View Full Version : minimum waste pipe slope

04-07-2006, 06:38 AM
Need to place a hole in a concrete wall to be poured for a waste pipe serving a toilet in a commercial building. Trying to determine the elevation of the waste pipe when it will exit the building. The run to the sewer connection is long and the sewer connection elevation is shallow. We are trying to avoid the use of a lift station and would like to keep the depth of this run at a minimum. One plumber told us to plan on a 12" straight drop from the floor flange to the waste L then maintain a 1/2" per foot slope to the wall (14 foot run). This slope seems to be excessive. If 4" pipe is used I would think a slope of 1/8 to 1/4 per foot would be enough. Thankyou for any help. This wall needs to be poured and I'm having a heck of a time getting another plumber over to look at this design.

Bob NH
04-07-2006, 06:55 AM
The codes usually require a slope of 1/4" per foot.

The design from the floor down can be made the minimum of what it takes to put in the required fittings. If minimum depth is critical, then use the dimensions for the fittings to be used; probably the minimum size closet bend with adequate allowance for the flange.

You also need to allow for any other fittings in the run, such as for venting.

04-10-2006, 07:03 AM
Bob NH,
Thankyou for your reply. All fittings for venting and lav tie in will be in the run so we are planning on a minimum closet 90 and head for the sewer.
All the properties on this street are having problems tieing into the sewer because of the sewer entry elevations. The contractor who installed the line didn't adhere to the specs and the city didn't catch him before he left town. The bond he posted doesn't even come close to the funds needed to correct the situation so all the property owners are stuck holding the bag. Thankyou again.

04-10-2006, 07:12 AM
Use a 4" pipe and you can run it at 1/8" per foot. 3" would have to be at 1/4" per foot under most codes. No code requires 1/2" per foot. But even more important that that is how you layout the fixtures and piping arrangement. By being judicious, you might even be able to start the plumbing line 6" center below the finished floor.