Dry Vent for Shower - Fitting Question

[Paul E.]

I am working on a remodel of a shower that was originally wet vented. Currently the shower ties into the main 4" sewer line downstream of a toilet, so I would like to add a dedicated dry vent to help prevent any siphoning of the shower p trap from occurring.

In the sketch below, is it acceptable to use two 60 degree ells as drawn? The vent line needs to move horizontally in order to land inside a wall. When I mocked this up with two 45 fittings, I gained too much vertical height and not enough horizontal length to land in the wall.

 

[wwhitney]

I am working on a remodel of a shower that was originally wet vented. Currently the shower ties into the main 4" sewer line downstream of a toilet, so I would like to add a dedicated dry vent to help prevent any siphoning of the shower p trap from occurring.

Have you had any problems with siphoning? Wet venting works when implemented properly, so you may just be making more work for yourself. Having the shower wet vented downstream of the WC would require that you are under the IPC, not the UPC, and that the branch drain the shower connects to is carrying only bathroom fixtures from at most 2 bathrooms. [Although I guess there is a little more flexibility with so-called circuit venting, which I am less familiar with.]

As to your venting question, that's a slightly tricky question.

Technically the answer is no, as the IPC and UPC both define "vertical" as at most 45 degrees off plumb, and require the dry vent to rise vertically until at least 6" above the fixture flood rim.

However, a common way to take a dry vent off a horizontal trap arm that stays horizontal is to use a wye that is rolled 45 degrees off being upright-most. That similarly produces a vent with an elevation angle of 30 degrees, meaning it requires a 60 degree elbow to turn vertical when the vent gets under a wall. That this practice technically violates the "vertical" requirement seems to be almost universally overlooked.

Whether your jurisdiction would take the same attitude towards the configuration shown I can not say. One difference from the previous case is that your vent starts off vertical and then reduces its elevation angle, while in the previous case the vent takeoff starts off at a reduced elevation angle.

Can you shift the san-tee over far enough that you can use 45s for your vent and stay within the wall, and then offset the drain location below the san-tee as required?

Cheers, Wayne

P.S. A sewer is a sanitary drain (sufficiently far) outside the footprint of a building. You presumably wanted the term "building drain", which is what exits the building to connect to the sewer.

 

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[Paul E.]

Hey Wayne,

I am subject to 2021 UPC. Does the UPC prohibit wet venting a shower downstream of a WC?

The main reason I would like to introduce a vent at this location is so I can raise the shower p trap up. It's my understanding that I cannot fall more than one pipe diameter along the shower trap arm before it joins up with the wet vent. I would like to raise it vertically up more than one pipe diameter, so I figured adding the vent to the trap arm was my only option.

Reading through the threads on here about a wye + 60 degree fitting is what caused me to wonder if I could do what I proposed. I will see about shifting the sanitary tee closer to the wall I want the vent to come up in, to make two 45s work.

In terms of vertical pipe runs, should I be thinking of a 60 degree fitting as 30 degree fitting? Since it is less than 45 it would not work, whereas 22.5 (67.5 off vertical>45) degree fittings are appropriate to use?

I appreciate the clarification on the drain terminology. Is this the correct hierarchy of drain terminology? The lines under the house are branch lines, these connect to a building drain (located outside the footprint of the house) which then connects to the city sewer.

 

[wwhitney]

I am subject to 2021 UPC.

Texas seems to have adopted the IPC statewide, but the cities can override that, and some have adopted the UPC? Like Houston?

Does the UPC prohibit wet venting a shower downstream of a WC?

Yes, here's the reference for Houston, it basically says the WC has to be last on a horizontal wet vent.

Chapter 9 Vents: Vents, Houston Plumbing Code 2021 | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

But circuit venting doesn't have that limitation. It has other limitations, see this section:

Chapter 9 Vents: Vents, Houston Plumbing Code 2021 | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

It's my understanding that I cannot fall more than one pipe diameter along the shower trap arm before it joins up with the wet vent. I would like to raise it vertically up more than one pipe diameter, so I figured adding the vent to the trap arm was my only option.

Correct.

In terms of vertical pipe runs, should I be thinking of a 60 degree fitting as 30 degree fitting?

Well, it's a 60 degree bend, but if you are vertical and then bend 60 degrees, you will be 60 degrees from vertical, or 30 degrees from horizontal, neither of which meets the IPC/UPC definition of "vertical".

Is this the correct hierarchy of drain terminology?

Going downstream, at least when there's only one building on the property, IIRC it's

Fixture drain -- branch drain -- building drain -- (boundary of the building, or maybe 2ft past it) -- building sewer -- (boundary of the property) -- public sewer

You can find the definition in Chapter 2 of the UPC:

Chapter 2 Definitions: Definitions, Houston Plumbing Code 2021 | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

Cheers, Wayne

 

[Jeff H Young]

The only place a 60 degrre bend can be used as a drainage fitting is vertical but the portion bettween the 2 60s is horrizonal and prohibited so you are kinda screwed. if not for the AHJ I could live with that sin ive had to offset and had to keep it in the wall before.. But its a chance and hassel if called by inspector, and you never know when a inspector gets a kick outta throwing the book at you many wouldnt even know this code

sorry I had other stuff posted here that I removed in regards to another unrelated post

 

[Paul E.]

Thank you for all the helpful info!

After chipping some more concrete and introducing a few street fittings, I was able to land my vent inside the wall using two 45 degree fittings instead of the 60 degree ells.

Wayne, I'm in Austin which has adopted the UPC. Perhaps my WC being upstream may have been OK when this house was built back in 1969...

I am planning on adding a 2" cleanout for this new vent, and then reducing the 2" vent down to 1-1/2" to make routing the vent pipe through the 2x4 walls easier. Ultimately it will rejoin an existing 2" vent pipe via a 2" x 2" x 1-1/2" sanitary tee, oriented for drainage (upside down).

 

[Jeff H Young]

Cool , Just wondering why the capped pipes copper below slab ? im concerned they apear in direct contact with concrete .
The dwv looks good other than a regular 1/4 bend itll be ok just as long as you know who isnt looking but a heads up for next time

 

[Paul E.]

Hey Jeff, thanks for the heads up on the 1/4 bend, I've corrected it to be a 90 degree long sweep.

The copper pipes are in direct contact with concrete. Those are the original water lines for the house. At this bathroom I am running new pex lines in the walls, so I went ahead and capped these abandoned lines.