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Thread: Shower Drain Size and Code

  1. #1
    DIY Junior Member centurion's Avatar
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    Default Shower Drain Size and Code

    Have seen many references that a shower drain needs to be 2". Here in NJ they follow 2009 NSPC which in 7.10.4 says "for a shower with single shower head, the waste outlet connection shall be no less than 1-1/2" ". What am I missing?

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    In the Trades liquidplumber's Avatar
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    The code book is a wonderful thing. On one page it says one thing and on the next page it says something totally different. And just to make it interesting, the inspector will have a 3rd totally different interpretation of the code. Basically, to answer your question, somewhere in the code is an "exception" or a footnote or a comment or a drawing that will inform you that 1 1/2 drain is fine if youre talking about a tub/shower with single shower head.... but a shower stall would require the 2 inch drain.
    The code book is not designed to be user friendly. There are codes that plumbers must abide by that are in other trades code books as well. Imagine plumbers having to follow rules that are in the HVAC or electricians code book. it happens everyday. Sometimes its amazing that anything ever gets done..lol

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    DIY Junior Member centurion's Avatar
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    Quote Originally Posted by liquidplumber View Post
    The code book is a wonderful thing. On one page it says one thing and on the next page it says something totally different. And just to make it interesting, the inspector will have a 3rd totally different interpretation of the code. Basically, to answer your question, somewhere in the code is an "exception" or a footnote or a comment or a drawing that will inform you that 1 1/2 drain is fine if youre talking about a tub/shower with single shower head.... but a shower stall would require the 2 inch drain.
    The code book is not designed to be user friendly. There are codes that plumbers must abide by that are in other trades code books as well. Imagine plumbers having to follow rules that are in the HVAC or electricians code book. it happens everyday. Sometimes its amazing that anything ever gets done..lol
    Understood. But what I quoted specifically refers to a shower. I will ask the inspector, but unfortunately in our town he is part time and not quickly reachable, so I was trying to see if someone here had any first hand experience in NJ.

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    In the Trades liquidplumber's Avatar
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    Quote Originally Posted by centurion View Post
    Understood. But what I quoted specifically refers to a shower. I will ask the inspector, but unfortunately in our town he is part time and not quickly reachable, so I was trying to see if someone here had any first hand experience in NJ.
    Youre not understanding what im saying. you may read something on one page that says you may do something, and then on another page it says you shall not.
    You cant take one little reference and assume that its all good. trust me on this, the inspectors know exactly where the you shall not do that section is AFTER you've done it wrong.
    Agreed that I dont know NJ codes, but whats the aversion to using a 2 inch trap on a shower? Ive seen 1 1/2 shower drains here done by homeowners and handymen so yes it will work.. but it will work and its done right are 2 different things. In the end if your inspection jurisdiction will allow you to do it, and you really want to do it, then just do it.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The codes are written for the 'what if' situations after lots of experience...they sometimes change as new materials and experience dictates. The shower drains all used to be 1.5", and there's a lot of them still out there, working okay. But, they found that some 'what if' situations could be bypassed if it was increased to a 2" pipe, so that's what the new codes generally require. A tub with a shower, is still a tub, and 1.5" works since it has an overflow and a lot more room for water storage before it can overflow a curb and into the room.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the Trades liquidplumber's Avatar
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    Quote Originally Posted by jadnashua View Post
    A tub with a shower, is still a tub, and 1.5" works since it has an overflow and a lot more room for water storage before it can overflow a curb and into the room.
    Ding ding ding...... we have a winner!..... that is exactly right.

  7. #7
    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Up here in Canada we have smaller water particles that move faster because of the cold! So a 1 1/2" PTrap and waste line works well enough.

    Personally I prefer 2" lines for the safety and ease of use but I have tested many 1 1/2" shower drain lines over 18 GPM with good results. I have found that once you bridge about 5-8 GPM the water level will rise about a 1/4" above the drain. At 7-10 GPM there is about 1/2" of water above the drain. And 10-15 GPM sees about 5/8" of water above the drain.

    A 2" line preforms better of course but even a 2" drain with plenty of water will build up some.

    A typical shower head delivers 2.5 GPM at that rate a 1 1/2" drain line can more than handle the water flow.


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    Quote Originally Posted by centurion View Post
    Have seen many references that a shower drain needs to be 2". Here in NJ they follow 2009 NSPC which in 7.10.4 says "for a shower with single shower head, the waste outlet connection shall be no less than 1-1/2" ". What am I missing?

    Your code allows for a 1.5" trap and 1.5" drain for a shower stall with a single showerhead. Rock with it.....perfectly legal.

  9. #9
    DIYer, not in the trades LLigetfa's Avatar
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    Quote Originally Posted by johnfrwhipple View Post
    Up here in Canada we have smaller water particles that move faster because of the cold! So a 1 1/2" PTrap and waste line works well enough...
    It gets much colder in this part of Canada so the water particles expand as they reach the freezing point. My inspector insisted on 2" lines even though the tub drain's tailpiece is smaller. I wish the wife's soaker tub had a 2" tailpiece to match so she'd stop complaining about it slow draining.

  10. #10
    DIY Junior Member centurion's Avatar
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    Thanks to everyone that responded. I especially enjoyed the information about water particle size and speed. Seriously, I totally understand that code in minimum and why 2" is preferred. I was just trying to find where in the code it says 2", because the only reference I could find was 1.5". I think we have beat this one up enough. Thanks everyone.

  11. #11
    Moderator & Master Plumber hj's Avatar
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    If you interpret the code literally, then the shower WILL have a 2" drain outlet, and to use 1 1/2" piping you would have to "reduce the size in the direction of flow" which is NOT permitted.
    Licensed residential and commercial plumber

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    Quote Originally Posted by hj View Post
    If you interpret the code literally, then the shower WILL have a 2" drain outlet, and to use 1 1/2" piping you would have to "reduce the size in the direction of flow" which is NOT permitted.
    HJ,I pulled up a copy of their code. It says the drain can be 1.5" for a stand up shower with a single showerhead. You can buy shower drains that have a 1.5" outlets.

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    Moderator & Master Plumber hj's Avatar
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    qutoe; You can buy shower drains that have a 1.5" outlets.

    What you should say is that they "make" 1 1/2" shower drains, because I have never seen one to purchase it. And, just because you "can do it" does not make it a good idea.
    Licensed residential and commercial plumber

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    Quote Originally Posted by hj View Post
    qutoe; You can buy shower drains that have a 1.5" outlets.

    What you should say is that they "make" 1 1/2" shower drains, because I have never seen one to purchase it. And, just because you "can do it" does not make it a good idea.
    Say it any way you want,the drains can be purchased by anyone who wants to buy it. The original posters code allows for the installation of 1.5" shower traps and drains for a single head stand up shower.

    So his DIY question has been answered.

  15. #15
    ACO Shower Drain Sales johnfrwhipple's Avatar
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    I've never seen a 1.5" Shower drain.

    Most times we set in a 2"-1.5" bushing or go with a 2" piece of pipe and a 2"x1.5" MJ No-Hub fitting.

    JW


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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