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Are the more exotic WRB’s any better than Tyvek?

Joe Norm | Posted in General Questions on

Hello.

I am in the middle of framing a house. I last minute opted out of Zip System for sheathing and have started in with CDX ply.

I have a few questions now. For airtightness I was planning to tape the seems of the ply, but was wondering if it would be a better idea to just tape all the seems of the WRB instead? Is this as good as taping the plywood from an air barrier perspective?

I’m also curious about how “worth it” some of the different brands of WRB’s are. I priced out VaproShield IT and it looks to be 3x the cost of tyvek. Solotex Mento looks to be about 2x the cost.

Why are these products so much more and how are they justified over Tyvek?

Thanks

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Replies

  1. User avatar GBA Editor
    Brian Pontolilo | | #1

    Hey Joe,

    I just wrote a lot about this (links below) and unfortunately, there is no easy answer when it comes to the performance of individual products. They all pass the same tests to be approved by the ICC-ES (code approved), but those reports don't offer any more info than which tests they passed and what they are approved for. You can clearly see that some of these products are more robust than others, but the question is: does it matter if they are installed properly and if water is managed well on the house in general (roof overhangs, flashing details, etc.)?

    It is well known that staple up housewraps like Tyvek don't make the best air barriers. At least they are challenging, at best, to detail as an air barrier. If you choose this type of product, taping the plywood seams is a more straightforward approach to air sealing. If you want your WRB to be the air barrier on your walls, panel products like ZIP, peel-and-stick products like Henry Blueskin, or Fluid-applied products are a better bet.

    One more thing, almost every expert I have talked to about this suggested that the best possible thing we can do to prevent WRB failure is to ventilate our siding with a rainscreen installation.

    https://www.greenbuildingadvisor.com/article/the-complicated-role-of-a-water-resistive-barrier
    https://www.greenbuildingadvisor.com/article/keeping-water-out-of-walls-housewrap-and-beyond
    https://www.greenbuildingadvisor.com/article/nine-water-resistive-barriers-worth-knowing-about
    https://www.greenbuildingadvisor.com/article/wrb-faq-thats-water-resistive-barrier

  2. Jamie B | | #2

    Hey Joe,

    I agree with what Brian said.

    I went through the same question when I was framing my current build.

    It's more a question of durability and what your assembly is going to be. Tyvek works well as an WRB and is permeable. My assembly has 2" of rockwool board over top of the WRB, so I went with Tyvek because I figured the insulation sitting on top of it would hold it down, protect it over time and be another layer for any water that makes it passed my siding.

    Otherwise if I wasn't doing exterior insulation, or I wasn't there to do the air sealing of sheathing, then I would have gotten an (unfortunately) 4x more expensive peel and stick just to have better assurity. Solely because I think peel and sticks look like a more robust product

  3. Malcolm Taylor | | #3

    Joe,

    I use Tyvek Commercial because it is a lot tougher than regular Tyvek, making it easier to install and work around.

  4. George Smith | | #4

    "One more thing, almost every expert I have talked to about this suggested that the best possible thing we can do to prevent WRB failure is to ventilate our siding with a rainscreen installation."

    Brian, do you think that this applies when using vinyl siding?

  5. User avatar GBA Editor
    Peter Yost | | #5

    I have a strong personal preference for rigid air barriers rather than sheet good air barriers. I know you are asking about the differences among sheet good products, but...

    Vinyl siding is of course hung rather than fastened to the exterior wall. It's about as close as you can get to a ventilated rainscreen without actually having one. The free drainage and air circulation within the cladding provided quite good moisture performance.

    Peter

    1. Joe Norm | | #8

      Peter, I am actually siding with corrugated metal oriented vertically and reverse board and batt.
      I do this because I like the look and they seem to me to be inherent rain screens without having to add furring strips.

      1. Malcolm Taylor | | #9

        I'm confused as to where the discussion about vinyl siding came from?

        Vertically oriented corrugated metal siding meets the definition of a rain-screen under our code.

  6. User avatar GBA Editor
    Brian Pontolilo | | #6

    George,

    Some builders say that it doesn't apply with vinyl, but I can't answer that question with any confidence. In theory, vinyl has inherent draining potential. But it still has a nailing flange that is fastened tightly to the wall, which could hold up water. That water, held indefinitely against the siding is thought to be the culprit for some WRB failures.

  7. Scott Wilson | | #7

    What about liquid applied WRB's?

