Venting Bathroom through shower

[Jayjayla]

Hey guys....wondering if somebody can help me out with some DWV stuff. My shower is at the end of my bathroom and I'm wondering if I can vent the entire bathroom off the shower? I guess that would be wet venting the bathroom but I've only seen it done through the lav. Thanks for any info you can provide.

Thanks

 

[wwhitney]

No.

Every trap needs a vent at the elevation of the trap (before the trap arm has fallen one pipe diameter). And with wet venting in a bathroom, you can use a fixture's drain to wet vent a downstream fixture. But there's no way to use the shower's drain to wet vent a lav trap, the drain is just too low.

So that means the lav always needs a dry vent, as its trap is the highest in the bathroom. That's why you see the lav being used to wet vent everything.

You can still dry vent the shower and use it to wet vent the WC. You'll just need to dry vent the lav as well. Those dry vents can combine at any elevation at least 6" above both fixture flood rims.

Cheers, Wayne

 

[Sponsor]

 

[Jayjayla]

No.

Every trap needs a vent at the elevation of the trap (before the trap arm has fallen one pipe diameter). And with wet venting in a bathroom, you can use a fixture's drain to wet vent a downstream fixture. But there's no way to use the shower's drain to wet vent a lav trap, the drain is just too low.

So that means the lav always needs a dry vent, as its trap is the highest in the bathroom. That's why you see the lav being used to wet vent everything.

You can still dry vent the shower and use it to wet vent the WC. You'll just need to dry vent the lav as well. Those dry vents can combine at any elevation at least 6" above both fixture flood rims.

Cheers, Wayne

Ok, thanks Wayne. That seems easy, just set it up how I was describing but go up from a Sani-tee at the lav.
If I can ask one more question. I'm building a small house and thinking about roughing in basically the same bathroom on the other side of the wall so the garage could be converted later. Its a slab so I have to do it now or never. So question is, if I had a back to back bathroom just like this, would you just mirror it and tie all the vents together up high? Since the lavs would need to be dry vented anyway, I assume I could just have a single vent for both of those but would I need separate vents for the two showers since they'd be wet venting the two toilets downstream? Basically, do both bathrooms need separate 2" vents for the shower or can I combine them? My gut tells me to do them separately.

 

[wwhitney]

So you want to rough in underslab DWV to make a mirror image bathroom, flopped across the lefthand wall in your drawing? Which way does the branch drain need to leave the whole area, towards the bottom of the page? And that wall between the WC and the shower, at least some of it is going to be solid, so you can run a vent up through it?

Cheers, Wayne

 

[Jayjayla]

So you want to rough in underslab DWV to make a mirror image bathroom, flopped across the lefthand wall in your drawing? Which way does the branch drain need to leave the whole area, towards the bottom of the page? And that wall between the WC and the shower, at least some of it is going to be solid, so you can run a vent up through it?

Cheers, Wayne

Correct, rough in under slab dwv. Let me sketch it out and re-upload if you're willing to take a look. Thanks Wayne.

 

[Breplum]

I absolutely, always recommend that people hire a licensed plumber for the underslab plumbing. There is way too much to know about how to do every detail correctly and being a slab, so unforgiving and costly to make right.
You cannot rely on an inspector to teach you.

 

[Jayjayla]

I absolutely, always recommend that people hire a licensed plumber for the underslab plumbing. There is way too much to know about how to do every detail correctly and being a slab, so unforgiving and costly to make right.
You cannot rely on an inspector to teach you.

Valid but at the end of the day its not rocket science if you're prepared. I've done it multiple times but its one of those things that I only do every few years so I have to get back up to speed on all the nuances. People on this site have always been a huge help.

 

[Jayjayla]

So you want to rough in underslab DWV to make a mirror image bathroom, flopped across the lefthand wall in your drawing? Which way does the branch drain need to leave the whole area, towards the bottom of the page? And that wall between the WC and the shower, at least some of it is going to be solid, so you can run a vent up through it?

Cheers, Wayne

Not sure how clear my drawing is so I figured I'd answer your questions. Main 3" drain runs basically down the center of the building to pick up the half bath, washer and utility sink on the bottom and the full bath and possible second full bath above. Kitchen is on the far end of the building and is just one 2" sink line/vent.

