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Garage Air Barrier Question

SeanRyan | Posted in General Questions on

Hey All,

Working through air sealing my garage which is an attached, drive under garage with living space above and to the side. I’ve read a bit and watched Jake Bruton’s video (https://www.youtube.com/watch?v=JaiJH0HXf-g) on air sealing, but just trying to think through a couple details. Electric service is in the garage, so all electric will travel through the garage and poke through this air barrier. HVAC ducts will come from the basement side, and travel through the ceiling cavity that exists isolated from the garage.

Attached is a rough sketched blueprint of what we have going on with my current plan. Also attached is the current bearing wall that separates the garage that I worked on tonight. And as an FYI all will be covered with the necessary Type X fire rated drywall after air sealing is figured out.

The questions:
– In the above video, it seems like he’s putting interior zip on all four walls. In my mind, wouldn’t you only need interior zip on the walls that share a common wall with living space? So in my situation, the ceiling and bearing wall next to the basement? I guess maybe the idea, and risk, would be that noxious fumes could get up through the top plate transition of the other two walls, perhaps?
– I’ll be implementing the one penetration = one object. In a lot of the videos seen, that penetration seems to be happening when crossing through the connecting wall. But, with the use of floor joists for this project, could you consider the floor joist area above the garage an area that is part of the main house envelope? Ie. instead of worrying about crossing between the garage and basement wall, you seal all holes crossing between the garage and the garage ceiling… if that makes sense. So the ceiling directly above the electric service would be where you would make one penetration for each wire. 

Thanks!

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Replies

  1. Expert Member
    BILL WICHERS | | #1

    You're likely to be required by code to put up a layer of 5/8" drywall in that attached garage, due to fire resistance requirements. That drywall can (and should) then be detailed as your primary air barrier. That should make ductwork less of an issue, since it's likely to be entirely on the "living space" side of the drywall.

    For electrical penetrations, you can easily seal everything with canned foam -- just use the orange stuff rated for residential fire block applications (the "pro" cans of Great Stuff that go in the gun are this orange type of foam). Personally, I would try to put the electrical panel inside the house and not in the garage. Electrical panels will hold up much better over time if they're within the conditioned space. I strongly advise against garage-mounted electrical panels (and especially outdoor panels!) for this reason if there is any way possible way to avoid mounting them in those locations.

    Bill

  2. Expert Member
    DCcontrarian | | #2

    I agree with Bill that the Zip doesn't really serve any purpose. I also agree that moving the electrical panel into the conditioned basement makes everything simpler.

    You don't say what climate you're in, but in a cold climate you're going to want a vapor barrier on the warm side of your insulation. In the ceiling-floor space above the garage I would try to minimize ductwork to just what is needed for the room above, run it as close to the floor as possible and then put insulation in the space. Depending on your climate you might only need 10" of insulation, and the space looks pretty big so you might have a pretty good air space between the insulation and the floor.

    If possible, I would also detail the subfloor as an air barrier. For fire protection any holes should be filled with fireblock anyway. If the finish floor is wood the installer will probably put down rosin paper which will serve as an air barrier. You really don't want air leakage between the living space and the garage, both for comfort and safety.

    I like to cover the interior of a garage with plywood, over the drywall. That makes it easy to install hooks, shelves and cabinets. It also acts as something of a bang plate to protect the drywall from denting.

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