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Community and Q&A

Closed-cell or open-cell foam?

Remodelpro | Posted in Energy Efficiency and Durability on

With a wall system that consists of 2″x4″ wood framed walls, 1/2″ plywood sheathing covered with #15 building paper or house wrap and sided with vinyl or cement board would closed or open cell spray foam provide some level of water resistance during a minor flood? Would the sheathing and studs be able to dry? Would rock wool be a better choice for insulation?

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  1. Expert Member
    Dana Dorsett | | #1

    Where are you located? (US climate zone, that is.)

    New construction, or retrofit?

  2. GBA Editor
    Martin Holladay | | #2

    Q. "Would closed or open cell spray foam provide some level of water resistance during a minor flood?"

    A. Neither product will prevent water from entering your house. Neither product will prevent your drywall or studs from absorbing moisture. That said, open-cell spray foam will absorb and hold more water than closed-cell spray foam.

    Q. "Would the sheathing and studs be able to dry?"

    A. The answer to that question depends on how long the flood waters stayed at a high level before receding.

    Q. "Would rock wool be a better choice for insulation?"

    A. What are your criteria for making this choice? I think that mineral wool batts could be removed easier after a flood, and would allow the stud cavities to dry quicker than if the stud cavities were filled with spray foam.

  3. Remodelpro | | #3

    Thanks Martin and Hello Dana,

    We are located in US climate zone 2A.
    This is a retrofit.

  4. JC72 | | #4
  5. Expert Member
    Dana Dorsett | | #5

    Are you stripping & replacing the siding?

    If yes, a variation on John Clark's referenced BSC article could work, getting of the structural sheathing and installing structural 2lb foam in the wall cavities instead. (It's expensive, but it works.)

  6. Remodelpro | | #6

    Thanks Dana,

    We were not planning to remove the siding. The flood duration was short, the water was relatively clean and the plywood siding dried and is structurally sound. We die considerelliminating the cavity insulation and installing EPS insulation on the exterior under the hardiplank siding with a rainscreen but the client does not want to spend that much money rebuilding the structure.

  7. severaltypesofnerd | | #7

    What's the integrity of the old siding and wrb?
    Any moisture holding insulation becomes a disaster, if water seeps in due to wind driven rain or defects.

  8. Remodelpro | | #8

    Hi Bryce,

    The existing Hardiplank siding and #15LB building paper WRB are both in good condition.

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