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Do I use Tyvek between OSB and taped blueboard?

Bob Spontak | Posted in Energy Efficiency and Durability on

Building exterior walls: 2×6, 2 ft. o.c., with dense-packed cellulose, 7/16″ OSB with 1-inch Dow blue board, taped, then vinyl siding.

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  1. GBA Editor
    Martin Holladay | | #1

    When you write, "Dow blue board," I assume that you are talking about Styrofoam (XPS foam insulation) with an R-value of R-5 per inch.

    First of all, I hope you live in Climate Zone 4 or somewhere warmer. Because if you live in Zone 5 or somewhere colder, your exterior rigid foam isn't thick enough to keep the OSB above the dewpoint in winter. For more information on this issue, see Calculating the Minimum Thickness of Rigid Foam Sheathing.

    Second, every wall needs a WRB (water-resistant barrier). A WRB is required by code. You can choose to use Tyvek as your WRB if you want -- that's what I recommend -- or you can use the rigid foam as your WRB. (This last option often raises complications when you try to integrate the WRB with your flashing.)

    If you choose to use Tyvek as your WRB, you can install it under the rigid foam, or over the rigid foam -- your choice. Just make sure that your WRB is integrated with your window flashing.

    For more information on these issues, see these three articles:

    All About Water-Resistive Barriers

    Using Rigid Foam As a Water-Resistive Barrier

    Where Does the Housewrap Go?

  2. Bob Spontak | | #2

    Thanks for the reply. I do live in zone 4 so the I" should do the trick. I've decided to use duponts drain wrap between the plywood and the foam. I feel that's will be my best option.

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