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Thread: 2-inch trap between 2x8s?

  1. #1
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    Default 2-inch trap between 2x8s?

    Russell from Madison WI here.
    I'm creating a master bath out of a bedroom and two closets in our 90-year-old Arts and Crafts hybrid. I'm doing a custom shower and need to put a 2-inch trap between the existing 2x8 joists (I have sistered and blocked them with 2x6s). The plumber I'm considering hiring for the rough-in says that I need to raise the shower floor by 3-inches (2 2x4s) to make it work. I really don't want to raise it. Any alternatives or is this the only way? Thanks in advance.

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    DIY scratch-pad engineer leejosepho's Avatar
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    I have 2x6 joists, and I simply put the trap a little farther on down the line rather than raising the tub/shower unit sitting under a 7'4" ceiling.

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    Homeowner geniescience's Avatar
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    Default 2 ways around this

    1. look at Oatey drains on their web site. Some of them have horizontal tailpieces; that takes the least space. It is as if the drain had a "flush elbow" sending the waste water 90 degrees over to the side.

    2. Also, a "street 90" is a small radius elbow that has one end male, and one end female; it takes less space when connecting into other fittings and into the drain itself than a regular elbow.

    All plumbers know about street elbows.

    I am presuming that the plumber wanted to raise the floor level so that he had space under the drain for the pipes. Ask him what he intended to do with all that space, before you discuss any of the above. He may surprise us with another answer.


    david

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    Quote Originally Posted by leejosepho
    I have 2x6 joists, and I simply put the trap a little farther on down the line rather than raising the tub/shower unit sitting under a 7'4" ceiling.
    Wouldn't that would be a running trap and not up to code?

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    Quote Originally Posted by geniescience
    1. look at Oatey drains on their web site.
    The only traps I saw were Bell traps. Those aren't legal most places, are they?

    Quote Originally Posted by geniescience
    2. Also, a "street 90" is a small radius elbow that has one end male, and one end female;
    I'm pretty sure that's what I tried. From the bottom of the joist space (plaster ceiling below), the trap came to the top of the 2x8.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Sounds to me like he is planning to put the liner on the floor. It needs to be a little above that since by code, the liner MUST be on a sloped floor. To get that, you build what is called a preslope. That needs to be at least a 1/2" or so above the subfloor at the drain, and more is a very good idea on a wood subfloor. A drain and trap should fit. If you want to verify the plans are right on how to build a shower, check out www.johnbridge.com . Read the article in their "Liberry" link. Very informative. There a lots of people that have been building showers for a long time that don't do it per code. Doesn't mean it will leak, but it won't give you the performance you are paying for...do some homework.
    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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    Well I'm TRYING to do my homework. I am planning on building the preslope myself. But there has to be a subfloor sitting on the joists though and the trap bend has to fit under it, so I'm still confused. This image from the John Bridge forums shows the trap bend fitting neatly in the joist space:

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    Retired Defense Industry Engineer jadnashua's Avatar
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    I've only dealt with a few, but they've fit in a 2x8 joist bay...it is tight, but it fits. My guess is it may depend somewhat on they brand of drain you use. The last one I did was with the Kerdi drain, and there was maybe an inch or two of space. This was with the lip of the drain about an inch above the subfloor (it was the Kerdi drain, which may differ from a clamping drain). You should try to get about an inch of deck mud at the drain on a wood subfloor. You can use less on a slab.
    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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    Forum Admin, Expert Plumber Terry's Avatar
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    The problem is if you try to drill and place the pipe through the joists.

    2" of wood needs to be on the top and the bottom, which works with a 10" joist.

    As long as you are not drilling the joist, but merely going between them, it could work perhaps.

    Did I just hedge my bet there?

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by flanneljammies
    Wouldn't that would be a running trap and not up to code?
    I do not know the term "running trap", but I do know what I have works just fine, and I would assume "code" would not go against that.

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    Homeowner geniescience's Avatar
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    Default Big Picture; where goes it?

    it is true that we are all missing information in The Big Picture that only the tread originator knows for sure.

    Once the pipe exits the P trap, where is it going to go? Between the joists, to... ? Or , ... ?

    The plumber on site also knows.

    David

  12. #12
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    Yes, between the joists to tie in with the tub drain. It looks to me like I should only really need to raise the floor by 3/4". I've got a couple of other plumbers to evaluate the rough in. Stay tuned...

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