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Thread: Offset Toilet Flange or Header Joists and Relocate Toilet Drain?

  1. #1
    DIY Junior Member sprusgoose's Avatar
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    Feb 2012
    Vancouver, B.C.

    Default Offset Toilet Flange or Header Joists and Relocate Toilet Drain?

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    I am about to get started on a bathroom reno that I put on hold from last year and need to re-jig the layout a bit to fit in a shower. The dimensions of the bathroom are 63"x69". Currently the back of the toilet sits against the 69" wall and it will need to be turned 90 degrees to give me clearance on the 63" wall for a 32"x32" shower. Unfortunately, there is a joist running at exactly 15" on center from the wall when the toilet is turned 90 degrees, and as I have no wiggle room in order to get the shower in with proper clearance for the toilet, I need some advice on what the best solution to the problem is.

    I currently have 3 1/4" from the center of the toilet drain (3" ABS) to the joist in question (12" from center to the wall). The way I see it, I can either:

    1) shift the toilet drain over 1", and then get an offset toilet flange to make up the last 2", or,

    2)I can header the joists and move the toilet drain over the full 3".

    I'd prefer to do option 2 as I have a drop ceiling in the room below (a bit of drywall around the bulkhead the currently houses the toilet drain off the main stack), however, previous to when I bought the house, someone has run all sorts of electrical through and under the joists that would have to be pulled from the panel and re-routed as it currently interferes with where I'd have to place headers. Is option 1 acceptable? It would require that my toilet drain rough-in be 2-2 1/4" from the joist...is this too tight (any code for this??)? Any help is appreciated!
    Last edited by Terry; 11-30-2013 at 11:22 AM.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Sep 2004
    New England


    NOt all offset toilet drains are created equal...some are not all that bad to use, some are a constant clog waiting to happen. They should be avoided, if possible. If you use one, you want one that goes down at an angle, not a much shallower design that looks more like a spoon.

    Code has some fairly specific rules about notches and holes through joists...plumbers tend to ignore them, but the structural guys may force the issue, if they are called in, too. Basically it is not okay to notch a joist...similar to an I-beam or a truss, it is the top and bottom that provide the strength - the middle (often hollow on trusses with a web) is just there to hold the top and bottom pieces in proper position for tension and compression for support.

    It's hard for me to follow exactly what you want to do, but if I were doing it, I'd rather not use an offset flange and would either consider a different rough-in toilet (10 or 14") if I couldn't redo some of the framing to make a standard 12" one work. Keep in mind, if it isn't 12", your choice on toilets goes way down, and you may not be able to reuse your existing one, if that was in the plan.

    A sketch may help. There is no issue with the flange being against a joist (i.e., there is no requirement for there to be a gap), but you do want to avoid notching things. A notch effectively makes the entire joist the equivalent of its remaining height. Whether that is still sufficient, you'd have to run the span tables, but most places don't overbuild much.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Forum Admin, Expert Plumber Terry's Avatar
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    Aug 2004
    Bothell, Washington
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    The toilet needs 30" of space. 15" to center on both sides. That's for your shoulders and arms.

    A 32" shower, no longer code anymore, requires a wall normally on the sides. That's going to take up some space.
    Most Neo Angle showers are 38", but don't require a wall.

    Offsets 1.5"

    A closet flange with built in 45 degree angle.

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