DWV Questions

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EJ3

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My county uses the 2018 IPC. I am in the process of installing underslab DWV and a have a few questions:

My trunk line is fairly deep to accommodate the kitchen sink which is 50+ feet on the other side of the house. I am planning to run all of my fixture drain lines and vents at a more shallow depth turning down into the trunk lines using wyes with street 45s, turned vertically or rolled.

1. For the Master toilet vent line I am planning to use a 3” x 2” wye with street 45 turned vertically, then 90 over (medium bend) to the exterior wall, 90 up (LS 90) in the top 1.5 courses of CMU, then the 2” VTR. The top of the pipe will only be a few inches below the slab. See attached fitting layout. For the sink I plan to use a sanitary tee in the VTR to catch the sink trap arm. Since it will be 4’-9” between the two, I will re-vent a 1.5” line above the ceiling, or maybe consider using a 2” trap arm line.

Is this acceptable?

2. For the Master shower I will be using a HC accessible shower with a low threshold, so for extra precaution I am also putting a FD just outside the shower. The shower & FD will drain down vertically into the trunk line as described above. The shower vent will run to the back wall then tie to the 2” VTR above the ceiling. See attached fitting layout.

Is this acceptable?

3. And regarding the P-traps, which orientation is correct (see attached)? Does it even matter?

Thanks in advance.
 

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John Gayewski

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1. You can't tie the kitchen sink into your wet vented toilet. You could run a separate vertical dry vent for the toilet. Or tie the kitchen sink into the drain farther down after the toilet is vented by the lav

Not sure it matters which way you orient the trap but the more vertical side gets the short 90 I think.


You can't drain into a santee on its back. Not to mention the horizontal dry vents below the flood rim. A dry vent needs to be vertical from the start until your 6" above the fixture it serves.

If that's not possible due to structural conditions you'll need an accessible cleanout in the vent risers because they will clog over time. Generally it's possible to get a drain and vent system that doesn't require maintenance and that's preferable.

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Reach4

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3. And regarding the P-traps, which orientation is correct (see attached)? Does it even matter?
Steep drop on the input side is a little better.
 
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wwhitney

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0) Running the whole bathroom group together at a shallower depth than the kitchen sink drain, and then just combining the whole bathroom group branch with the lower kitchen sink drain all at once, is the way to go. That gives you options on venting the bathroom fixtures.

1) If you want to dry vent the WC, then your vent can not go horizontal below the slab. So you'd need to figure out a WC drain routing that would get the drain close enough to the vent wall so that a dry vent can rise at a 45 degree angle from plumb and make it under the wall before emerging above the slab.

Or you could wet vent the WC by bringing your dry vented lav fixture drain to join the WC fixture drain. Note "fixture drain" means one fixture only, vs branch drain means multiple fixtures.

2) Same issues and solutions as (1). The lav/WC branch could wet vent the shower and the floor drain. In which case the shower and floor drain trap arms run from the trap outlet to the wye where they join the branch (separately as fixture drains, don't combine them before they individually join the branch). And those trap arms are limited to one pipe diameter of fall, so the depth at which you set the horizontal bathroom branch will determine the depth at which the traps should be.

Cheers, Wayne
 
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EJ3

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Thank you for the replies.

I would only use the sanitary tees for tying the trap arm into the vent or re-venting. The sink is actually from the bath. The kitchen sink ties into the trunk line and will have a 1.5” VTR back at the trap arm tie-in point. Hopefully the attached clarifies what I want to do at the toilet. The blue pipe are the low lines and the red pipe are the more shallow lines.

My layout and CMU stem wall construction makes it difficult to not vent the toilet without some horizontal pipe below the slab. But since this will be a wet vent, will that be okay? I think regardless I will put a wall cleanout in the 2” vent pipe.

Regarding the shower and floor drain, I think I can run to the other trunk line where I have a wall to run the vent vertically, between the drains and the turndown.

Regarding a bathroom or laundry room emergency floor drain, does the IPC even require venting?

All feedback is greatly appreciated.
 

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wwhitney

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I don't see any problems with the layout shown in your drawings. If the lav trap to stack distance is less than 6' and you can run the lav trap at 1/4" per foot to have less than 1-1/2" fall, and you use a 1-1/2" lav trap, you may eliminate the revent on the lav fixture drain.

If you'd like to use the lav to wet vent everything in the bathroom, the drawing below is what I suggested, using your red = shallow, blue = deep convention. The topmost (on the page) point of the red lines is where the shallow bathroom branch dives down to connect with the deep building drain.

This assume that the 2" shower trap arm will be under 8' in length and 2" in fall. The little offset at the shower drain just represents the u-bend of the trap and is so that the shower trap arm doesn't run into the floor drain. This also assumes that the trap on the floor drain can be set low enough that the floor drain trap arm is horizontal; I've not worked with floor drains before.

Cheers, Wayne

master bath - plan.jpg
 
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EJ3

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Wayne,

Thank you for the confirmation and suggestion.

I have another bath that will use a wet vent for the toilet. But since it is farther away and more shallow, I will probably roll the 45 like in the attached diagram.

Thanks, Ed
 

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wwhitney

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To be clear, that diagram is not allowed for a dry vent, as the dry vent can't be horizontal unless 6" above the WC flood rim.

For a wet vent, the wye would typically be flat (horizontal, 2% slope on both inlets), and of course the wet vent 90 would need to be a LT90 as it is carrying drainage. I don't believe there's any prohibition on rolling the wye up 45 degrees as shown.

Cheers, Wayne
 
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EJ3

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For the 2" drain line coming from the kitchen, it will be a continuous 1/4" per foot slope for about 50 ft with no other drain lines tying into it. Will it need a vent between the 1.5" vent at the kitchen sink trap arm tie-in point and where is ties into the 3" line?
 

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John Gayewski

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For the 2" drain line coming from the kitchen, it will be a continuous 1/4" per foot slope for about 50 ft with no other drain lines tying into it. Will it need a vent between the 1.5" vent at the kitchen sink trap arm tie-in point and where is ties into the 3" line?
I think a cleanout would be a good idea. It shouldn't need a vent, but getting a snake 50' after two op degree turns might be tough. Kitchen drains are one that can tend to clog.
 
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