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Community and Q&A

Is fiberboard air impermeable?

Rachel Wagner | Posted in GBA Pro Help on

A recent GBA post noted that some builders are finding that OSB isn’t always air impermeable. I’d like to know if fiberboard, such as Biltrite or BraceRite, is air impermeable. Specifically, I’m interested in trying to use it as an air barrier, in an assembly where I need the sheathing to be able to dry, and fiberboard has a permeability of around 20. But can it be an air barrier, if I tape or otherwise seal the seams? I can’t find this info on the company’s website or anywhere else I’ve been looking.

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Replies

  1. Rachel Wagner | | #1

    Ummm, I wrote the question too hastily. The GBA article answers it for me: https://www.greenbuildingadvisor.com/blogs/dept/musings/osb-airtight
    No, asphalt-impregnated fiberboard does not meet the test to qualify as an air barrier.
    http://www.cmhc.ca/publications/en/rh-pr/tech/98109.htm

  2. Rachel Wagner | | #2

    I followed my question to GBA with a query to International Bildrite, a manufacturer of fiberboard sheathing, and a rep called me. He is now looking into any testing that may have been done on coated fiberboard, to see if any of their products might meet the .02 air permeance testing threshold suggested by the Canadian research (note, that CMHC publication was from 1989). I'll write more if there is more to share once I hear back from Bildrite.

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