Why shouldn’t I use ZIP sheathing?
joenorm
| Posted in General Questions on
Like many, I have never wanted to use OSB, thinking that plywood is simply a superior building product. This opinion is not really founded in hard facts, just gut feeling, really.
That said, after pouring over means of air and water sealing it seems to me that ZIP systems is a revolutionary product. To have the WRB basically done, besides seem and nail detailing saves so much time and energy.
Shouldn’t everyone be using it?
Give me your reason why you have chose not to if that is the case.
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Replies
Joe,
I am no expert- but I just oversaw the building of my home and was faced with the same questions: Plywood or Zip? I ultimately chose taped CDX plywood + WRB for our walls and Zip for the roof.
I'm glad I did. Our framers were amazing but they were sloppy when it came to firmly applying the zip tape on our sheathing. There were numerous gaps and crinkles that I suspect is common in real-world applications. I was happy to have a shingled house wrap applied over our taped plywood sheathing. Zip is perfect in theory but I think there are weaknesses in its application.
Another quick story: Our house features an interior wall that is free-standing (not attached to the ceiling). It was unstable so I decided to sheath it with leftover plywood and Zip in hopes of securing the wall before drywall. I used two sheets of 5/8" CDX plywood and 2 sheets of 5/8" Zip panels. Both had been under a tarp for a month in separate piles sitting on lumber about 3" from the moist ground. When I pulled the sheets from the piles, the plywood was still 5/8" thick but the Zip had swollen to 7/8"!! Although it eventually 'shrunk' as it dried it never fully returned to 5/8". Although its probably fine, I worry about a product that holds that much moisture- especially in thicker walls like ours (12" double stud).
I thought about zip for a while. I didn't like the fact that it requires good workmanship to seal up all the harder transitions.
Right now locally it is twice the cost of osb. If a buy osb and a high quality European sealing tape I am still well ahead on cost.
However one of the main reasons is because I'm using exterior foam and I want my windows to be outties. In this case the wrb needs to be outside of the exterior foam.
Steve
Without exterior foam, Zip may not have enough perms to prevent moisture problems.
I'm not convinced that non-shingled WRB is good enough.
I've built with all three in some pretty harsh environments, Pacific Northwest winter for instance, and they all have their advantages and disadvantages.
Plywood is great, but it's expensive and not as bulletproof as many think. Get it soaked and it will delaminate. In my current build the underside of our plywood roof sheathing has become covered in mold while the Zip wall sheathing has not. This is a new situation so don't know exactly why it's happening yet, but it happened right after we went from below freezing to 60 degrees and pouring rain in a matter of hours so yeah...could be from condensation.
OSB is nice and cheap and as long as you can get it in and covered without it getting soaked it's fine.
Zip is definitely a much higher grade of OSB than any of the others I've worked with. Try driving a nail in both regular OSB and the untreated side of Zip and you'll feel the difference immediately. Don't soak the edges of Zip or you will get mushrooming eventually, but unlike OSB the surface of Zip can take a lot of water without issue.
The big advantage of Zip is the system. WRB, taped seams, and done. Taping plywood and then tacking on Tyvek might get you close, but it's more labor and more cost in the end.
Hi Joe -
I don't think there is a way to structurally sheath, air seal, and WRB that does not rely on quality workmanship. Yes, with ZIP you have to get the depth of fasteners and the tape done right, but every system has touch-points like that.
I do like the new ZIP imprint roller; really easy to tell if enough pressure has been applied when the tape is installed.
Peter
Since it's such a new product, how do we know the whole outer layer will not fail in 20 years?
What is the ZIP membrane made out of?
You could also ask what if the plywood factory got a bad batch of glue and it all delaminates in a year? or any number of hypotheticals.
I've seen Zip being used for at least ten years now, so if there were a lot of failures we probably would have heard about it by now.
If by fail you mean separate from the foam behind, once it's up and fastened it wouldn't really matter.
Im a big fan of all huber products including zip. I think youre a leg up on most people for recognizing that your gut feeling is not based in reality.
Peter also hit the nail on the head, if your contractor can't put tape on, you're going to have bigger fish to fry.