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Mykcuz2000 | Posted in Building Code Questions on

Would I be code compliant if I installed 1″ thick xps directly to studs, taped all seams, then nailed 1/2″ plywood according to hubers zip r nailing requirements(1 1/2″ penetration into studs, and wrapped in tyvek?

Cheaper material, continuous insulation of r6, plywood is superior to osb, solid nailing for vinyl siding.

My intended use is for the gable end(load bearing wall) of my one car garage. Future conversion to interior space as office.

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  1. Expert Member
    BILL WICHERS | | #1

    No, you would not be code compliant in terms of Huber's specifications. You can't make your own version of Zip-R because Huber has done testing on theirs so their specifications and nailing schedule are only valid when used with their product. Huber has control over their manufacturing process which is required for their final product to meet the specifications and to function the way the tested samples did.

    Why don't you just build in the usual way, with the sheathing nailed directly to the studs, then install your rigid foam on the exterior side of the sheathing?


    1. Mykcuz2000 | | #6

      Ok, say leaving Huber out.
      I can sheath the stud wall traditionally, then install 1" foam board to the exterior, but I can't reverse the order of install because the plywood is not approved to be installed exterior to foam board? So boise cascade would have to test their plywood over foam board and be approved for that application, in order for it to be code compliant?

      1. Expert Member
        NICK KEENAN | | #8

        There are two types of codes, prescriptive and performance-based. A prescriptive code says "if you do it this way you're OK." An example would be a joist span table, so long as you follow the table you're OK. A performance-based code says you have to meet a certain performance goal, how you get there is up to you. An example would be saying that a floor has to be capable of supporting a certain number of pounds per square foot.

        People generally prefer prescriptive codes, because any schmuck can read the code book and build that way. When you have a performance-based code you need to get someone with a bunch of letters after their name to review your plans and certify that your design will meet that performance.

        For exterior framing, a prescriptive code might read say either 2x4 on 16" centers or 2x6 on 24" centers, clad with a sheathing approved for this purpose and installed in accordance with the manufacturer's instructions. A performance-based code might say "an assembly capable of withstanding all anticipated structural, wind, snow and seismic loads."

        So if you're not going the engineered route you can't use materials outside of the way they have been approved to be used.

        1. Expert Member
          NICK KEENAN | | #9

          When you go to the lumber yard you might notice that all the lumber has stamps on it showing it's purpose. A piece of plywood might be stamped "sheathing" and "sub-floor," even the 2x4's are stamped "stud." You can't use something in a structural way if it's not stamped for that purpose.

  2. Expert Member
    Peter Engle | | #2

    No, that would not be code compliant. Huber has performed lots of analysis and testing of their composite product. Your DIY product will be "different" and not covered by their work. It also doesn't meet the prescriptive requirements for nailing in the building codes. Why not just put the insulation outside the sheathing? With 1" thick insulation, you can fasten the vinyl right through it. Sure, there's a bit more thermal bypass with the nails, but not enough that you'd notice.

    1. Mykcuz2000 | | #3

      Please forgive me, just trying to comprehend. Zipr is code compliant because they tested their own product, but it is not code compliant to install 1" foam board and then sheathing, under any circumstances?
      You cannot build a similar wall assembly without buying the brand?

      I would think logically, if 1/2"sheathing over 1" if foam is an acceptable assembly, why would you be bound to paying huber?

      I am attracted to this assembly because it provides cost savings and a superior nailing surface for siding, without requiring additional material for nailers.

      1. AlexD2022 | | #7

        If you want an assembly like that but don't want the huber product you would have to speak to an engineer and have them stamp the details (if they come up with a code compliant way of doing it in the field). Depending on where you are you might not need much, if any in the way of sheathing which would provide you even more cost savings.

  3. Jon_R | | #4

    > not code compliant to install 1" foam board and then sheathing, under any circumstances?

    Sure, it's compliant for any wall that doesn't rely on the sheathing being there. My brother-in-law has only the foam.

  4. Expert Member
    BILL WICHERS | | #5

    >"I would think logically, if 1/2"sheathing over 1" if foam is an acceptable assembly, why would you be bound to paying huber?"

    You're not "buying a brand", you're paying for an engineered product that is made to a certain set of specifications that have been tested by a third part testing lab to be safe in certain types of assemblies when installed in a certain way. This is similar to an electrical device that is "UL Listed". The "UL Listed" means that the manufacturer has sent a sample of their product to UL, which tested it, and keeps a record of this on file. When you buy that product, you know that there has been testing and approvals to make sure it's safe in it's particular intended application. Companies have gone out of business for playing games with this. It's not an arbitrary thing.

    This has all been incorporated into the codes with the "must be listed for the purpose" language. "Listed" means the product was tested and certified by a nationally recognized testing laboratory. In the US, that usually means UL, CSA, or ETL (I'm most familiar with the electrical stuff). You can't just start up your own testing lab to certify your own product, it doesn't work like that.


  5. Expert Member
    BILL WICHERS | | #10

    >"So if you're not going the engineered route you can't use materials outside of the way they have been approved to be used."

    It's probably worth adding that if you DO go the engineered route, you'll need a licensed engineer to seal the drawings of what you're going to do to get past inspection.

    Ultimately all this stuff is about structural safety and no one wants to have a structural failure that gets someone hurt.


  6. Expert Member
    Peter Engle | | #11

    Jon has an important point (#4, above). Sheathing provides several functions on a house. Structurally, it provides racking strength that is, strength against your house sort of moving sideways with the walls turning into parallelograms. The amount of racking resistance you require is based on where you live. In areas with high wind or seismic loading, you need lots. IN other areas, you don't need as much. And, you can get racking protection without sheathing. You can use let-in wood bracing, or steel strapping. In many areas, you can get all the strength you need from a single sheet of plywood at each corner. If you are in one of the low-load areas, the sheathing is literally only used as a nail base for the siding. In some of those areas, cardboard sheathing is commonplace. In some only foam insulation is used with nothing else. The siding gets nailed to the studs.

    Where are you located?

    1. Mykcuz2000 | | #12

      Northern nj, no seismic or wind concerns of any kind. I've seen plenty of cardboard sheathing on older homes.

      Im talking a basic 8'tall garage wall. Just trying to figure out if there's a compliant alternate version of what zipr is doing. Literally upgrading over zip by using plywood. Not reinventing the wheel.

      1. Expert Member
        Akos | | #13

        The reason you use ZipR is that it saves labor. You only need to install one sheet good and you are done.

        Your assembly, you are installing two layers, there is no labor savings by mimicking ZipR. It is the same labor to install the rigid under the sheathing as over the sheathing.

        With the sheathing directly over the studs and foam over the sheathing, you have a much stronger and stiffer assembly that any building official will readily sign off on.

        1. Patrick_OSullivan | | #14

          > The reason you use ZipR is that it saves labor. You only need to install one sheet good and you are done.

          Very true. Sadly, it's often hard enough to find a framer who can install and tape Zip properly. But if you do, the learning curve to jump to Zip R is essentially nil.

          But Mykcuz2000, if you want to go exotic, since you're in NJ, Peter Engle is a licensed engineer and maybe he'll take your money to design something bespoke. ;-)

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