So yes, just mirror the bathroom for DWV rough in.

The wall between the WC and shower is not solid so the vent would have to be either in the garage wall or the wall into the bedroom.

Thanks Wayne, you've always been such a big help.

 

[Jayjayla]

Not sure how clear my drawing is so I figured I'd answer your questions. Main 3" drain runs basically down the center of the building to pick up the half bath, washer and utility sink on the bottom and the full bath and possible second full bath above. Kitchen is on the far end of the building and is just one 2" sink line/vent.

So yes, just mirror the bathroom for DWV rough in.

The wall between the WC and shower is not solid so the vent would have to be either in the garage wall or the wall into the bedroom.

Thanks Wayne, you've always been such a big help

This is how I would assume it has to be done. Two separate shower drain/vents and two separate 3" branch lines down to the main. If there is a way to simplify it and get rid of one of the separate 3" branch lines that would be great. I think that would be pretty simple with a crawlspace but I'm struggling to think of what fittings I could use to do that horizontally under slab since I don't have much vertical space to stack fittings.

 

[wwhitney]

The main problem with your drawing is that you have a horizontal shower dry vent under the slab. Dry vents can't go horizontal until at least 6" above the fixture flood rim, so that's not allowable. You'd need to route the shower trap arm itself to under or near the wall, so that the dry vent takeoff can be vertical. Vertical includes up to 45 degrees off plumb, so you can use a combo with the barrel rolled up to 45 degrees.

Can I interest you in either a trench drain under the showerhead, or a short section of solid wall (8" - 12" long) between the WC and shower? Either of those would make the shower venting easier. But I'll try to draw up something with a center shower drain and no solid wall.

Also, per breplum's advice, I've never done underslab DWV, just in a crawlspace. So I may not be the best advisor.

Cheers, Wayne

 

[wwhitney]

So maybe something like the drawing below, except that it doesn't show any cleanouts, and adding cleanouts might require rerouting some of the drains. I'm not so familiar with the cleanout rules.

Green is 2" and red is 3". Each shower needs a 2" dry vent so that it can wet vent a WC. A drain for two lavs needs to be 2", although the vent above only needs to be 1.5" (i.e. you could use a 2x1.5x1.5x1.5 double fixture fitting in the wall).

Also, each shower trap arm is limited to 60" of length and 2" of fall before the dry vent comes off. I tried to draw each one so that at the wall you'd use a 45 plus a 22.5 to turn parallel to the wet wall. But maybe it would be better to have one of them start off perpendicular to the wet wall and use a LT90 to turn parallel to the wall.

As I mentioned before, each shower vent takeoff would be a 2" combo with the barrel horizontal (2% slope), and the barrel rolled so that the side entry (dry vent) comes off at 45 degrees from plumb. Then a 45 to turn plumb once under the wall.

Cheers, Wayne

 

[Jayjayla]

Thanks a ton Wayne. I've gotta head out for the rest of the day, I will take a look at this tonight when my brain is working better. Thanks again

 

[Jayjayla]

So maybe something like the drawing below, except that it doesn't show any cleanouts, and adding cleanouts might require rerouting some of the drains. I'm not so familiar with the cleanout rules.

Green is 2" and red is 3". Each shower needs a 2" dry vent so that it can wet vent a WC. A drain for two lavs needs to be 2", although the vent above only needs to be 1.5" (i.e. you could use a 2x1.5x1.5x1.5 double fixture fitting in the wall).

Also, each shower trap arm is limited to 60" of length and 2" of fall before the dry vent comes off. I tried to draw each one so that at the wall you'd use a 45 plus a 22.5 to turn parallel to the wet wall. But maybe it would be better to have one of them start off perpendicular to the wet wall and use a LT90 to turn parallel to the wall.

As I mentioned before, each shower vent takeoff would be a 2" combo with the barrel horizontal (2% slope), and the barrel rolled so that the side entry (dry vent) comes off at 45 degrees from plumb. Then a 45 to turn plumb once under the wall.

