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  1. #1
    Join Date
    Mar 2009
    Posts
    238

    Default Bath fan vent kit for flat roof

    I recently bought a bath fan but the only vent kits i can find are for direct venting through a wall or a sloped roof but i have a flat roof. In this 1920s home where the exterior brick walls support the roof joists, im afraid to cut out an opening for the 4" vent line if i were to direct vent through the wall since the hold would be within inches under the joists supporting the flat roof. I figured my safest option would be vent straight up through the rood but im not sure if there is a special type of vent cap i need. Can someone point me in the right direction or am i just being paranoid about making a hole through the brick instead?
    My advice and opinions come from hands on knowledge...and This Old House Hidden Content

  2. #2
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,736

    Default Re: Bath fan vent kit for flat roof

    First, are you sure you have a 4" vent on this bathroom fan?

    Ideally you want to vent through the roof. You need to use flashing on the roof and cap the vent with a cap that reflects water.

  3. #3
    Join Date
    Jan 2010
    Location
    Northern Virginia
    Posts
    1,204

    Default Re: Bath fan vent kit for flat roof

    A 4" hole in a flat roof has the potential to allow a lot of rainwater to get inside if the flashing system has the least amount of defect. The wall vent has no risk, if a bit more work to get through.
    Casey
    Remove not the ancient landmark, which your fathers have set.

  4. #4
    Join Date
    Mar 2009
    Posts
    238

    Default Re: Bath fan vent kit for flat roof

    Yes it is a 4inch vent. Nutone QTN80E. I would rather not go through the roof but its it structurally safe to make a hole that big right under 2 roof joists?
    My advice and opinions come from hands on knowledge...and This Old House Hidden Content

  5. #5
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: Bath fan vent kit for flat roof

    Quote Originally Posted by dcalabro View Post
    Yes it is a 4inch vent. Nutone QTN80E. I would rather not go through the roof but its it structurally safe to make a hole that big right under 2 roof joists?
    I'm with Casey --- avoid going through the roof. Any pentration in the roof is a huge potentioal for leaks.
    A 4 inch hole isn't going to compromise the structure.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  6. #6
    Join Date
    Dec 2011
    Posts
    1

    Default Re: Bath fan vent kit for flat roof

    i just replaced my bathroom cieling exhaust fan. problem is that the old sheetmetal ... I a installing a panasonic bath fan in my upstairs bath,I have a flat roof with fairly ..... There's a roof vent kit marketed by Broan that uses 2-ply metallic laminate

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