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Thread: shower remodel on slab

  1. #1

    Default shower remodel on slab

    hello - this is my first post, I just wanted to say thanks to all for the great site and advice.

    I am putting in a basement bathroom designed primarily for my mother-in-law's use. For that reason, I want to use a walk in shower instead of a tub. Unfortuantely, the stub-in is 1-1/2" as I am sure you all guessed. From the other threads, I understand that the shower requires a 2" drain and trap. Here is my concern - what is the risk of cracking the other pipes in the slab as I jack-hammer to get access to the existing trap? The water line in the trap is one-foot below the surface of the slab, so I am going to have plenty of material to remove.

    To be honest, I still haven't figured out the 2" requirement per UPC. I think that IPC only requires 1-1/2". Seems counterintutive when you see showers with 4 body massage nozzes, a rainmaker, and handheld shower all on a 2" drain, but a regular old-fashioned shower requires the same 2".


  2. #2
    DIY Senior Member finnegan's Avatar
    Join Date
    Aug 2005


    I NJ you need 2" for a shower. The theory is that the curb will hold less water than a tub, so you need to drain faster. However, I have seen 1.5" shower drains that work just fine. If your work is not gonig to be inspected, I would stick with the 1.5". If it is going to be inspected, you can try bouncing it off your inspector first and see what he says before breaking the slab. You never know.

  3. #3


    I've heard of some cases where the plumbing was actually 2" but reduced at the end to accomodate the tub drain. if you do decide to get the hammer, try chipping carefully around the drain pipe to see if you find 2" stuff a few inches down. If you do, run down to the store and buy a lottery ticket.

  4. #4
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default drain

    I would say in most cases the pipe to the tub is going to be 2" unless the plumber who installed it was really trying to do the cheapest, least code compliant, installation, so your lottery chances are the same as anyone else's. With a curbless shower you have about "zero" water retention capacity so unless the drain is as large as possible you could have water running out onto the floor either after a long shower or when a little soap and hair start to slow the drainage down.

  5. #5
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    San Diego


    For a walk-in, you do not want to compromise the drain.

    You said the stub in is 1, but are you sure that the pipes underslab are not already 2"? Maybe you only need to change a santee or a trap. Most places would not put any 1 under the slab.

    Anyway, do it right or granny will be throwing rooster tails off the wheels of her power chair!


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