Main sewer line with more than 1/4 pitch...

[Niloc75]

Greetings. I had a plumber re-route the horizontal portion of main sewer line under the slab, but noticed that the pitch is more than 1/4"/foot. My guess is that it's closer to 1/2"/foot. Is this a problem? Everything I've read says 1/4 or less, but given that this horizontal portion does a 90 turn upward into a vertical stack, I'm a bit confused...

your advice is much appreciated!

 

[Sylvan]

Nothing wrong with a pitch of 1/2 per foot. The more pitch the more FU's you can connect on the same size pipe

 

[Sponsor]

 

[Jeff H Young]

not a problem or the code would have a max. 1/4 MINIMUM fall no one seems to understand minmum and maximum

 

[Niloc75]

Thanks guys. What's this stuff I've been told about "water outrunning the shit" if the pitch is too steep? Is that just B.S.?

 

[Niloc75]

And one more question: the attached pic is pretty close to how the basement bathroom drains will be installed under the slab. Do you have any (code violations or otherwise) concerns about this design? (Note: the tub will connect to drain from about 4 feet away). Much appreciated--

 

[Tuttles Revenge]

Water out pacing the solids isn't BS.. but its also not a problem in a home where the fixtures get used frequently as it will eventually all wash down.

I was trying to find the video that @Terry had posted on the site before which shows clear pipe set up and watching solids settle out after 30-40ft.

 

[Tuttles Revenge]

And one more question: the attached pic is pretty close to how the basement bathroom drains will be installed under the slab. Do you have any (code violations or otherwise) concerns about this design? (Note: the tub will connect to drain from about 4 feet away). Much appreciated--

View attachment 90658

If this style of venting is going to be used rather than horizontal wet venting, then the tub needs that vent replaced. But horizontal wet venting is the way to go.

 

[Niloc75]

Thanks Tuttle. This below diagram is a better example of how we were planning on having this installed. I was under the impression that the tub/shower combo (on the left) does not need a separate vent if it's located less than 5 feet away. But I've read a lot of your posts, and definitely trust your opinion... Can you confirm that below design wouldn't work, and if not, provide a few details on how the horizontal wet vent would work with below layout?

 

[Reach4]

You don't want too much slope on the trap arms (the pipe after the trap but before the vent).

 

[Niloc75]

You don't want too much slope on the trap arms (the pipe after the trap but before the vent).

Thanks, good to know. How much slope should I use for trap arms? Are you Ok with this design, from a venting standpoint?

 

[Reach4]

1/4 inch per foot for trap arms usually.

I am not sure. The people who know UPC can comment.

 

[Jeff H Young]

Thanks guys. What's this stuff I've been told about "water outrunning the shit" if the pitch is too steep? Is that just B.S.?

I wouldnt call it BS but i also think that is an extreme case where too much fall causes problems . I think people make more out of it .
on a trap arm excess fall can cause issue on long trap arms with lots of fall siphonage of trap can occur. it also tends to make the tail piece come up verticle out of plumb but I shoot for a 1/4 inch example a 3 ft arm isnt going to bother me with an inch of fall

 

[Niloc75]

Here's the latest design. Note: black for drains, gray for vents. Any potential problems here? thanks again--

 

[Reach4]

Looks good.

Vessel sinks with no overflow may not drain as well as lavatories with overflow. Put enough water in them, and they will drain fine,

 

[Jeff H Young]

The first drawing or second both work fine . note 42 inch max code length on the 1 1/2" trap arm for lav from the vent to the ptrap.

 

[wwhitney]

If this has been spelled out previously in this thread, I managed to miss it:

The problem with the rendering in post #5, and possibly post #8, is that with horizontal wet venting, the wye where the tub joins the lav is the vent connection for the tub, and that wye needs to be with 42" of pipe run and 1-1/2" of fall for a 1-1/2" tub trap arm. Certainly in #5 it looks like there's an extra jog downward just before the wye, which would exceed 1-1/2" of fall. In #8 it's unclear.

Also, if the 42" is the only sticking point, the tub trap can be up sized to 2" with a 2" trap arm, and then the limits become 60" of pipe length and 2" of fall.

That 42" also applies to the lav trap arm to the san-tee, and #8 looks like that could be exceeded. Upsizing a lav trap to 2" isn't really a good option.

And of course at the lav san-tee, the drain and vent both need to be 2" for wet venting the WC.

