# Maximum slope of building sewer?



## Plumbus (Aug 4, 2008)

House on a hill, 400'+ from the street lateral. GC wants to horizontal drill sewer line. His question to me: If minimum slope is 2%, what is the maximum slope? Because of the slope of the hill, some of the grades between clean outs (100') could be as great or greater than 20%. My 2007 CPC does not address the issue. My experience is that it doesn't matter. But, I told him I'd ask for 2nd opinions.


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## user4 (Jun 12, 2008)

Too much pitch combined with 1.6 GPF toilets = lots of soft blockages of the sewer.

That is not from any code, just a personal observation. If you do install this with radical pitch I would recommend putting in a CO at the tie in to the main that you can jet in both directions from.


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## 22rifle (Jun 14, 2008)

Too much pitch combined with 1.6 GPF toilets *plus an over sized sewer* = lots of soft blockages of the sewer.


There, fixed. In my opinion anyways.


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## ILPlumber (Jun 17, 2008)

22rifle said:


> Too much pitch combined with 1.6 GPF toilets *plus an over sized sewer* = lots of soft blockages of the sewer.
> 
> 
> There, fixed. In my opinion anyways.


:thumbsup: Lotta codes still figure DFU's based on the old big flushers.

I read in PE one time that too much slope is a myth. I'm no drain cleaner though. Proofs in the puddin:laughing: pun intended


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## user4 (Jun 12, 2008)

22rifle said:


> Too much pitch combined with 1.6 GPF toilets *plus an over sized sewer* = lots of soft blockages of the sewer.
> 
> 
> There, fixed. In my opinion anyways.


Our code calls for a minimum 6" once it leaves the building.


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## Plumbus (Aug 4, 2008)

Killertoiletspider said:


> Our code calls for a minimum 6" once it leaves the building.


Fortunately, ours doesn't. The two way CO is a good idea, thanks.


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## service guy (Jun 26, 2008)

There is no maximum pitch here. Only minimum. I have installed sewers and drains with a very strong pitch and they never had any problems. Of course, back-pitch or not enough pitch causes huge stoppage problems.


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## 22rifle (Jun 14, 2008)

Killertoiletspider said:


> Our code calls for a minimum 6" once it leaves the building.


I knew that. 6" CI and one or two 1.6 toilets? I would be running it right on grade myself.

4" PVC and the same toilets? Completely different story in my opinion.


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## Plumberman (Jul 7, 2008)

1/4 per foot on 4". Standard Plumbing Code.


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## user4 (Jun 12, 2008)

22rifle said:


> I knew that. 6" CI and one or two 1.6 toilets? I would be running it right on grade myself.
> 
> 4" PVC and the same toilets? Completely different story in my opinion.


Our code doesn't allow PVC sewers either, it is all clay or cast iron.


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## Plumberman (Jul 7, 2008)

Killertoiletspider said:


> Our code doesn't allow PVC sewers either, it is all clay or cast iron.


Just curious... What are the city mains run in?


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## user4 (Jun 12, 2008)

Plumberman said:


> Just curious... What are the city mains run in?



24" and under are run in clay, over twenty four inch are either brick or concrete, depending on whether they have been replaced or not. Anything over 60" is relatively new, and is concrete.


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## Ron (Jun 12, 2008)

service guy said:


> There is no maximum pitch here. Only minimum. I have installed sewers and drains with a very strong pitch and they never had any problems. Of course, back-pitch or not enough pitch causes huge stoppage problems.


All so true, we live in a place that houses are up in the hills, and I can tell you it's a myth that too much slope leaves sewage behind. Min pitch 1/4" per ft but it can have 1/8" per ft is grade is not happening at 1/4"


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## Plumberman (Jul 7, 2008)

Killertoiletspider said:


> 24" and under are run in clay, over twenty four inch are either brick or concrete, depending on whether they have been replaced or not. Anything over 60" is relatively new, and is concrete.


Got ya.... Thats some big a clay!


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## user4 (Jun 12, 2008)

Plumberman said:


> Got ya.... Thats some big a clay!


Chicago is a big  city, and 70% of the sewers go to the same treatment plant for the entire county.


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## uaplumber (Jun 16, 2008)

Up here the code says Min. 1/4" per foot for 4" and under and 1/8" per foot over 4". It also states that " Steeper slopes and higher velocities will help keep the pipes clean by moving heavier solids that might tend to clog the pipes. I aim for 1/4" per foot as a guideline.