Cheers, Wayne

Hey Wayne...so the trough drains are a bit more of a pain to rough in in a slab so that's why I always shy away from them. It seems like I'm always a little bit off even on the center drains but its easy to fix when I build my shower pans. Are you saying that and the little solid wall between the shower and the WC would make it easier because you could just turn vertical with a combo in line?

As for not going horizontal on the dry vent. The way I've done it before based on a plumber friends lead is to basically trench a little lower on the shower trap arm so that the dry vent section can drop into the up turned combo just like you're saying. Then you go horizontal again until you get to the wall where you go up with the LT90. The part that confused me is why it would need to be done under the wall like you said? I guess it can't go horizontal at all so if you turn it up directly under the wall its always vertical? So if we were to do it my way the horizontal leg to the wall would have to be 6" above the shower drain or would it not work at all? Funny that its passed inspection so many times this way. Inspectors are generally useless unfortunately.

Thanks Wayne.

View attachment 92000

 

[wwhitney]

Are you saying that and the little solid wall between the shower and the WC would make it easier because you could just turn vertical with a combo in line?

Just that it would make the trap arm shorter, that's all.

As for going horizontal under the slab--there is an allowance when "structural conditions preclude" the dry vent's staying vertical until 6" above the flood rim level. How that is interpreted varies by jurisdictions.

Prior to the addition of wet venting to the UPC, I would say that would have applied much more often. Now with wet venting I would say it seldom applies. And I would suggest that as my drawings show a method for the dry vent to stay vertical, that means that structural conditions do not preclude in your situation.

Cheers, Wayne

 

[Jayjayla]

Just that it would make the trap arm shorter, that's all.

As for going horizontal under the slab--there is an allowance when "structural conditions preclude" the dry vent's staying vertical until 6" above the flood rim level. How that is interpreted varies by jurisdictions.

Prior to the addition of wet venting to the UPC, I would say that would have applied much more often. Now with wet venting I would say it seldom applies. And I would suggest that as my drawings show a method for the dry vent to stay vertical, that means that structural conditions do not preclude in your situation.

Cheers, Wayne

Thanks Wayne. Simple enough to do it your way, I think its a good option. I appreciate you taking a look.

 

[Jayjayla]

Hey Wayne, I think we're gonna take your advice and explore adding small walls between the WC and shower. The walls would be full height all the way to the ceiling so the vents can go straight up. Do you mind sketching that DWV layout differences? I'm sure you're drawing would be close to what I think it would look like but you always seem to make it more efficient for me.

Thanks Wayne

 

[wwhitney]

Only real difference is that the shower trap arms don't have to go as close to the center common wall, and the vent take off can just be an upright combo with the side branch vertical, as the shower drain passes directly under the stub wall.

You could have the stub wall be a half wall, it just needs to be tall enough for the vent to rise to at least 6" above the shower flood rim so it can turn horizontal to go into the common wall. And the two vents from the two sides could combine as they enter the common wall.

Cheers, Wayne

 

[Jayjayla]

Only real difference is that the shower trap arms don't have to go as close to the center common wall, and the vent take off can just be an upright combo with the side branch vertical, as the shower drain passes directly under the stub wall.

You could have the stub wall be a half wall, it just needs to be tall enough for the vent to rise to at least 6" above the shower flood rim so it can turn horizontal to go into the common wall. And the two vents from the two sides could combine as they enter the common wall.

Cheers, Wayne

That's what I figured, thanks Wayne. We're going to go all the way up with it and wrap the tile around all the way to the end of the bathroom. Then we can make it a standard opening size to get glass cheaper. I appreciate the help.

 

[theroot1972]

Could’ve done this. Easier in my opinion if you have the available drop to the main. Red is drainage. Blue, vent.

 

[Plumb-This-That]

Wayne's post April 22 2023 (about a year ago) included a sketch of how the back to back bathrooms should be piped.
First the water closets should not be the way they're drawn. The water closet should be the first connection to the drain.
Only one fixture should be upstream of the lav in a wet vent. Moving the water closets to take place of the lavs would allow the shower to wet vent through the lav and would put the shower drain in an approved shower trap arm length of less than 5'and would eliminate the need for the 2 shower vents.
In this scenario all that was needed was one 2" vent off the lavs shared by both lavs and wet venting the 2 water closets and 2 showers.