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EIFS in combination with interior spray foam insulation

strategicbuild | Posted in Energy Efficiency and Durability on

I would like to design a wall system using EIFS stucco with an interior spray foam insulation. I live in north east Colorado which is in climate zone 5. The EIFS eps would probably be 1.5″ over Tyvek stuccowrap wrb, or a similar product. My wall sheathing is 7/16 osb.

On the interior, my walls are 2×6. I would like to apply 1″ closed cell spray foam followed by a kraft faced insulation bat of either R-13, which would leave about .5″ of an air gap between spray in and fiberglass. Or R-19 kraft faced fiberglass which would come in contact with the spray in foam.

I like the idea of the closed cell spray foam adding rigid strength and reducing the air infiltration. Should I be concerned with vapor from the interior getting trapped between the fiberglass and closed cell foam? Usually in the winter, we struggle to keep the interior humidity at or above 30%, but I understand water vapor no matter the percentage can still condense on a cold surface.

What other concerns should I have with this type of system, and how can I improve it? I would certainly appreciate any product recommendations and techniques.

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  1. GBA Editor
    Martin Holladay | | #1

    There are two problems with your plan:

    1. The EPS layer has an R-value of only R-6, which is insufficient for your climate zone. You need at least R-7.5 of EPS (2 inches). For more information on this topic, see Calculating the Minimum Thickness of Rigid Foam Sheathing.

    2. If you want to install exterior rigid foam, you shouldn't install any closed-cell spray foam between your studs. To learn why, read this article: How to Design a Wall.

    1. 2010G37X | | #2

      Hello Martin

      I am reading your response and I thought j ask a couple of questions.

      Would the ccSPF of 1" R6 be added to the R6 EPS of the outside, and technically (and theoretically) meet the minimum thickness of Exterior sheathing?
      I say this because:
      Imagine a flash and batt scenario with no exterior sheathing.
      All you would need is 1.5 to 2" to get that R7.5.
      Since the ccSPF is air Impermeable (sorry I know you already know all this stuff)
      No exterior insulation is needed,

      However adding the exterior insulation only helps the overall assembly by rasing the sheathing tempertute, even though it doesn't raise it fully, it doesn't matter because of thr air Impermeable ccSPF.

      I looked at your Point 2, and I think i am missing which exact reference you are referring to.

  2. 2010G37X | | #3

    Besides my comment above

    What did you end up doing or finding?

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