rough-in under slab:

Plumbing Forums

Help Support Plumbing Forums:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

colinga75

Member
Joined
Jan 15, 2023
Messages
8
Reaction score
0
Location
98115
Greetings. I'm in the process of roughing in a bathroom under the slab, and want to make sure it's up to code (I'm in Seattle, for what it's worth). The attached diagram is how I was thinking about doing this. Note, the bathtub/shower combo (on left) drain would connect from about 4 feet away. Does the tub/shower need a separate vent? Comments/concerns/suggestions are welcome--Bathroom Plumbing Diagram2.jpg
 
You need to include pipe sizes, fitting callouts, some dimensions, and what is coming down the dark line at the far right of your sketch. I assume you are using the black lines as drains and the gray lines as vents?

If I assume the dark vertical line on far right is the main stack from the rest of the house, (making this a basement rough in?), then there is no reason to connect the vent line into the horizontal sewer line under the slab right next to the stack. The vent just needs to connect to the main stack above the flood plain of the last fixture that drains into the stack like in the attic.

The combined toilet and tub/shower line needs to enter the main horizontal sewer at a 45-degree angle to channel the flow in the direction of the main line. You show that where the tub/shower connects to the toilet line. Depending on the distance the sink is from the vertical vent/drain line from the tub, it will likely need to be vented before it reaches that line. That will all be above the slab at least.

Fitting selection and orientation of those fittings is critical for the various parts of this system, both under and above the slab.

Provide the needed information and better comments can be provided on your installation.
 
Thanks for the reply. The diagraming software I'm using kind of sucks, but I made an updated picture (below). Note: black for drains, gray for vents, and I will definitely use all the correct wyes/fittings/etc (just hard to draw all that stuff into this diagram).

Let me know what you think, much appreciated--
 

Attachments

  • Bathroom Plumbing Diagram6.jpg
    Bathroom Plumbing Diagram6.jpg
    521.7 KB
Last edited:
Understand about the software. :confused:

The new sketch looks good assuming the required dimensions are maintained, and the orientation of the fittings are correctly installed. The main lookout would be the connection of the sink drain line to the toilet drain line. In your latest sketch, the toilet will be wet vented through that drain line and then through the dry vent for that sink. But a vent line needs to be vertical or no more than 45 degrees off vertical until it reaches 6" above the flood plain of the vented fixture. So, the sink drain line wye needs to enter the toilet drain line vertically or rolled at a 45-degree angle and continue that angle or go vertical until it reaches 6" above the top of the sink to properly vent the toilet. Depending on the depth of your sewer line and the distance from the wall, that may be difficult to accomplish.

And best practice would be that the tub drain line wye into the toilet drain line would also enter that line at a 45-degree angle from above.

For the sink, if you have the elevation, I would use a reducing wye vertically directly under the toilet with the branch line angling up and entering the wall directly behind the toilet. That branch line could then go vertically up the wall and the sink could drain into it eliminating the sink drain going into the horizontal toilet drain line under the slab on your sketch. That branch line would then act as a wet vent for the toilet and the drain line for the sink. It obviously will need to continue up the wall and be connected to the horizontal vent line from the tub P-trap.
 
Understand about the software. :confused:

The new sketch looks good assuming the required dimensions are maintained, and the orientation of the fittings are correctly installed. The main lookout would be the connection of the sink drain line to the toilet drain line. In your latest sketch, the toilet will be wet vented through that drain line and then through the dry vent for that sink. But a vent line needs to be vertical or no more than 45 degrees off vertical until it reaches 6" above the flood plain of the vented fixture. So, the sink drain line wye needs to enter the toilet drain line vertically or rolled at a 45-degree angle and continue that angle or go vertical until it reaches 6" above the top of the sink to properly vent the toilet. Depending on the depth of your sewer line and the distance from the wall, that may be difficult to accomplish.

And best practice would be that the tub drain line wye into the toilet drain line would also enter that line at a 45-degree angle from above.

For the sink, if you have the elevation, I would use a reducing wye vertically directly under the toilet with the branch line angling up and entering the wall directly behind the toilet. That branch line could then go vertically up the wall and the sink could drain into it eliminating the sink drain going into the horizontal toilet drain line under the slab on your sketch. That branch line would then act as a wet vent for the toilet and the drain line for the sink. It obviously will need to continue up the wall and be connected to the horizontal vent line from the tub P-trap.
Outstanding, thanks. Couple more questions for you:
--I've just got some additional info from a retired plumber who said the tub/shower vent is not necessary, as its venting would be handled by the toilet/lav vent. Your thoughts?
--someone else suggested a cleanout for the lav... I assume that would have to be installed behind the finished wall, making it difficult to get access to. Is that correct, or is there a more accessible location for that?
--is it ok to use the all-in-one poly 1.5" waste/overflow drain for the tub, by using a 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?

