How much of a fall per 50′ or 100′ of main sewer line from house?

Home Forums Public Forums Drainage & Sewerage How much of a fall per 50′ or 100′ of main sewer line from house?

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    • #279463
      Douglas Hill

      I’d just like to know what the measurement would be on a 4″ diameter sewer line. Any help is appreciated. Thanks!

    • #300933
      Retired plbg1

      Sometimes you use 1/8″ per ft.
      1/4″ per ft. usuallt the eng. has the grades on plan. But if you are doing it yourself you can buy a grade level are make one. You also can fig. 1″ fall to 10′, if really depends on where you come out of house and where you connect, best way for you is to dig at start and go to connection and then lay the pipe.

      Art retired plbg

    • #300934

      the fall for 4 inch sewer line is one foot in sixty feet

    • #300935
      John Aldrich1

      jason_m, the very minimum slope for 4-inch diameter sewer pipe required in most codes and regulations is 1/8-inch per foot. That is 1-inch of fall for every 8-feet of run. The recommended or ideal slope is 1/4-inch per foot or 1-inch of fall for every 4-feet of run. It is not a problem if the slope of the sewer pipe is greater than 1/4-inch per foot.

      So to answer your question:

      50-feet @ 1/8-inch per foot = 6 1/4 inches
      50-feet @ 1/4-inch per foot = 12 1/5 inches

      100-feet @ 1/8-inch per foot = 12 1/2 inches
      100-feet @ 1/4-inch per foot = 25 inches

    • #300936

      Thank you very much for the replies!

    • #300937

      I just wanted to call attention to the per-foot drop rate having a recommended upper limit of 1/4″. We all know that if the drain doesn’t have ENOUGH slope waste won’t flow. Apparently if there is TOO MUCH slope, say 2″ per foot, solids and liquids will start to separate and you’ll develop islands of solid waste that could eventually lead to blockages. This of course doesn’t preclude really high slopes, like verticals and 45 degrees, but in those “low but high” sloped “horizontal” runs the problem is real.


    • #300938
      John Aldrich1

      NtP, I respectfully disagree with your premise regarding excessive slope in PVC sewer pipelines. In my 29 years of experience of installing hundreds of 4-inch PVC sewer pipelines that exceed the recommended 1/4-inch per foot slope in the Rocky Mountains of Colorado, I have never experienced this problem. The problem may occur when the pipeline is very old and rough cast iron or disintegrating Orangeburg pipe, but I do not believe that the problem will occur when using 4-inch PVC pipe. At least, that has been my experience.

      There are situations where it is impossible or impractical to install a sewer pipeline with the “recommended” 1/4 inch per foot slope.

    • #300939


      I think you’re right about it not being a real problem with slick plastic pipe walls. The separation of solids from liquids can be a problem with cast iron, which has a rougher surface. I was just passing on what I was told years ago when all the drain/sewer pipe was either clay or cast iron, where the rougher surface and greater friction can lead to the separation of solids and liquids during long horizontal runs.


    • #300940
      Retired plbg1

      I dug up pipe that was flat and also ones that had lots of fall and they worked for as long as 40 yrs. are more, so realy its hard to describe the fall, realy the best way would be to see a plumbing system for toilets and other fix. run in glass pipe as a modular in a building where you could see all the action with no fall to a lot of fall.

      Art retired plbg

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