Cheers, Wayne

 

[Tuttles Revenge]

The rendering in #13 is the way I would install a horizontal wet vented system in Seattle. In that case the tub trap arm doesn't require its own individual vent because the dry vent of the sink takes care of it and venting the toilet. If the toilet is more than 5ft to the 4" main drain then the drain to the wall for the sink needs to be upsized to 3" for that branch End of the Line Cleanout. If its under 5ft then just a 2" cleanout at the wall.

 

[Niloc75]

The first drawing or second both work fine . note 42 inch max code length on the 1 1/2" trap arm for lav from the vent to the ptrap.

The rendering in #13 is the way I would install a horizontal wet vented system in Seattle. In that case the tub trap arm doesn't require its own individual vent because the dry vent of the sink takes care of it and venting the toilet. If the toilet is more than 5ft to the 4" main drain then the drain to the wall for the sink needs to be upsized to 3" for that branch End of the Line Cleanout. If its under 5ft then just a 2" cleanout at the wall.

Thanks everybody, super helpful. I've checked the trap arm lengths and distance to main, they are compliant.
............................................
some follow-up questions:

--So just so I'm clear, the dedicated tub/shower vent is not necessary, because the upstream lav/toilet vent will do the job?
--for the lav cleanout, how/where would you install this so that it's not hidden behind a finished wall?
--is it ok to use the all-in-one poly 1.5" waste/overflow drain for the tub, by using reducing coupler? I won't have much room to get the tub drain lined up, as it's against an exterior wall, and the 1.5 poly drain will probably be easier to install.
--any tips on how to get the tub drain installed in EXACTLY the right spot, given that it will installed before framing/insulation/wall tiles/etc?

 

[Tuttles Revenge]

--So just so I'm clear, the dedicated tub/shower vent is not necessary, because the upstream lav/toilet vent will do the job?

Yes

--for the lav cleanout, how/where would you install this so that it's not hidden behind a finished wall?

A 2" Cleanout tee is best above the san tee for the lav. It can be installed behind or even flush with the sheetrock and accessible with a chrome cleanout cover or a plastic access panel.

-is it ok to use a the all-in-one poly 1.5" waste/overflow drain for the tub, by using reducing coupler? I won't have much room to get the tub drain lined up, as it's against an exterior wall, and the 1.5 poly drain will probably be easier to install.

No. Since you won't have access to those parts, they need to be glued.

-any tips on how to get the tub drain installed in EXACTLY the right spot, given that it will installed before framing/insulation/wall tiles/etc?

We call this a Blind Set. It sucks. First things first. Set the tub in the alcove and get it perfectly level across the back and sides and scribe a line on your studs. Determine whether you need to place the tub in a bed/pads of mortar or just use a ledger board. How we do set up the blind set, is to build the waste and overflow of the tub first. The tub shoe meets the overflow at a san tee at the wall usually. So your trap needs to be set to receive that waste tee. You can measure the center of the tub drain from the corner of the actual tub, not the given dimensions. Get the trap in place but don't glue it together. Then guess the difference in height from the trap to the tub tee. Dry fit that into the trap and set your glued together waste and overflow on top with the tub out, then install your tub to your scribe line or on the ledger. See if the waste and overflow match up to your tub, use the rubber gasket on the shoe too, they need to be part of the measurement... If it does, you just won the lottery. If not, adjust what you need until they do. Once you have it all lined up and perfect mark your fittings to the pipe with a marker and glue it up. But act fast. Set the tub and install your screwed in drain and overflow pieces to double check.. if that checks out, let that assembly cure for a bit. Now you can pull the tub and place mortar if needed and re set the tub with little effort.

 

[CBme]

To your original question,708.1 specifies it means 1/4" minimum (though there is apparently some possible areas that allow for 1/8"). It doesn't list a maximum.

708.1 General​

Horizontal drainage piping shall be run in practical alignment and a uniform slope of not less than 1/4 inch per foot (20.8 mm/m) or 2 percent toward the point of disposal provided that, where it is impractical due to the depth of the street sewer, to the structural features, or to the arrangement of a building or structure to obtain a slope of 1/4 inch per foot (20.8 mm/m) or 2 percent, such pipe or piping 4 inches (100 mm) or larger in diameter shall be permitted to have a slope of not less than 1/8 inch per foot (10.4 mm/m) or 1 percent, where first approved by the Authority Having Jurisdiction.