  8. User avatar
    Jon R | | #10

    There are cases where exterior perms definitely matter and something like Typar will outperform too permeable Tyvek HomeWrap (which can allow excessive inward vapor drive).

  9. AlexPoi | | #11

    The thighter your house is, the better your wrb has to be. A little bit of water in a leaky house is not a problem because air movement will dry the sheathing petry quickly if it gets wet (if you have a drain gap behind the cladding otherwise you are screwed). But if your house is very thight and there is not so much air circulation, the only way your sheating can dry is through water diffusion which is much slower. Note that plywood is a bit more robust than OSB in terms of water as it can hold more water before being damaged.

    So if you are building a tight house with osb sheating in a wet climate, I would personally not take the risk to cheap out on the wrb just for the peace of mind. After all, a good wrb will cost you just a couple of thousand more but could save you big time. There is no easy answer there unfortunately, just think if you are willing to take the risk or not. You should focus on the flashing before thinking about the rest of the walls though as it is where the damage happens most of the time.

    1. Joe Norm | | #12

      I think this is the question.......what makes a good WRB? Installation details are #1, but are the fancier, more expensive wraps any better than the more affordable ones if all the details are done right.

      Liquid applied is out of the question.

      thanks for all the replies

      1. Malcolm Taylor | | #13

        Joe,
        I agree. If the WRB is installed diligently, I haven't seen much to suggest any WRB yields a significant advantage over another.

      2. Andrew C | | #16

        @ Joe –
        You kind of asked two different questions. One was about air barriers. Taping the seams of your plywood (yes!) sheathing seems to be one of the most robust ways to do this.

        The second question was about WRBs, emphasis on the “W”. Properly detailed, the WRB can be a belt-and-suspenders backup air barrier to the taped sheathing, but the sheathing remains primary.
        As others have pointed out, flashing design details and attention to these details, along with avoiding dumb designs like dead-ending a roof valley into a wall, are critical to durability. [Don’t forget your kick-out flashing – I’d like to talk with the designer of our current place by hand…grr.]

        IMO, after seeing MANY different wall designs proposed here, I think you are onto one of the best: taped plywood sheathing for your primary air barrier, with Tyvek Commercial as your WRB.

        1. Joe Norm | | #17

          Thank You! I will tape the seems of the ply.

  10. Joe Norm | | #14

    One difference I see with Vaproshield IT is that you are supposed to staple only the where another sheet will come and lap over it. It would be nice to have a shield that is free of holes.

    I looked at the Tyvek Commercial. The price compares to Solotex 1000. The 9 month exposure time is handy.

    1. Malcolm Taylor | | #15

      If you install it with cap fasteners there are effectively no holes that can leak. Personally I don't think the holes from staples are ever a problem.

  11. Patrick OSullivan | | #18

    > I last minute opted out of Zip System for sheathing and have started in with CDX ply.

    Could you share why you last minute opted out of Zip?

    1. Joe Norm | | #19

      No good reason really. I'm not fond of OSB in general and I couldn't totally get past the idea of hundreds of feet of reverse laps for water to get caught up in.

      I'm sure Zip is great and in the end I may regret not trying it out.

      1. Malcolm Taylor | | #20

        I don't know... Zip-R makes some sense to me, and I'm pretty sure Zip will turn out to be a good long -term Sheathing/WRB, but I can't see regretting using taped plywood and a sheet WRB. They do the job they are designed for very well.

        1. Zephyr7 | | #21

          I have often wondered about the difference in durability between zip and plywood. I know zip made from a good grade of osb, but osb in general doesn’t hold up as well as plywood when exposed to moisture over a period of time.

          Has anyone ever actually done any tests comparing zip and plywood for long-term durability?

          Bill

          1. Alex P | | #23

            Steve Baczek has left two small pieces of Zip taped together on his wood pile for the last 10 yrs. He says the tape is perfectly fine and the edges have swollen a little with full exposure to rain, ice and snow.
            See here
            https://www.instagram.com/p/Bxqd6gcDoQI/

        2. Joe Norm | | #22

          Thanks, and as long as we're on this topic, what is your preferred brand tape for plywood seems?

          I was wondering if I could just use tyvek or typar tape for this or should I go with something more durable like 3M all weather tape?

          I have read the relevant articles but I will revisit them now.

  12. Joe Norm | | #24

    Alex P- That is pretty impressive. If I saw a photo like that 2 weeks ago I'd probably be using Zip right now.

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