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Stud spaces as air ducts

user-1137156 | Posted in Building Code Questions on

Are there any code issues with using the stud spaces of interior walls (dry walled) as forced air ducts?

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  1. GBA Editor
    Martin Holladay | | #1

    According to the 2009 IRC, Section M1601.1.1:
    "Stud wall cavities and the spaces between solid floor joists to be used as air plenums shall comply with the following conditions:
    7.1. These cavities or spaces shall not be used as a plenum for supply air.
    7.2. These cavities or spaces shall not be part of a required fire-resistance-rated assembly.
    7.3. Stud wall cavities shall not convey air from more than one floor level.
    7.4. Stud wall cavities and joist-space plenums shall be isolated from adjacent concealed spaces by tight-fitting fire blocking in accordance with Section R602.8."

    So -- you can't deliver supply air that way, but you can pull return air through stud spaces.

    I think it's a stupid idea, however. Use metal ductwork, and seal the seams with mastic.

  2. user-1137156 | | #2

    Thank you!
    This will require a bit of a change to my mini split in a closet+ air handler way of hiding the indoor unit. To be compliant I'll use a down flow air handler pushing air into metal ducts through the basement as the "supply" side with metal ducts all the way to the registers and the return path using stud spaces and my ceiling "service cavity" ending in grill work in the ceiling and wall above the door of the closet above the mini split. I doubt that a whole basement used as a "return plenum" could be compliant with 7.4.

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