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Community and Q&A

Should foam insulation in band joists be separated from living area by drywall?

Hallie Bowie | Posted in Energy Efficiency and Durability on

There is lots of talk about using foam to insulate and seal the band joist area. It’s my understanding that foam insulation, either spray or most rigid forms, is not intended to be left exposed to living spaces. I’ve always understood that it should be covered by drywall, which is more flame resistant and not apt to emit toxic fumes when it comes into contact with fire. But even the GBA detail for an existing band joist insulation retrofit with rigid foam does not show any covering over the foam, or indicate that the foam used had a fire resistant coating.

Is there a reason this is not a concern?
Hallie M. Bowie, architect
New Leaf Home Design

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  1. Daniel Glickman | | #1

    The Code requires it clearly. Not always is it enforced.
    Daniel Glickman
    Sustainable Construction Services, Sherborn MA

  2. GBA Editor
    Martin Holladay | | #2

    Which code are you referring to?

    The 2006 International Residential Code allows (in Section R314.5.11) the use of foam insulation at rim joists without the protection of a thermal barrier, as long as it it no more than 3.25 inches thick, it has a density of 1.5 to 2.0 pounds per cubic foot, and as long as it meets certain flame spread index requirements and smoke developed index requirements.

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