Another vent question

[Chad schreiber]

Hi, I’m having our downstairs basement rough plumbing done and want to get some input on the purposed layout. Hopefully my drawing makes sense.
We have a half bath on the first floor, the drain stack comes down through the floor/wall, turns and goes out to the septic. We are installing a full bath downstairs and all the waste/drain pipes will be under concrete when finished.
I have basically three questions:

1) is it ok for the shower trap to be about 18” from the actual shower drain?
2) should there be a vent between the shower trap and W/C? I’m told everything will vent fine the way it’s purposed.
3) are there any other issues or concerns with the layout? A better way to do it?

All bends will be sweeps(just hard to draw them). I thought there should be a vent between the shower trap and the W/C but again, I’m told it’s fine. I’ve also never saw the actual trap for the shower anywhere but directly under the drain itself.

Thanks much for any thought!

 

[wwhitney]

1) You are allowed up to 30" horizontal offset (per IPC 1002.1), but it's generally not a good idea for the shower, and there's nothing in your diagram that suggests any reason to locate the trap anywhere other than directly underneath the shower drain.

2) In your diagram (which is really too small to be read, a higher resolution is required, and the correct orientation would be preferred), none of the shower, WC and lav are vented. The stack carrying drainage from upstairs may not serve as the vent for fixtures on this level (*). A dry vent for one of these fixtures would either have a path to a roof vent through vent pipes carrying no drainage, or could terminate in an AAV.

Now if you provide a dry vent on the shower trap arm (within 2" of fall from the trap outlet, assuming a 2" trap), that will dry vent the shower, and the shower drain may then wet vent the WC. The lav trap arm would require its own dry vent.

3) If you want to wet vent both the shower and the WC using a dry vented lav, and there's sufficient space in the wall to cross the stack, you could run the vented lav drain in the wall to the left so that it joins the shower trap arm. That would let the dry vented lav wet vent both the shower and the WC.

Cheers, Wayne

(*) There is IPC 913 on "Waste Stack Vent," but that does not apply, as such a waste stack vent may not carry the discharge of WCs. There is also IPC 917 on "Single-Stack Vent System," but I'm not particularly familiar with its provisions.

 

[Sponsor]

 

[wwhitney]

There is also IPC 917 on "Single-Stack Vent System," but I'm not particularly familiar with its provisions.

OK, my first perusal of IPC 917 suggests that, surprisingly to me, your diagram would comply if the following conditions are met. Take this with a grain of salt as I'm not so familiar:

- The stack is limited to 2 branch intervals in length, which would means at most 2 stories above this bottom level.

- If the stack is 3" (rather than 4"), it may receive at most 2 WCs (so just one from the floor(s) above) and at most 24 DFUs total (not likely to be a limit).

- The stack needs to rise vertically through the roof full diameter. If there are any horizontal offsets in the portion of the stack carrying drainage, a separate vent is required for the portion below the offset.

- If the WC is less than 18" of horizontal developed pipe length from the stack, then the shower trap and drain are limited to 1-1/2" (seems odd to me)

- The WC must be at most 4' from the stack in developed length, or 8' if the branch connects to the stack with a san-tee.

- The shower and lavatory must be at most 8' from the stack in developed length, or 12' if the branch connects to the stack with a san-tee.

- If the lav or shower fixture drains (which start at the trap outlet) have any vertical sections, they must be at least 2" in diameter and drop at most 4'.

Cheers, Wayne

 

[Chad schreiber]

Thanks, that’s a lot of info. If I understand what you stated my WC is fine, it’s 18” or less from the stack. The shower drain has no vertical runs and I can easily get the required drop. I think 2” was planned for the shower drain so yes, 1 1/2 seems odd to me as well.i will assume the purposed install without a vent for the shower will be fine and not create any draining issues?
One other question, is it correct to come off the shower drain with a sweep then go approx 18” to a trap then on through the drain? Like I said earlier, I’ve never saw a setup like that but with my limited knowledge it doesn’t seem Like it will cause any issues…. I think they are putting it in that way so there is less floor to cut out under the shower. Where all the other drains will be installed was not poured and is an open cavity area.