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3" or 4" lateral

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  • #16
    Re: 3" or 4" lateral

    Originally posted by PLUMBER RICK View Post
    bigger is not always better.

    definitely 3''. the 4'' will not self clean as well. you still have plenty of dfu to add a laundry and another full bath and kitchen.

    all will eventually plug if it's just a toilet and lav.

    i have 2 large condo buildings i take care of that had powder rooms/ toilet sink, separated by over 60' from the rest of the waste system. the piping is exposed in the garage ceiling. fall is perfect, pipe is new no hub camered line and the line is spotless.

    a powder room only does not generate enough grey water discharge to help push out the paper and #2.

    a shower, tub, laundry is what helps with washing the waste to city main.

    1.6 is low, 1.28 is crazy

    rick.
    Thanks, Rick.
    This is what I sent the general contractor yesterday afternoon.

    I know that it sounds counterintuitive to say that a 3" line would be more appropriate then a 4" line for the sewer lateral coming from the Guest House. There was a time when I would have argued for the larger line. When the law requiring toilets to flush using no more then 1.6 GPF took effect in the mid '90's, plumbers started noticing stoppages on sewer lines which had previously given satisfactory service. While the general public was complaining about toilets that wouldn't flush, plumbers were trying to fathom this other consequence of a well intentioned law designed to save potable water.
    The problem is called inadequate line carry. In other words, the new toilets might evacuate the solids from the bowl, but the amount of water used is so small that it can only carry the solids a fraction of the distance a 5 gallon or even 3.5 gallon flush toilet did. One of the ways to improve line carry is to decrease the diameter of the discharge pipe. This is especially important when dealing with a single rather then a battery of toilets. Though other fixtures also contribute to flow, they, too, have built in restrictions on their gallons per minute. When you add in the fact that this is a guest house, with intermittent usage, the possibilities of stoppages can be magnified. This is due to solids falling out of suspension, partially drying because of sporadic use and creating damns which can trap other solids. Add to this the strong possibility that the toilet used in the guest house will be a 1.3 GPH unit (the about to be enforced government standard), thus decreasing flow even more.
    A 3" pipe is no guarantee that a stoppage won't occur, but, with 3" there will be better line carry and wall scouring then with 4". I say this with the conviction of one who knows he will be held accountable if there is a problem down the line.

    Your experience with powder rooms
    situated out in the boonies mirrors mine. Lone potties that get sporadic use from a occasional maid or nanny doing #1 and using copious amounts of paper are a recipe for disaster. A friend who does a lot of commercial ti's in warehouses says his company started using 3" on single unit half baths situated off the main trunk line back in the late 90's because they were getting a rash of stoppages which they linked to the introduction of 1.6's wcs.
    Last edited by Plumbus; 03-01-2009, 11:10 AM.

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    • #17
      Re: 3" or 4" lateral

      Just my opinion,,,But i find more plugged lines when 3" pipe is used on two bathroom houses....
      Any thing here must be 4" outside.
      If you know the 3" pipe is going to stop up because it only has one toilet.
      Than a bigger line with less fall and slower flow should move it further,

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      • #18
        Re: 3" or 4" lateral

        This has been a very informative thread ! In the future ,In a similar situation,I'll opt.
        for 3". I ran a branch for 3 fixture guest bath with 4" last week. It's signed off and be pour a 1200 sq.Ft slab this week. Too late
        I can build anything You want , if you draw a picture of it , on the back of a big enough check .

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        • #19
          Re: 3" or 4" lateral

          I know a lot of you guys live in Cal.but tell me you tell a customer to hold the handle on a comode, to give it more water to make things work.

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          • #20
            Re: 3" or 4" lateral

            I'd use 4".

            The water runs along the lower invert of the pipe - 3" or 4" isn't that different. Code allows, with special permission, a grade of 1/8" per foot - but only on 4". Think of it as more of a sewer than a drain. 160' is a long line. I'd rather be cleaning a 4" line than a 3" line over a long distance. Sounds like a good place to use 2-way cleanouts.

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            • #21
              Re: 3" or 4" lateral

              There has been a tremendous amount of discussion about this issue on plumbing forums, and in the engineering publications. I am no engineer, and proclaim no special expertise... but my take on what I have read is that this is not a valid argument. There certainly is concern about the reduced total water flow causing carry problems, but I have not seem where pipe size enters in as a major factor.

              The debate will continue.

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              • #22
                Re: 3" or 4" lateral

                Originally posted by Herk View Post
                I'd use 4".

                The water runs along the lower invert of the pipe - 3" or 4" isn't that different. Code allows, with special permission, a grade of 1/8" per foot - but only on 4". Think of it as more of a sewer than a drain. 160' is a long line. I'd rather be cleaning a 4" line than a 3" line over a long distance. Sounds like a good place to use 2-way cleanouts.
                This makes the most sense to me. This magical "scouring" doesn't seem it would really occur after about the first 5'. Maybe less.

                Last class I took the inspector/trainer said they had abandoned hydraulic gradient theory.

                We'll never know until we start using clear pipe.

                Gotta' get to Vegas to check out that Union Building.

                J.C.

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                • #23
                  Re: 3" or 4" lateral

                  Originally posted by lovetheUSA View Post
                  There has been a tremendous amount of discussion about this issue on plumbing forums, and in the engineering publications. I am no engineer, and proclaim no special expertise... but my take on what I have read is that this is not a valid argument. There certainly is concern about the reduced total water flow causing carry problems, but I have not seem where pipe size enters in as a major factor.

                  The debate will continue.
                  Perhaps you're right. I think what is needed is a little less debate and a lot more research. I just spent 10 minutes to no avail searching for a questionnaire on problems with low flow fixtures I was sent recently from a plumbing engineer journal I subscribe to. I'll keep looking for it. Plus, I sent an email to John Koeller, P.E. Technical Advisor for the U.S.-Canadian Alliance for Water Efficiency (publishers of the HETs performance tests) as well as GreenPlumbers workshop instructor, asking if he has any data on the relationship between pipe size and line carry. I'll report back with any news.

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                  • #24
                    Re: 3" or 4" lateral

                    Mr. Koeller answered with the following:
                    http://www.allianceforwaterefficienc...-02-18-09.aspx

                    Seems he's already studied this problem. And, more research is on the way.




                    I guess I should have asked him instead of you guys in the first place. (;-)))
                    Last edited by Plumbus; 03-03-2009, 02:15 PM.

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