# Maximum recommended slope for a sewer line?



## glennac (Jan 25, 2018)

Minimum slopes are required by code for drain pipes depending on the size but not a maximum. Sewer lines however can have problems with steep slopes causing solids to be left behind during a flush. 

I understand that any slope over 45 degrees is safe to use but what would be the maximum slope you can safely use without having this problem? Especially if your using cast iron pipe in an office building in lieu of smooth wall PVC. 

The IPC doesn't address this issue. What do you all think? Thank you very much


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## rwh (Dec 17, 2014)

Maximum slope is 1:1. Or 12"/ft. Or 100% grade.


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## glennac (Jan 25, 2018)

Funny perhaps I wasn't clear enough in my OP. 

I have some specs from a plumbing engineer calling for a minimum slope of 1/8" and a maximum slope of 1/4" for a 4" sewer drain line. 

Now IMHO anything over a 1 to 1 slope or a 45 degree angle would be safe to use and all the solids would move down the pipe. 

My question is very clear. What would be the maximum slope for a cast iron pipe to have and avoid the problem of solids staying behind in a sewer line not counting of course a 1 to 1 slope and above? Does anyone have an opinion on this. Thank you very much.


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## GAN (Jul 10, 2012)

Illinois has minimum required slope for building drains, You can get slightly more DFU's with a greater pitch.

http://www.ilga.gov/commission/jcar/admincode/077/07700890ZZ9996ahR.html

http://www.ilga.gov/commission/jcar/admincode/077/07700890ZZ9996agR.html

Beyond this, I think you will find and old wives tail. More fall than listed the argument of water flowing away I have heard. That in mind the theory of the next wash moving things along is there. Now granted many sewer mains run at only 1% grade, very flat and they work with larger diameters. I have hand tapped clay mains running 20% or so, which then run so fast nothing slows them down, including a chisel dropped in the main. I have also installed clay sewers running down a hill and we sure as heck did not attempt to stay at 1/4" to 1/2" per foot fall. We got it heading downhill and let her rip until the bottom, then flattened it out again.

General accepted practice I think you will find 4" and greater at an 1/8" to 1/2" per foot. Nothing under 1/4" per foot on 2".

Here is a good UK article on this.>>> http://www.wyre.gov.uk/info/200316/building_control/166/basic_guide_to_calculating_falls_and_gradients_for_drainage

After all this, the smaller the size the more critical to stay within 1/8" to 1/2" per foot fall. When you get to 6" and larger which will tend to have much more of a volume of water going through it won't make a real difference. Only lower flow single family or businesses will see the effect.


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## Plumbus (Aug 4, 2008)

If your engineer specifies a maximum of 1/2"/ft, then that is what your limitation is. If site conditions appear to require greater fall, your only recourse (if you don't wish to expose yourself to litigation) is to present the powers that be with an RFI explaining your predicament and let them parse it out.


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## NyNick (Feb 14, 2013)

Einsteins theory of plumbtivity....4" ID = 1/8 per ft divided by the velocity of water x Poo to the second power. There is no maximum and minimum...4"ID gets pitched at 1/8 per foot. Below 4" gets pitched 1/4" per foot. Any more than 1/4 inch the water flows faster down the pipe than said Poo leaving it behind to slowly build up. This is most likely over a "straight" run of 100ft. To get back to your question though.the IPC does address this issue in 708.3.3. anything over 45 degrees is considered a change in direction. A cleanout must be installed at each change of direction. If you have more than one change of direction in a run than 1 cleanout is required for each 40ft of developed length. Go tell your architect to put that in his clip board and smoke it.


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