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Would like comments comparing 5-ply waterproof plywood with Huber ZIP wall and roof sheathing

JoeUSAF | Posted in Green Products and Materials on

I will be building a U.S. EPA Energy Star to be certified home, (24’x40′), and am trying to decide upon the best sheathing for the walls and roof.

The proposed configuration for these two are:

1. Walls (2×6, 16″ OC): vinyl siding, mesh rain screen, 3/4″ foil faced polyisocyanate rigid foam (taped), either 5/8″ 5-ply waterproof plywood or 5/8″ Huber ZIP sheathing (both taped), 3 1/2 – 4″ closed-cell spray foam, remainder of 2×6 cavity with open cell spray foam, sheetrock.

2. Unvented catherdral roof (2×10, 16″ OC, 9:12 pitch): Certainteed Landmark Solaris Energy Star Gold or Platinum asphalt shingles, #15 asphalt felt underlayment, either 5/8″ 5-ply waterproof plywood or 5/8″ Huber ZIP roof sheathing, 3 1/2 – 4″ of closed-cell spray foam, remainder of 2×10 cavity with open-cell spray foam, 1″ XPS rigid foam, sheetrock.

Would appreciate any comments on these configurations about any fundamental flaws or pitfalls and especially a comparison of the plywood versus Huber ZIP sheathing with regards to strength, durability, moisture and potential rot. Thank You.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Joseph,
    I don't have any opinion on the choice between Zip sheathing and plywood.

    But here is some feedback on other aspects of your plan:

    1. You don't need a mesh rainscreen product under vinyl siding. Vinyl siding already has air behind it, due to its configuration. It is naturally well ventilated.

    2. I don't like walls that sandwich the wall sheathing (whether plywood or Zip) between two layers of vapor-impermeable foam. The sheathing should be able to dry in at least one direction. I would skip the closed-cell spray foam between the studs, and just use the open-cell foam (or cellulose). If you want to improve your wall assembly, make the polyiso layer thicker.

  2. JoeUSAF | | #2

    Martin,

    Thank You for your technical assistance. I will eliminate the rain screen and the closed cell spray foam interior to the wall sheathing so that it can dry to the interior. I am leaning towards the use of plywood rather than ZIP sheathing, which has had a lot of hype, but is unproven over the long haul. Huber Zip gives a limited 30 year warranty, but houses last much longer than 30 years. I do not want to be forced to strip off 30 year old ZIP sheathing with the spray foam attached behind it. Plywood has been a proven durable, moisture resistant product for 50 years. Once again Thank You for your assistance.

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