House Sheathing/Wrap Question
Hello. We are in the process of building a custom home in Central VT. We are struggling with selecting a sheathing method. For a variety of reasons, we would prefer to err on the side of not relying on tape that may or may not be well adhered. For similar reasons, and the fact that we are heading into winter, I think a stick-on WRP is not a viable option. So, we are thinking either plywood or OSB with commercial Tyvek (and we would make sure it is attached with cap staples/nails per installation instructions). The commercial Tyvek counts as an air-barrier, and gives us a nice long runway for getting to siding. We are planning on a rain screen. Does anybody have any advice for OSB vs Plywood? Is it best practice to still tape the joints of the sheathing before wrapping? I assume we could use 3M or Zip or other products for that, and it would not necessarily need to be rolled, just pressed on? I think the vast majority of folks have moved on to Zip, so I don’t see a lot of recent advice about the more “old-school” sheathing methods. Thanks so much!
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I recently built my house in southern VT and used zip sheathing and zip tape. All the research I did pointed to the fact that a tyvek wrapped house wouldn't be as air tight as zip sheathing with tape. My house was inside for over a year and the sheathing and tape was still in perfect condition with no leaks when I went to put on the siding.
Tyvek is a WRB but not an adequate air barrier. You can easily tell this by observing a wall under construction with mechanically fastened house wrap and watching it flap when the wind blows. If you don’t want to rely on tape, have you considered a fluid-applied WRB? It goes on not dissimilar to a thick paint. You can get trowel grade, roller grade, or a thinner spray grade variety.
BnBnVT,
Plywood and commodity OSB have the useful characteristic that they becomes more vapour-open when damp - much like a variable-perm membrane does. Plywood handles these swings in moisture better than OSB, which can swell. Zip has the advantage of not needing an additional WRB, but it has a constant vapour permeance of about 3.
Like Malcolm said -- Plywood will be more open to vapor than OSB, mainly due to the high glue content in OSB. Choosing one or the other is not going to make or break a wall assembly, but it is a consideration. I personally prefer plywood because of this vapor characteristic, and I find it more durable. OSB costs less money and the sheets lay flatter. I would recommend taping the seams, taping to the foundation, and detailing the roof wall intersection. This makes the sheathing your air barrier. Then detail the tyvek or whatever you want as your water barrier. All tapes need to be rolled/pressed. Tapes with acrylic adhesives should work fine in cold weather, I use them through the winter In VT with no problems. If you are really concerned, 475 is selling a winter specific tape --Tescon ARKTICC
The acrylic tapes (ie 3m8067 or ZIP) work without issues in freezing weather. The important detail is to roll them, this is much harder then it sounds for trades to do. Might be simpler to DIY after hours.
Taped sheathing is the easiest and most robust air barrier. Doesn't matter ZIP/OSB/CDX, tape the seams. My preference is CDX with taped seams and Tyvek commercial for housewrap. The thicker housewrap can really take a beating so it takes the pressure off having to side.
My preference is to tape the sheathing, install exterior rigid + house wrap and rain screen strapping before raising the wall (the is easy for me, but might not be for your crew). This gives you a weather tight wall in one step, in case of exterior rigid some insulation to take the edge off during a winter build. You do have to do some extra detailing at the corners and at the bottom of the wall but those are not that hard as long as planned for ahead of time.
Your statement about it being harder than it seems is my "reasons" in the original post! Sadly, our wall is about 19' tall, so while we could certainly do some DIY for the lower stuff, it's going to be impossible for the higher stuff. Interesting idea about your wall construction process. We will have to think about that a bit.
There are so many options, and we see so many designers and builders using every combination of products and assemblies under the sun these days. And, as long as you're following some general fundaments and understand the control layers, there are many different ways to design and build a durable wall. I think taped sheathing and a mechanically fastened WRB are an excellent choice. You're replying on the tape for air sealing, but not for water management, because you can lap the WRB and integrate flashings shingle-style for drainage (use a rainscreen detail). Depending on the tape and WRB you choose, this could be one of the most economical options too.
Use something like pro clima tescon vana tape. It does require pressing firmly, but not as fussy about rolling as zip. Tape your sheathing as air barrier and go tyvek commercial for wrb. The tescon is a little more expensive but very sticky and easy to work with.
We did zip taped plywood. Most contractors have done zip. I bought the roller and had it on site for them. Since the zip tape is not my WRB, I went cheap and bought it from a roofer who had leftovers on Facebook.
Zip also has a great first time builders rebate. $200 back on tape, $200 back on stretch tape, and $200 back on liquid flashing. So all my sills are stretch taped and my foundation to plywood is liquid flash. Over top of all this, I have Pro Clima WRB.
Is there a particular grade or type of plywood that is easier to work with? What did you use? Our builder used plywood a few houses ago on a job at the customers request, and said it was a real pain to work with since it was not uniform (like OSB is). Obviously exterior grade. :)
I do not have full confidence that the requirements of the Zip system taping will be met per installation instructions. I assume (and this is why we're making the decision against Zip), that the tape on plywood or OSB, which is then covered by Tyvek Commercial, is going to be a lot more forgiving to lack to full compliance on taping than Zip Sheathing will be.
Not rolling the tape on the seams of plywood or OSB will result in a leaky and under-performing house. If you don't think the crew is capable or rolling tape then I would rule out any method that requires rolling tape, even plywood/OSB. Have you looked at fluid-applied WRB's?
I have thought about it, but worry that we would find anybody with the expertise / equipment to install it in rural Vermont. We might be able to find somebody from Burlington who does it and would be willing to travel. I'd also need to check into temperature requirements for installation. It's a good idea to dig into more though. Thanks!
Material: 5-gallon bucket of the WRB of your choice and a paint roller on a stick. No spray rig needed. No expertise needed. Maybe some scaffolding to get to the high parts of to wall but you’ll have to have that anyways for siding installation.
I'm not a framer but have installed a bit of CDX. I have never had issues with it being "even" Any rough framing will have more error in it than the CDX.
1/2" CDX defiantly does not sit flat but a nailer will pull it nice and flat without issues.
We used standard grade CDX. Some of the edges are a bit wavy. If we had not gone with a 3/4" rain screen, our framer advised that it might show through to the siding. He convinced me to purchase 5/8 OSB for the roof instead of 1/2" CDX. He's the one lifting them, not me! Our roof is vented, so I was less concerned about that.
I haven't heard of any issues with Zip tape not staying stuck to Zip sheathing IF the tape is rolled. Huber prints right on the tape that you have to roll it too! It's not the fault of the tape if it fails after being incorrectly applied. I think you're safe with Zip sheathing and Zip tape.
Anyway, if you want to go old school, I'd go with plywood -- especially since you're thinking you're going to have the sheathing exposed for a period of time. OSB is more prone to swelling and issues at the edges when it's exposed to the weather. Plywood is likely to hold up better, and it holds fasteners a lot better than OSB. I would still try to get the WRB up though to protect the plywood from getting rained on as much as possible.
Bill
Thank you all for your extremely helpful replies!!! This was super helpful to us in thinking through the various options!!