Wet vent

[CaliforniaPlumber]

Hi,

I want to add a bathroom & laundry room and just wanted to double check I am venting correctly.
Is it ok to use the 2" lavatory vent for the shower & toilet as well?

 

[wwhitney]

No, there's a few issues with your diagram.

First, as background, every fixture needs a vent within one trap diameter of fall from the fixture trap outlet. There's also a length limit between the trap and the vent, which is 42" for a 1-1/2" trap and 60" for a 2" trap. A WC doesn't have the fall limit, but the length limit, including vertical drain portions, is 72" from the closet flange to the vent.

Now, the way wet venting works is that instead of having a vertical dry vent takeoff as your vent, the junction with another dry vented drain is the vent for your fixture. So if we delete the washing machine and the WC from your diagram, the lavatory drain could be the wet vent for the shower, as long as the shower trap arm, from the 2" trap outlet to the wye where the lavatory drain joins, is under 2" of fall and 60" of length.

Similarly, if we delete the shower and the washing machine, the same idea could work for the lavatory to wet vent the WC (and in this case the lavatory needs a 2" dry vent as you show, since WCs always require a 2" vent). Except I would guess from your drawing that the distance from the closet flange, down to the closet bend and the horizontally to where the lavatory drain joins is over 6'. If I'm mistaken, then that would work for just the dry vented lav and the wet vented WC.

However, this type of wet venting for a bathroom has a couple additional rules your diagram doesn't comply with. First, you have to vent each trap arm before it joins another trap arm. Ignoring the washing machine, starting at the WC you have the shower join first, and then the lav join. You can't join the two unvented trap arms; you'd need the lav drain to join the shower first, and then they both join the WC; or the lav join the WC first, and the shower joins.

Except for another rule, which is that the WC has to be last wet vented fixture, so that second order isn't an option. Starting at the lav, it first must join the shower, then join the WC, if you want the lav to wet vent both the shower and the WC.

And lastly, the wet vent has to carry only bathroom fixtures. So you can't bring the dry vented laundry drain into the middle of the bathroom group. The laundry drain needs to join the branch drain downstream of all the wet vented fixtures, including the lavatory drain providing the vent.

One way to fix all the above problems would be to add a 2" dry vent to the shower trap arm before it joins the WC. Then the shower would be wet venting the WC, and that's it for wet venting. [Also the lav vent could be only 1-1/2" in this case, as it's not involved in the WC venting.] But I'm guessing that's not a viable option given the shape of the shower you've drawn, you won't have any solid walls around the shower near where the drain is currently shown.

Cheers, Wayne

 

[Sponsor]

 

[CaliforniaPlumber]

Thank you for these details. I corrected the original drawing and added the 2" vent shared by shower and WC. Does this look ok?

 

[wwhitney]

No, there's two problems:

First, a dry vent has to come off vertically (top half of the horizontal trap arm) and rise vertically (at most 45 degrees off plumb) to an elevation of at least 6" above the fixture flood rim. So your vent can't be horizontal below the floor. Unless you have a wall between the shower and the WC, or your drains are quite deep below the WC, the vent would be rising into the room and be exposed, which I assume you don't want.

Second, a WC has to be last on a wet vent. That means you can't use a dry vented WC to wet vent the shower. That's why I indicated that the dry vent would have to be on the shower trap arm; then the dry vented shower could wet vent the WC.

You could do something circuitous, like send the shower trap arm to right, with a LT90 to run under (or alongside and almost under) the wall on the right, then take off a 2" dry vent with an upright combo (rolled slightly so the vent emerges in the wall if the trap arm is running alongside but not directly under the wall), then hit a LT90 to go back to the left, and then hit the 3" WC drain with a horizontal 3x3x2 wye to wet vent the WC.

Or you could something similar with the lav drain, have it enter the floor to the right of the WC drain, travel down and to the right to intersect the shower drain and wet vent it, and then the combined shower/lav drain would intersect the WC drain and wet vent it.

Cheers, Wayne

 

[GReynolds929]

The laundry drain needs to connect downstream of the lav and wet vent in my area.

 

[CaliforniaPlumber]

Thank you Wayne. After doing more research and putting your last paragraph in picture, I believe I was able to use a single wet vent for the bathroom group. Please correct me if I'm misunderstood your comment.

It would be nice to add a floor drain in the utility room, but I can't think of a way to do so without its own vent. Unless you have an idea?

 

[Reach4]

I think everybody will like that one.

I don't know the rules on adding that "emergency floor drain" to your system under UPC.

 

[wwhitney]

It would be nice to add a floor drain in the utility room, but I can't think of a way to do so without its own vent. Unless you have an idea?

Your floor drain would require a trap seal primer as per UPC 1007.

Chapter 10 Traps and Interceptors: Traps and Interceptors, California Plumbing Code 2022 | UpCodes

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As far as venting it goes, since it's near the same wall as the lav drain, it shouldn't be hard to dry vent it through that wall, and the dry vent could combine with the lav vent at an elevation at least 6" above the lav flood rim.

You can also horizontally wet vent it just like the shower, if the trap arm from the floor drain to the connection to the lav drain is at most 5' assuming a 2" trap. It would need to connect to the lav upstream of the WC, and it could either connect downstream of the shower or upstream of it.

Again, each fixture has to connect to the lav drain /wet vent one by one, you can't join the floor drain trap arm to the shower trap arm before either of them joins the lav drain / wet vent.

Cheers, Wayne

P.S. Just to confirm, your diagram shows 5' horizontally from the closet flange to where the WC drain joins the lav drain / wet vent. The applicable length limit also counts any vertical drain sections, such as from the closet flange to the closet elbow. And then the total length limit is 6'.