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Thread: attached garage shop, vapor barieer or no

  1. #1
    Join Date
    Sep 2016
    Location
    Modesto, CA, USA
    Posts
    9,889

    attached garage shop, vapor barieer or no

    I am buying a house with an attached garage. there is nothing covering the sidewall studs. It is open to the rafters as well. Plan is to insulate and drywall the walls and flat ceiling. There is an existing drywalled wall between the main house and attached garage.
    Ten years ago they said every wall every time vapor barrier. Now some people say if unheated and no freezing no vapor barrier lets it dry out when needed. Pretty much everything I have read assumes snow and ice with humid summers. I have never seen condensation on wood or drywall inside.
    I have read different opinions if any of this should have a vapor barrier or not. It will never be heated or air conditioned. Cars will park inside as well as shop tools. Climate never gets below freezing, summers are hot and dry. No water in the garage no sinks, no laundry.
    Bil lD

  2. #2
    Join Date
    Feb 2008
    Location
    E TN, near Knoxville
    Posts
    12,298
    If you want information based on research instead of random opinions search google for:

    wall insulation osti.gov

    That will give you a PDF file with comprehensive recommendations for insulation and vapor barriers. I know it covers heated and cooled buildings and where to place the vapor barrier for different climates. Vapor barriers should be eliminated in some areas of the country (there is a map). I didn't check to see if it covers insulated walls without heating and cooling.

    BTW, OSTI is a part of the US Dept of Energy, Office of Scientific and Technical Information. (Before my Lovely Bride retired she was a manager there.)

    There is also a building research center at the Oak Ridge National Lab that will answer questions like yours. I used to know who to call there but you'll have to search if interested.

  3. #3
    Join Date
    Nov 2007
    Location
    Houston, Texas
    Posts
    274
    In my opinion, no vapor barrier, 5/8" Type "X" drywall on the 'attached' wall(s) and the ceiling, and a solid-core door leading to the house, preferably with a closer and no glass. All for fire considerations. YMMV
    Don't let it bring you down,
    It's only castles burning,
    Just find someone who's turning,
    And you will come around

    Neil Young (with a little bit of emphasis added by me)

    Board member, Gulf Coast Woodturners Association

  4. #4
    Join Date
    Sep 2016
    Location
    Modesto, CA, USA
    Posts
    9,889
    Thanks for the link John. So I will use a vapor barrier on the outside walls. It only gets omitted or moved in the damp south east states. They left Hawaii and Alaska off the map.
    I think I will leave it off the shared wall. If that has one it should be on the conditioned side anyway.
    Bill D.

  5. #5
    Join Date
    Mar 2003
    Location
    SE PA - Central Bucks County
    Posts
    65,694
    If your shop is going to be conditioned space, follow whatever the guidelines are for your specific geography for insulation and vapor barrier for conditioned space. (residential) What's normal where you are might be different than what's normal in other parts of North America.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  6. #6
    Join Date
    Jan 2019
    Location
    Fairbanks AK
    Posts
    1,566
    Quote Originally Posted by Jim Becker View Post
    If your shop is going to be conditioned space, follow whatever the guidelines are for your specific geography for insulation and vapor barrier for conditioned space. (residential) What's normal where you are might be different than what's normal in other parts of North America.
    Whay Jim said. Vapor barrier goes on the hot side of the wall. In Alaska, right under the drywall. In Miami, as close to the exterior siding as possible. In between I would follow code and not install any more vapor barrier than local code requires.

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