Thread: Slope of a waste line

This is a waste line for a kitchen sink, the line is vented with a vent stack in the wall behind the sink. Is this slope excesssive, is it not to exceed 1/2 inch per foot? Or does that only apply to the trap arm

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This is what I found
2006 IRC

P3005.3 Horizontal drainage piping slope.

Horizontal drainage
piping shall be installed in uniform alignment at uniform
slopes not less than 1/4 unit vertical in 12 units horizontal
(2-percent slope) for 21/2-inch (64 mm) diameter and less, and
not less than 1/8 unit vertical in 12 units horizontal (1-percent

slope) for diameters of 3 inches (76 mm) or more.

What is the difference if it has a long slope or if when it comes out of the cabinet and goes straight into the crawl to ground level and then 45s into the waste line. The slope gets pretty drastic when the waste line gets to the street connection

Straight drop, long slope?

Someone from the plumbing dept will correct me if I'm wrong. If the vertical angle is less than 45 degrees but more than the usual 1/4 " per foot, some sludge will be left behind.
A pipe at 45 degrees or steeper will flush just as well as a vertical pipe.

So that mess is the work of an amateur that never read the plumber's handbook.

Having said all that, is there a big concern here, with crap clogging the line? Does shitt stop sliding at 44 degrees?

Originally Posted by John Kogel

Someone from the plumbing dept will correct me if I'm wrong. If the vertical angle is less than 45 degrees but more than the usual 1/4 " per foot, some sludge will be left behind.
A pipe at 45 degrees or steeper will flush just as well as a vertical pipe.

So that mess is the work of an amateur that never read the plumber's handbook.

Having said all that, is there a big concern here, with crap clogging the line? Does shitt stop sliding at 44 degrees?

I guess that may depend on what the particular person ate

1/4" per foot. The standard issue with excessive slope is that the water will outrun the solids and the solids will be left behind and eventually you'll have problems. The initial, upper run in the photo, could be a problem. The lower run is steep enough it will probably be Ok.
My bigger concern is the sewer connections and I would recommend putting a note of concern in the report. The abandoned connection at the left side of the photos looks more like the original connection. The current ground connection looks newer, DIY, not quite kosher. From the picks I would put something in the report, further eval by plumber, camera the line, etc. Or maybe you saw enough to put comments in the report.
Obviously the insulation and dirt concerns are already in the report.

Thank you. This pretty much says it all. I was just a little confused about slope after reading the code book. It's like that damn thing is written in latin.

The relief valve on the water heater is wrong in your new picture you posted unless it has a 12" sensing element on it.

Moving slightly to the edge of this topic.... The standard reason given for the code not allowing slopes between 1 in 24 and 1 in 1 is that the water will outrun the solids it is carrying, leaving the waste behind to clog the line up. I wonder how often this happens in practice. One neighbourhood I know has streets along the contours and the slopes of many of the building sewer pipes from the houses to the street are in the disallowed range. Visual camera inspection on two such pipes (30 and 70 years old) showed no significant solid build up. Clogs that do occur are caused by roots growing into the pipes, which are then either cleaned out (a few hundred dollars every one or two years) and/or replaced (typically $2000 to $8000 one time). This happens whether or not there any suspect trees in on the property. If the house is of an age such that its underground sewer pipe is likely to be clay sections, the probability of future clogs and sewer backups due to root problems is significant and should be mentioned. In comparison the probability of clogs due to excessive slope seems remote and therefore likely should not be mentioned. Maybe it's different with smaller pipes.

The 180 degree change of direction requires a clean-out. That particular no-hub fitting is not listed for plastic pipe. None of the waste pipe is supported. The water heater vent connector is not screwed to the draft hood. The water heater is located in the required clear working space in front of the electrical panel board. And what's up with the hose clamp on the copper pipe? It appears that the threaded copper fitting leaks.

David, Cleanout, are you crazy? Do you know how much that would eat into the plumbers profit margins . This is one of the most overlooked requirements I swear. Instead of buying a 90, the poor guy has to buy a tee, female adapter and threaded plug. While were at it lets make sure any possible cleanout is located where the drywaller will definitely cover it up.
It's unfortunate that something as simple as putting in a couple cleanouts has to be such a big deal to get a guy to do.

The reason behind the 1/4 per foot slope is they are trying to maintain the drain runs at 33% full capacity to wash out solids. Well this what we were taught in trade school in Canada. Also regarding the cleanouts by code in Canada you also have to have a cleanout every 50ft and every change of direction on the main sewer. I know I do this when roughing in homes or upgrading the plumbing but not very many plumbers do this, as stated above it cuts in to there profits or that extra few bucks may cause them to loose the job. But when I have to start cutting corners to get a job I walk away from it not worth the headaches later.

UPC requires minimal of 2%, 1/4" per foot grade on horizontal waste piping, piping greater than 45 degrees of horizontal is considered both horizontal & vertical. There are no maximum slope restrictions, but true solids will be left behind, build up will be washed out with the excessive slope. Clean out aren't required on waste lines ran greater than 72 degrees of horizontal. Plastic piping needs to be supported at no greater than 4 foot intervals. I see numerous defences and sure there are more out of viewing range. Also for dirty arms, the weir of the trap can never be above the vent take off. This restricts excessive slope from being allowed on trap arms.