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Thread: bathtub branch size question

  1. #1
    DIY Member Zenman's Avatar
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    Default bathtub branch size question

    I have a question regarding the branch size for the bathtub. I have researched it and have found conflicting information both in books and on this forum. I'm under UPC and in the state of NJ. Attached is a plumbing riser that I submitted to the inspector.

    On the second floor bathtub, there is a 1.5 inch drain that has a 90 degree horizontal turn. Eventually when it meets up the lav branch (vanity sink) I was planning on upping it up to 2 inches.

    So my question is... is the 1.5 tub branch with the horizontal 90 (long sweep) acceptable?

    Any other comments or constructive criticisms are welcome.
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  2. #2
    DIY Member Zenman's Avatar
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    No takers?

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    Moderator & Master Plumber hj's Avatar
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    Default drain

    It is acceptable, but I would not do it that way, just so my customers did not have premature drain stoppages.

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    DIY Member Zenman's Avatar
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    Thanks for your reply HJ. I see in other threads you have recommended 2 inch as well. I am considering it, but the problem is that the particular joist bay where the 90 elbow will be is very narrow. (Also if a different joist bay were used, two 90 elbows would be needed.) So I only have 4 inches between the joists and part of the long sweep 90 elbow will have to be inside the bored out joist - which means a lager hole - and this is why I am hesitant. I will test and see what fits in some scrap lumber I have.

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    Master Plumber nhmaster's Avatar
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    If you must use a 90 get a long sweep.

  6. #6
    DIY Member Zenman's Avatar
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    Yes, it will be a long sweep 90.

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    DIY Member Zenman's Avatar
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    Default more info...

    It gets a little confusing with different codes, but I'm searching on UPC and found that a bathtub drain is rated 2 DFUs. A vertical 1 1/2 inch pipe is good for 2 DFUs, however a horizontal 1 1/2 inch pipe is only good for 1 DFU. Which tells me that a 1 1/2 inch horizontal branch line is too small for my bathtub (under UPC.)

    After a bit of more research I found that "The UPC requires at least a 2-inch drain immediately beyond the trap." This is regarding bathtubs and some other fixtures (ie kitchen sink with disposal and dishwasher). Source: Code Check: Plumbing, Redwood Kardon, et al.

    In order for me to be code compliant, it looks like I need to go with a 2 inch branch line.
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    Consultant cwhyu2's Avatar
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    1"1/2 is fine for a tub,what the code says is combined fixture units.
    The portant out let of a lav is 1"1/4 min pipe size is 1"1/4 .
    The P/O of a tub 1"1/2 so min pipe size 1"1/2
    the more fixture units the larger the pipe.
    Tub is 2 F/U here.1"1/2 pipe.

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    DIY Member Zenman's Avatar
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    Thanks cwhyu2. I guess what I don't understand is the UPC T7-5 chart specifically where it says only 1 F/U is allowed on a 1 1/2" horizontal pipe.

    Oh yeah, nice car you have there cwhyu2.... looks like a '69 Mustang. Back in the '80's I had a couple of Mustangs - a '66 coup and a '73 Mach I... fun cars.

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    Plunger/TurdPuncher kingsotall's Avatar
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    Aren't isometric drawings so much easier to get an understanding of the piping layout. Great riser submittal, guess the geeky plumber in me is showing.

  11. #11
    DIY Member Zenman's Avatar
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    As someone once said, a picture is worth a thousands words. I have a CAD background and drew it up fairly quickly on the computer. I have found that I can draw a picture to explain something much faster than using words.

    I'm not sure the plumbing inspector will actually look at the ISO before he comes to inspect, so that's why I figured I would ask questions here first. He is hard to get a hold of, so I have not had a chance to ask him what he thought. Also some inspectors just want to say Pass or Fail. Which I totally understand, since they are not paid to design my layout. So I really do appreciate everyone's input on this forum.

  12. #12
    Consultant cwhyu2's Avatar
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    Quote Originally Posted by Zenman View Post
    Thanks cwhyu2. I guess what I don't understand is the UPC T7-5 chart specifically where it says only 1 F/U is allowed on a 1 1/2" horizontal pipe.

    Oh yeah, nice car you have there cwhyu2.... looks like a '69 Mustang. Back in the '80's I had a couple of Mustangs - a '66 coup and a '73 Mach I... fun cars.
    Mach1,351W,4v,325hp,been modified some but mostly real.FMX auto.3.25to 1
    rear end,And it is a blast,Pony cars rock!

  13. #13
    Moderator & Master Plumber hj's Avatar
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    Default drain

    Sometimes it is a judgement call by the inspector. Here, many, if not most, above the ground tub wastes are 1 1/2" and some under the slab ones are also.

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