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Open Cell vs. Closed Cell in a Hot-Humid Climate

marc.kleinmann | Posted in Green Building Techniques on

I am doing some research on the open cell vs. closed cell issue in a location that is on the borderline of zones 2/3 – Dallas, TX. The majority of what I’ve found in my research so far suggests that open cell should be used over closed cell in this climate. My research is based on articles found on, some articles on this website as well as input from several other builders and green building experts. There’s a new spray foam company in town that moved in our market from Austin and they are pitching AirTight closed cell foam made by Lapolla. Reading the product specs, the CC has a permeability rating of 1.98 @ 1″. I would like to hear as much input as possible from people that have worked with closed cell in this climate or have a deep understanding of what this does to the wall assembly. It seems to me that this would move the vapor profile to the inside of the wall cavity. Thx in advance for your input on this subject.

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  1. homedesign | | #1

    I am in your vicinity...Plano actually
    Your question is very complex...
    Contact me if you would like to stop by and chat about Low Energy Home Design.
    [email protected]

  2. Riversong | | #2

    Describe your wall section. It functions as an assembly. Discussing the properties of one element is impossible without some context. What are your HDD and CDD? Typical summer relative humidity?

  3. marc.kleinmann | | #3

    outside to inside: brick/ventilated cavity/housewrap/osb/6" stud wall/5/8" drywall, painted.
    According to US DOE map right on border of zone 2&3
    HDD 2200 (@65) - per NOAA
    CDD 2900 (@65) - per NOAA

  4. Riversong | | #4

    Since you're in a predominantly-cooling climate and the dominant moisture drive is from outside to in, even with the (how well?) ventilated cavity it makes sense to keep the inner wall vapor open for drying to the inside. The most important factor is to avoid an interior vapor barrier that is significantly cooler than the ambient air.

    Sufficient foam insulation - of either type - will almost certainly keep the sheathing above the summertime dewpoint, except perhaps at the thermal bridging of the studs, but it's always a good strategy to allow as much drying potential as possible.

    Given that you don't need high R-values in your mild climate, I would agree that open-cell foam would be preferable to closed-cell.

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