much appreciated--
 
Last edited:
Outstanding, thanks. Couple more questions for you:
--I've just got some additional info from a retired plumber who said the tub/shower vent is not necessary, as its venting would be handled by the toilet/lav vent. Your thoughts?
--someone else suggested a cleanout for the lav... I assume that would have to be installed behind the finished wall, making it difficult to get access to. Is that correct, or is there a more accessible location for that?
--is it ok to use the all-in-one poly 1.5" waste/overflow drain for the tub, by using a 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?

much appreciated--
Venting the tub by the toilet/lav vent? Not the way you have shown in your sketch or in my suggested drain system. You would have to do something like the lower bath in the following diagram, and that would also require the distance from the P-trap to the vent isn't too long. It would not be per code as your vent would be horizontal before it reached 6" above the flood plain of the tub, and that horizontal piece would be a wet vent as well.

1675923224113.png

Providing a clean out for the lavatory? With your short runs, as long as you don't use a totally glued P-trap, you probably don't need that. But if you do provide one, it would in the wall, and you use a cover like this.
1675923775420.png

Using an all-in-one poly 1.5" waste/overflow drain for the tub, by using a reducing coupler? Normal tubs have 1 1/2" drains, so I'm not understanding your question about using a reducing coupler for the waste/overflow assembly.

How to install the tub drain in exactly the right spot? Run the horizontal tub drain line to the measured location of the P-trap weir leaving a little wiggle room. Box out the concrete so that the P-trap and the tub drain/overflow assembly can be installed in their exact required locations.
 
Good stuff, thanks again. I'll stick with the original plan and keep the dedicated tub vent. Re: the 1.5 poly assembly, the reducing coupler would reduce from 2" tub trap down to 1.5. Is that OK, from a code perspective? And, is it OK to have more than 1/4 inch pitch on all of this stuff, so I don't have to bury everything so deep in the ground under the concrete? And regarding burying... I'm working with hard clay-like dirt---do I need to use anything else, like sand, gravel, etc?
 
A tub only needs a 1 1/2" P-trap even if there is a shower in it. If it was just a shower base, then you would need a 2" P-trap. But to answer your question in case you have a tub with a 2" outlet, yes it would be acceptable to reduce the drain line from a tub to 1 1/2". But it would not be acceptable to reduce a shower base from its required 2" P-trap to 1 1/2" after the P-trap.

You MUST maintain only a 1/4" per foot slope from a shower or sink drain to where the vent is located. After the vent connection, your slope can be increased. However, any line that can have solids in it, i.e. the line from the toilet and the main sewer line, must not have a slope more than 1/4" per foot for 3" or 1/8" per foot for 4" and above. Excess slope in those lines can result in solids accumulating and not being flushed downstream creating a blockage.

You should use sand as a bed for the buried pipelines which will allow easier control for getting your slopes right as well as protecting them from thermal expansion and contraction. They should also be covered in sand as well to protect them from the gravel base used under the concrete.
 
Thanks man. My 4" sewer main coming from stack is probably 1/2 inch pitch (I had a plumber/friend put that in, and he apparently put too much pitch on that). It's been working great for months and gets a lot of use/water flow, but maybe that's not enough time for problems to build up. At this point, would you go so far as lengthening the sewer stack to achieve proper slope? I've been advised to not worry about this, given the usage/etc.

The 1/8 pitch for the 4" still kind of confuses me, given that it's carrying waste straight down before going horizontal.
 
The 1/8 pitch for the 4" still kind of confuses me, given that it's carrying waste straight down before going horizontal.
The 1/8" per foot is obviously only for the horizontal portion of the line. The vertical line is fine as the solid wastes fall down the pipe and get flushed into the horizontal line where they need to be carried by the water flow along the line.

1675959144446.png

A 1/2" per foot slope is the absolute maximum as indicated from the drawing above. I wouldn't change it now that it is installed.
 
The 1/8" per foot is obviously only for the horizontal portion of the line. The vertical line is fine as the solid wastes fall down the pipe and get flushed into the horizontal line where they need to be carried by the water flow along the line.

View attachment 39021

A 1/2" per foot slope is the absolute maximum as indicated from the drawing above. I wouldn't change it now that it is installed.
The 1/8" per foot is obviously only for the horizontal portion of the line. The vertical line is fine as the solid wastes fall down the pipe and get flushed into the horizontal line where they need to be carried by the water flow along the line.

View attachment 39021

A 1/2" per foot slope is the absolute maximum as indicated from the drawing above. I wouldn't change it now that it is installed.
phew! thanks again...
 
Greetings. I'm in the process of roughing in a bathroom under the slab, and want to make sure it's up to code (I'm in Seattle, for what it's worth). The attached diagram is how I was thinking about doing this. Note, the bathtub/shower combo (on left) drain would connect from about 4 feet away. Does the tub/shower need a separate vent? Comments/concerns/suggestions are welcome--View attachment 38998
Best bet would be to wet vent from the lavatory sink... I'm in the Seattle area
 
Back
Top