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## nhmaster3015 (Aug 5, 2008)

I don't believe any codes have a maximum allowable pitch for drainage piping, otherwise places like San Francisco would be in real trouble. Besides a vertical stack is about as "maximum" as you can get.


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## GrumpyPlumber (Jun 12, 2008)

uaplumber said:


> Up here the code says Min. 1/4" per foot for 4" and under and 1/8" per foot over 4". It also states that " Steeper slopes and higher velocities will help keep the pipes clean by moving heavier solids that might tend to clog the pipes. I aim for 1/4" per foot as a guideline.


*You sure you didn't mean 1/8" @ 4"?*


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## Alan (Jun 18, 2008)

GrumpyPlumber said:


> *You sure you didn't mean 1/8" @ 4"?*


It looks like those slopes were based on pipe size.


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## uaplumber (Jun 16, 2008)

GrumpyPlumber said:


> *You sure you didn't mean 1/8" @ 4"?*


 Oops, my bad! . Must have been too close to the primer again.


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## gear junkie (Jun 20, 2008)

IPC doesn't give a max slope. It only talks about minimum. If you look at the dfu chart, you'll see as the slope increases, so does it's capacity. From personal experience with sewer inspections, the section at a 45 where the lateral ties into the main is often the cleanest part on the entire line.


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## Kyle (Oct 4, 2008)

the larger you go. the less grade allowed. need to keep that good water flow on the bottem 2/3 of the pipe. if your goin 4 inch... pretty sure max is 1/2 per foot. but best is alway min grade


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## Ron (Jun 12, 2008)

Kyle said:


> the larger you go. the less grade allowed. need to keep that good water flow on the bottem 2/3 of the pipe. if your goin 4 inch... pretty sure max is 1/2 per foot. but best is alway min grade


I don't think there is a max slope, only the min.


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## Marlin (Aug 14, 2008)

I never heard of a max slope either. How would you make a vertical stack? How would you get sewage down a hill? I'm envisioning some poor misinformed individual looping pipe back and forth to get it down a hill without putting too much slope on it.


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## nhmaster3015 (Aug 5, 2008)

If there was such a thing as maximum slope then you would never be able to dump crap into a vertical stack.

As far as I know none of the code's address maximum slope, only minimum.


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## Redwood (Sep 8, 2008)

nhmaster3015 said:


> If there was such a thing as maximum slope then you would never be able to dump crap into a vertical stack.
> 
> As far as I know none of the code's address maximum slope, only minimum.


I guess that would make the maximum slope straight vertical! Huh?:laughing:


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## Protech (Sep 22, 2008)

I had in inspector tell me a few years back that The most I could put on a 4" line was 3/8". 45degree slope and steeper is considered a vertical drop. Between 3/8" and 45 is the "no-zone". Inspector was city of Orlando


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## Redwood (Sep 8, 2008)

Protech said:


> I had in inspector tell me a few years back that The most I could put on a 4" line was 3/8". 45degree slope and steeper is considered a vertical drop. Between 3/8" and 45 is the "no-zone". Inspector was city of Orlando


I guess he subscribed to the myth that liquids would "outrun" the solids...:laughing:


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## GrumpyPlumber (Jun 12, 2008)

*I see this topic as one of those endlessly debated topics that is largely based on personal opinion for lack of written code.*

*I go by what I was told by an old time inspector, I don't exceed more than an eight pitch over the required pitch, in other words, max 3/8" for 1/4" and 1/4" for 1/8".*

*Utah is the only one I know online or otherwise that can attest to excessive pitch causing potential problems, he once installed mock drains using clear piping, if I recall the excessive pitch caused debris to hang up on horizontal offsets.*

*I'll also say that it's the norm for exterior drains to be excessively pitched, but these drains are frequently in use over a 24 hour period.*

*They're also usually a straight shot to the sewer.*

*If debris were to get hung up on a drain that isn't so frequently used, I imagine it could dry in place and allow more debris to gather.*


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## Kyle (Oct 4, 2008)

i know that there is not actual " max" slope but Minumum grade is best no matter what. to much slope and you run into problems too. i am not talking a 45 or vertical but like 5% etc . when in doubt ask inspector


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