to…. Tyvek- 58p., Typar- 16p.
Tyvek and OSB, saturated test; took >15 days to get to 10%----low perm wrap (similar to Zip) took 65-70 days to 10%. Page 15;

Same page; no mold on OSB/Tyvek---83% mold on 11perm. wrap- similar to Zip.
Remember that’s with a water leak not minimal inside/outside diffusion. You don’t want to see the Ply vs. OSB………I’d have to search library for it. Like any engineered wood, keep it dry, it’s fine. Not with a low perm coating though…..
pp.17, above conclusions--- 18-24p window. Hmmmm.
Sorry couldn’t help you more.


· KemoSabe
644 Posts
I've used it on a roof. It seems like a decent product, but the edges WILL swell if exposed to wetting for too long.

The tape is super tacky, but must be rolled for proper bonding. If you use the system, I recommend the dispenser highly.

I'm still not convinced on wall applications, not only for permeability reasons, but for proper flashing details at critical spots.

Call me crazy, but I'm still a fan of #30 ASF, especially over OSB. The Variable Permeability of felt is a distinctive feature that "holds alot of water" in my book.:whistling2:

· Registered User
11,730 Posts
Zip (or OSB) should never be used with spray foam inside. The moisture has no where to go but into the sheathing and can not dry to the outside with the low perm coating; “When placing a foam product in an
exterior wall assembly, ensure that the
moisture flowing through the foam will
not affect other materials. This could
happen when moisture is trapped in a
moisture-sensitive material, such as
plywood or OSB, and drying is prevented
by the layer of SPF. It could also happen
when moisture accumulates in the outer
layer of the spray foam, which could
damage moisture-sensitive materials
such as sheet metal.”

Of course OSB would have a high perm.WRB rather than a low perm. coating, making it dry faster.

I believe we will see more of the product used simply because it easier to get a WRB with it, though it’s still on an OSB backer, even denser- essentially a vapor barrier. Then there is the sheathing temperature/dew point concern with OSB (Zip). How many builders will be installing only enough (past min.code) exterior rigid insulation rather than insulating to lower the dew point of the inside face of the sheathing. Footnote “H”;

Figure one and be surprised;

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