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Thread: roughing in for a toilet before concrete

  1. #1

    Default roughing in for a toilet before concrete

    We're getting ready to pour a concrete slab in our barn and I would like to "rough-in" for a toilet and sink for possible future use. There is water in the barn and I'll be trenching water lines to the stalls for automatic waterers. We're in Wisconsin, by the way.

    Is there a good diagram/guidelines available for my reference to know what I should do? I only have about a week before the concrete shows up and this was sort of a last-minute idea.

    Any help would be greatly appreciated!

    Bob

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Well, a toilet requires either a 3 or 4" drain pipe. If you use a 4", you can pour the concrete right up to the pipe, since you can use an internal fitting flange. If you use 3", you should put the flange on the outside (an option with 4"). Since it needs to fit around the pipe, you need to put a removeable sleeve around the pipe so that you can get the flange on later. The majority of toilets in the USA are 12" rough in. That means that the center of the drain from the FINISHED wall is 12". Better to be a little bigger than smaller, since when you go with the normally available alternatives, you end up with 10, or 14". You need a vent line for each device (sink and toilet). The drain for the sink is usually in the wall behind the sink. A sink drain line is often 1.5", but there is often a minimum size (2"?) if it is going to be under concrete. Make sure to use the right fittings so that things can be snaked, if it ever becomes necessary, and maintain the 1/4" per foot drop for the drains. The vent lines can be combined above the flood plane of the sink (nominally 42"), then goes up through the roof. Don't try to get the toilet flange at the 'right' height, just leave it long and cut it off when you do the finished floor. The flange is best installed on top of the finished floor.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3

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    Jim,

    Thanks very much for taking the time to reply. Am I able to combine the drain for the sink and the drain for the toilet together under the concrete? Also, because I am a novice, I was hoping to maybe find a good book, or website that has some pictures to help me visualize the layout and components required. I don't speak plumbing jargon very well

    Bob

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    In the Trades kordts's Avatar
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    If you don't speak or understand "plumber jargon" are you sure you want to do a job that requires "plumber jargon?"

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    Retired Defense Industry Engineer jadnashua's Avatar
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    I think that as long as the two are vented properly and you use the right fittings, yes, you can connect them together...the exact details, somebody else would have to tell you. There may be a specific order, one may need to be upstream from the other, but I can't say.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    DIY scratch-pad engineer leejosepho's Avatar
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    Will you be running the sewage line out to an existing septic tank and drain field, or to a new septic system of its own? I ask because of the depth and slope factors involved.

    Personally, I would bring a 4" line in to where you want the toilet, then elbow up for the flange. Then, I would use a 4" X 4" x 2" sanitary tee at the wall for a 2" vent pipe going up through the roof. At that point, your toilet will work and the sewage line will be vented to prevent any "burps" back into your toilet.

    To add the sink, I would place a 2" sanitary tee in the vent line just above the vent tee already in the sewage line, then I would run 2" pipe over a little way and elbow up to another 2" sanitary tee at the proper height for the sink drain, then run up another couple of feet before elbowing back over to yet one more 2" sanitary tee in the vent line. A professional might suggest something a little better, but all of that will work ... and for now, you only need to pour in the 4" line, the vent fitting (with a stub of pipe), and the elbow for the toilet flange.

  7. #7
    Homeowner geniescience's Avatar
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    Quote Originally Posted by rjblumii
    ..."rough-in" for a toilet and sink ...
    without commenting on the above posts, I'll just say that you need to figure out where the waste pipe will run to, and post a line drawing to show how you would connect the two wastes together (use big Wye's laid almost flat) and how you would bring in venting. Remember the slope of the drain lines. Lastly, just a reminder: no P trap in either of these drains for toilet and sink.

    david

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