Zip or CDX??
Rainbirdd
| Posted in General Questions on
Random question
My lumber yard currently has 1/2″ CDX and 7/16″ Zip priced the same.
I had originally planned to use Adhero 3000 as my wrb over CDX for a new residential build in a cooling predominant climate – zone 3, coastal southeast.
If I wanted to use the Zip AND Adhero 3000 together, should I be concerned about the combination of the two not being vapor permeable enough? I know OSB is not super vapor permeable, but my concern would be that since Zip is OSB with a air control layer, it will effectively create a vapor barrier….
Any thoughts?
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Replies
This an an either or kindof situation. Either use CDX+adhero or ZIP. Both will work equally well if detailed properly. I'm a fan of CDX but I seem to be the minority as most builds nowadays use OSB.
Yes - I understand that it's redundant, but then again, this house is in a hurricane prone area, so I like to go above and beyond to increase the durability of typical construction.
My opinion is that Adhero is a better product and more performative than ZIP, so I'd like to use it regardless. It just felt odd to me that I could get ZIP for the same price as CDX...
Adhero is around 10 perms so it will hardly impact the perm rating of Zip sheathing alone.
Combining the two will void part of the Zip warranty but I often add a loose WRB to Zip which also voids the warranty but provides a more robust product.
I was a fan of plywood sheathing until recent years when it seems to be very poor quality--lots of voids, delaminations, as flat as a potato chip, etc.. Zip is nice to work with, though I prefer plywood's higher permeance.
Thanks for the insight Michael.
If you had to pick, would you just go with Zip + Tape all the way around? Or would you still prefer a product like Adhero + CDX? - Assuming plywood quality is decent enough (down here we usually have southern yellow pine).
I've been kind of set on using Adhero over the Zip system bc it seems like a much more performant product, but maybe I've created an unjust bias towards the product in my own head lol..
I'm a fan of Zip for many reasons but I would consider good-quality plywood and a separate WRB a superior assembly, if airtightness is managed at least as well as it is with Zip. That's in my market, which is dominated by heating and primarily outward vapor drive, and easy access to high-quality, low-carbon insulation such as cellulose and wood fiber. The reason is that the sheathing will experience periods of elevated moisture levels and I trust plywood to remain structurally sound over 50-100 years vs. OSB, even high-quality OSB such as Zip.
In your climate zone, inward vapor drive is a higher concern, and your insulation choices are likely different, which changes the equation. What are your plans for insulation, rain screen and cladding?
Current plan is to insulate with Hemp or Fiberglass batts, rather than spray foam. The rain screen will likely be a cross-hatch of 1x3 + 2x4 to accommodate the vertically hung T&G pine siding and trim profile. This is why I prefer the monolithic air barrier approach.
If in hurricane are, I would bump up the sheathing thickness and go for CDX with either taped seams or self adhered. Either will work just as well as long as detailed properly.
> Combining the two will void part of the Zip warranty but I often add a loose WRB to Zip which also voids the warranty but provides a more robust product.
I've not seen before commentary about this voiding the warranty, so I'd be curious to hear where you got that feedback! I have Obdyke FlatWrap on top of the Zip on my own house, but that was mainly because it was left exposed longer than allowed. It was still in perfect shape, but I did it for peace of mind.
From a tech doc (https://www.huberwood.com/uploads/documents/technical/Housewrap-over-ZIP-System-sheathing-Tech-Tip-Wall-ZIP-System.pdf): "Installing a mechanically-fastened water-resistive barrier over ZIP System sheathing or ZIP System R-sheathing will not void the ZIP System 30-Year Limited Warranty. However, Huber Engineered Woods is not liable for any damages caused by improper housewrap or flashing installation. It is the responsibility of the general contractor, designer-of-record, or other authority having jurisdiction to incorporate proper flashing materials and techniques when using a housewrap product over the ZIP System."
I first heard it through a client I was consulting for after their house experienced massive siding and sheathing failure after just 2-3 years. The culprits were many, but part of my proposed solution was to replace the rotted sheathing with new Zip sheathing and a separate WRB to ensure that all flashings could be mechanically lapped. My client checked with Huber to make sure that was ok, and found that it would void part of the warranty.
I don't recall exactly how it changes the warranty, just that it does, but not in its entirety. I also see Huber's head of building science at a conference once a year and asked him about it, and he explained that they just can't predict how a given WRB will interact with Zip or who is really to blame if there were a failure. It gets muddy quickly so they're just protecting themselves from potential litigation.