Bath drain options

Discussion in 'Shower & Bathtub Forum & Blog' started by KH1978, Nov 26, 2013.

  1. KH1978

    KH1978 New Member

    Nov 26, 2013
    trying to finish the drain for a new tub I installed where there was a shower. My problem comes from the holes in the joist from the original 2" drain line. For the trap to be high enough for the sheetrock to go back, I would need to cut the hole about 1" higher than what is there, (see pic 1). This would put the size of the hole at or just above the max size hole that I can cut in the joist without compromising its strength. if I run it to the right, (pic 2) I would have to put in a 90 degree bend to send it back to the line that it was running to, just further down the line. I know that having turns in a drain is not the best, but I feel like this my be the only option, but I wanted to get other opinions. Also what size should the pipe be, 1.5" or 2". I can do either, but 1.5" is a smaller hole to put in the joist that already has a big hole through it. There is also an overall picture, (pic 3 ) that shows everything. Thanks for any help, and this site has helped me so much on this bath remodel.

    trap hitting hole.jpg trap to right.jpg overall.jpg
  2. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    Grade from the vent can be 1/4" per foot. The vent can be within 42" for 1.5" and 60" for 2"
    You you raise it too far up, it becomes an un-vented trap that can siphon. Proper grade is critical for the hydraulic performance that is intended.

    When drilling a joist, you need to leave 2" on the top and 2" on the bottom.

    The tub trap and trap arm can be 1.5" with 135 degrees of change. A 90 and a 45
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  4. johnfrwhipple

    johnfrwhipple BATHROOM DESIGN & BUILD for both Canada & the US

    Jul 20, 2009
    Design Work World Wide: Bathrooms Vancouver Area
    North Vancouver, BC
    Thank You Terry! Nice to see a plumber that actually knows the proper framing restrictions.

    This is a good example of what NOT to do with your floor joists.


    You might find that in order to place the tub exactly where it needs to go you will need to upgrade or change the framing. Make sure you plan this well and ideally incorporate the use of a structural engineer in the planning. Most time simple changes are all that is needed. If you need to sneak a new floor joist in from below you will find that clipping the corner a little makes it way easier.
  5. KH1978

    KH1978 New Member

    Nov 26, 2013
    Thanks for answering my questions.
    Terry, you said that grade from vent can be 1/4" per foot. Can it be more or less? the reason I ask, is that when I was testing the sinks, water started dripping out of the pipe where the shower was originally. I just had a towel stuffed in it, water flowed up the pipe and saturated the towel. Also when you say vent can be within 42" for 1.5" and 60" for 2", can it be more that that? If I have the trap go to the right like in pic #2, for about a foot to get away from the holes in the joist, I would have to use a 90 to send it back to the original direction where it would dump into a 2" pipe that is perpendicular. That pipe the runs to the vent pipe in the wall. Sorry if I don't know the correct terminology, I'm learning as I go.
    John, hope you had a clean pair of shorts handy when you opened the floor up and saw that, I know I would have needed them:)
    Thought I had most of these framing issues thought out, wasn't until fitting in the trap that I notice how high I had to cut the hole which led me to look up how much I could cut out before compromising strength. That joist frames part of the stair opening, so it carries more of a load than the others pictured.
    Thanks again.
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