Supply (& DWV) lines in exterior walls

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by DavidTu, May 28, 2010.

  1. DavidTu

    DavidTu Member

    Messages:
    237
    Location:
    Seattle, WA
    Perhaps Terry is best one to answer this one as I'm in Seattle so he knows the weather.... I'm wondering if it is acceptable to run supply lines in an exterior wall? (We'd be able to insulate.) As none of the bath's interior walls are shared w/ the downstairs (large open kitchen area) my other choice would seem to be to run up to attic and back down. What's best?


    (For sure I'd have to run the drains down the exterior... I assume that is fine?)
  2. shacko

    shacko Master Plumber-Gas Fitter

    Messages:
    561
    Location:
    Rosedale, Md
    The trouble with questions like this is all your answers have to be comfirmed by your local jurisdiction.

    A lot of areas will allow supply lines on exterior walls, but they require insulation on the outer wall and none on the pipe, the pipe has to be run as close a possible to the inner wall.

    Most attics are cold areas, not a good idea to run water pipe in there.

    Drains run on the exterior are usually not permitted, like I said you have to ask locally, sorry. :(
  3. DavidTu

    DavidTu Member

    Messages:
    237
    Location:
    Seattle, WA
    Does that mean you cannot have a fixture on the exterior wall (i.e. drop down wall to floor level) or that you cannot have a stack on the exterior wall? (or both!?)

    (No insulation on pipe so that inside air can warm it, right?)
    Last edited: May 28, 2010
  4. Terry

    Terry Administrator Staff Member

    Messages:
    14,754
    Location:
    Bothell, Washington
    In Seattle you can do it.

    Just don't insulate the pipe in the wall, make sure the blanket of insulation is on the outside.
    If you put pipe insulation around the pipe in an outside wall, it will freeze quicker.
    It needs to get warmth from the inside of the home.

    Running pipes in an attic
    Don't put any insulation around the pipes.
    Remove all insulation below the pipe, and lay fiberglass batts over them.
    Between the ceiling joists on either side, lay two more batts, keeping space open below the pipes.
    The heat from the home must be able to get to the pipes, and then you trap it.
    A pipe in an uninsulated attic will freeze otherwise.

    If you change the pipes, then PEX would be good.

    Example of pipes in an attic.
    [​IMG]
    Last edited: May 29, 2010
  5. DavidTu

    DavidTu Member

    Messages:
    237
    Location:
    Seattle, WA
    Double check: You mean you can do both, right? (i.e. DWV and/or supply lines in outside walls)
  6. Terry

    Terry Administrator Staff Member

    Messages:
    14,754
    Location:
    Bothell, Washington
    In Seattle it never gets that cold.
    Surrounded by water on both sides, the Salish Sea (Puget Sound) to the West and Lake Washington to the East.
    Seattle plumbing code allows waste, vents and water in exterior walls.

    As always, during a cold snap you should open doors on exterior cabinets to allow warm air to the exterior walls that have plumbing ( kitchen sinks are a biggie)
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