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  • MAXIMUM dwv slope?

    What is the max? I know the theory that solids will come out of the liquid if the slope is too much but what is too much? The IPC gives a minimum slope of 1/16 to 1/4 and shows a slope of up to 1/2" in 710.1 sizing table. As you increase the size, according to the table, you increase the DFU's each pipe size can handle but at some point it has to become a disadvantage to have such a steep slope.
    Buy cheap, buy twice.

  • #2
    Re: MAXIMUM dwv slope?

    This is an interesting topic and one thats been debated many times. The codes of course are looking for 1/4ipf to 1/2 ipf as a minimum pitch (1\16 also) but though it may be implied by some the code never says anything at all about a maximum pitch. Some inspectors will try to say that the pitch should be say 1\4 ipf in all cases but again you can't find that in the code's, either ipc or upc. There is some scientific basis to the theory of solids separation though. I have looked through some of my plumbing text books and have as of yet not found anything about maximum pitch in any of the either.
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    • #3
      Re: MAXIMUM dwv slope?

      ben, the upc.code for this is 708.0.

      it only address the minimum slope of 2% / 1/4'' per foot.

      4'' and larger may have 1% / 1/8'' per foot if it's first approved and there's a reason such as structural conditions or depth of sewer.


      it's always been a concern of water and waste separating. but look at a high rise building. also there are plenty of hill side homes where the building sewer pipe is running pretty much on the surface of the hillside at a slope
      + or - 45 degrees.

      i can tell you this. from my drain cleaning experience, too little slope is a stoppage, while too much slope is not. at least that's what i find first hand.

      rick.
      phoebe it is

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      • #4
        Re: MAXIMUM dwv slope?

        The only answer I've ever gotten to this question was from an inspector, he stated that you shouldn't exceed 1/8" /foot over the required pitch. (never been able to find it in the book either, so thats his word)
        For us the pitch is 1/4" for all drains 3" & under, 1/8" for anything 4" & over.
        The only thing we'd put a 1/2" pitch on is storm/roof drains.

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        • #5
          Re: MAXIMUM dwv slope?

          I asked the inspector that question one time. He replied with "How much fall does a vertical pipe have?"

          The biggest problem I see is when someone puts a great amount of fall from a 90 elbow. It looks like that pipe is going to jump out of the hub.
          Anyone can tear a man down, few can build one up.

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          • #6
            Re: MAXIMUM dwv slope?

            Many years ago, I worked in a very small town in northern Idaho. There was a lawyer's house on a hill and his sewer ran down at nearly a 45 degree angle. It would plug constantly about halfway down. No obstructions or breaks or anything. Always fun dragging the snake 'way down the hill and running extension cords to get to that middle cleanout.

            My vote would be, yes, the liquids can run away from the solids. I've always considered it better to run at normal grade, offset 45 degrees, then go back to normal grade than to try to grade the entire line by splitting the difference.

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            • #7
              Re: MAXIMUM dwv slope?

              Originally posted by Herk View Post
              My vote would be, yes, the liquids can run away from the solids. I've always considered it better to run at normal grade, offset 45 degrees, then go back to normal grade than to try to grade the entire line by splitting the difference.
              This would be the correct answer.

              It is better to turn with an 1/8 or 1/4 bend and get back to grade.

              It's the in between that causes trouble.

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              • #8
                Re: MAXIMUM dwv slope?

                There lies an irony.
                In my state, anything from 10' outside the foundation requires a "drain layers" license from the particular town you're in.
                I have yet to see any lateral outside that 10' point that maintains any semblence to minimum or uniform pitch.
                I had a soil stack relocation last year where the pitch was screaming back to the street from a house on a hill at over a 6" pitch.
                I had to sub the exterior drain work out, I stipulated a more "friendly" pitch with the excavator.
                The "drain layer" told me I was going overboard.

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                • #9
                  Re: MAXIMUM dwv slope?

                  Ok I'll bite...what's a 'drain layer license'?

                  And why are some of the street mains pitched at over 10%...the poop seems to be keeping up with the fluids there

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                  • #10
                    Re: MAXIMUM dwv slope?

                    Originally posted by plumberscrack View Post
                    Ok I'll bite...what's a 'drain layer license'?

                    And why are some of the street mains pitched at over 10%...the poop seems to be keeping up with the fluids there
                    i think the answer lies in the fact that a sewer in the street typically has more consistent flow and tends to keep things flowing.

                    we all know that low flow toilets do not push the waste more than 45' on a single flush. more on a good plastic system and less on an older rough cast system.

                    turds stop flowing when the owners not home. the water will continue with the waste high and dry.

                    rick.
                    phoebe it is

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                    • #11
                      Re: MAXIMUM dwv slope?

                      Originally posted by plumberscrack View Post
                      Ok I'll bite...what's a 'drain layer license'?

                      And why are some of the street mains pitched at over 10%...the poop seems to be keeping up with the fluids there
                      LOL, a guy gets bonded in that town...I could do it, but sure as hell not about to run around to every town I work in and go through this process over and over.
                      The drain @ 10' outside the home is inspected by the town engineering dept. and has to be 6" SDR.
                      Usually GC's & excavators have the license...it's worthwhile to go through the process for a large project like new construction, most plumbers won't bother.
                      The clincher is that those drains are usually rediculously underscrutinized compared to the homes plumbing.

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                      • #12
                        Re: MAXIMUM dwv slope?

                        I've never seen a vertical plug, (other than a frozen line). I've often pondered this question and never had an answer.... if vertical is ok, and 1/4"/foot is ok, where is the danger zone?
                        This is my reminder to myself that no good will ever come from discussing politics or religion with anyone, ever.

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                        • #13
                          Re: MAXIMUM dwv slope?

                          Originally posted by Ace Sewer View Post
                          I've never seen a vertical plug, (other than a frozen line). I've often pondered this question and never had an answer.... if vertical is ok, and 1/4"/foot is ok, where is the danger zone?
                          Code considers anything at 45 degrees and greater vertical.1/4ipf or 2% is required on three inch or smaller.So I would say anything greater than 2% and less than 45 degrees.This is just a theory of mine.

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