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Foamboard and WRB for Unconditioned Enclosure

Bruce_Davis | Posted in Energy Efficiency and Durability on

Cold edge of Zone 4. See picture of 600 sq ft unconditioned walk-out storage space/proposed art studio (no further finishing) under suspended garage. Stays cool enough in summer with portable dehumidifier connected to floor drain. For most of winter, with indoor temps usually 40-50F, a space heater should be sufficient when using as art studio. During severe, sub-zero cold period last winter, did drop to around freezing inside, but a rare occurrence.

Walls are 12 ft high, about 50-50 concrete-wood framing. You can see R-26 blown-in walls. I’ve read here that fluff need to be closed in to be effective.

While I would like to put up foamboard, the fire-rated stuff is very expensive and usually special order. Would a vapor barrier, such as Tyvek work? I see Tyvek is Class A fire rated, which I think means it’s as good as you can get for a wallcovering. They make Tyvek FireCurb in Europe. It’s self-extinguishing with other fire features.

Also, notice the bare steel I-beams at top of walls. No insulation at all. I’m thinking I should wedge some foamboard into the beams. Would this be best? Thanks.

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  1. GBA Editor
    Kiley Jacques | | #1

    I'm giving your question a bump for experts to address. One thing I feel confident in saying is that your idea to "cut and cobble" foamboard at the top of the walls is a sound one in terms of an air-sealing strategy.

  2. Bruce_Davis | | #2

    Now that the holidays are over, maybe I'll get better results. Thanks.

  3. Expert Member


    The foam needs either an ignition or a thermal barrier base din its location:

    I don't see anywhere in Tyvek's literature any testing or approval as either.

  4. Bruce_Davis | | #4

    From the Tyvek FAQs. Guess I'm confused, here Tyvek seems to indicate not flame retardant but also says it has a Class A rating. Is this contradictory?

    Q16: Is Tyvek® flame retardant? What is its melting point and ignition point?

    A: Tyvek® should not be considered as flame retardant and its flammability is like most synthetic fibers. Tyvek® type 10 has been tested according to ASTM E84-89a with a class A rating. Type 14 Tyvek® has been tested according to 16 CFR 1610 with a class 1 rating. The melting point of Tyvek® is 135°C and the ignition point of high density polyethylene is approximately 400°C. Specific flame-retardant requirements can be met by applying a special coating to Tyvek®.

    1. Expert Member
      MALCOLM TAYLOR | | #5


      I would suggest contacting Dupont to clear up the confusion. However as this is a common situation, and Tyvek is never brought up as a solution, nor does Dupont advertise it as such, I think the chances aren't very good.

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