# Sanitary Slope for Low Flow Toilets



## Mech (May 7, 2020)

Is there a consensus or rule of thumb for minimum sanitary pipe slope for commercial buildings with low flow plumbing fixtures?  The urinal is 0.125 gpf, lavs are 0.35 gpm max, and toilets will be either 1.0 or 1.28 gpf.

I read a paper from Sloan Company, but there was no information other than more water and steeper is better.  It did not give a minimum slope to use.

The 2015 IPC allows an 8" pipe to slope at 1/16" per ft.  If I read the California Plumbing Code correctly, the minimum slope for any pipe size appeared to be 1/8" per ft and I am thinking that perhaps I should not slope less than 1/8" per foot.

Does anyone have any solid information?

Thanks


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## classicT (May 8, 2020)

Using the 2015 UPC to answer.

Why would you ever have an 8-in drain? An 8-in can handle 3600/2640 DFU (vert./horiz.).Never needed more than a 4-in in 99% of buildings I have been around. A 4-in can handle 256/216 DFU.

UPC 708.1 requires that all drainage piping be sloped 1/4-in per foot unless, where approved by the AHJ, 1/8-in per foot is required due to depth of sewer tie-in, structural features, etc.


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## Paul Sweet (May 8, 2020)

IPC Table 704.1 requires 1/4" per foot for pipes up to 2 1/2", and 1/8" per foot for 3" - 6" pipes.  I've always specified 1/4" per foot for low flow fixtures.


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## classicT (May 8, 2020)

Paul Sweet said:


> IPC Table 704.1 requires 1/4" per foot for pipes up to 2 1/2", and 1/8" per foot for 3" - 6" pipes.  I've always specified 1/4" per foot for low flow fixtures.


I'd agree that this is the best practice. 1/8 per ft. on low flow seems like a problem waiting to happen.


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## Mech (May 8, 2020)

Thank you for the responses.



Ty J. said:


> Why would you ever have an 8-in drain? An 8-in can handle 3600/2640 DFU (vert./horiz.).Never needed more than a 4-in in 99% of buildings I have been around. A 4-in can handle 256/216 DFU.



This is a 600,000 sf spec building.  "If you build it, he will come" or in this case, they will come.  Our client likes to install oversized pipes to handle any future load.  It costs them money up front, but they should avoid tearing up the majority of the floor in the future.  They just tear up enough to get to the pre-installed sanitary lines.


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## ADAguy (May 9, 2020)

Mech said:


> Thank you for the responses.
> 
> 
> 
> This is a 600,000 sf spec building.  "If you build it, he will come" or in this case, they will come.  Our client likes to install oversized pipes to handle any future load.  It costs them money up front, but they should avoid tearing up the majority of the floor in the future.  They just tear up enough to get to the pre-installed sanitary lines.



Love, exceeding minimums


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## e hilton (May 10, 2020)

If its a spec building, don’t pour the slab over the pipes.


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