Basement Bathroom Group Wet Vent

[herynkc]

I current have what is pictured installed for a bathroom group in a basement (toilet, lav, shower). These are tieing directly into the main 4" drain under the basement slab. There is a 3" main vent stack conveniently located just downstream of the toilet (this is a dedicated 3" dry vent for the main drain line). I was hoping I could use this 3" vent for my entire bathroom group. I know the toilet is currently sufficiently vented, however I still question whether the lav and the shower need a dry vent of their own in addition? I am used to dry venting all my fixtures.

Can I leave the current installation as is and consider my lav and shower drains as wet vented via the 4" main drain line? or do I need an auxiliary dry vent on them for proper function? Most bathroom group schematics I am seeing add a dry vent to atleast the lav, however they dont have a 3" main vent stack nearby. My setup is a bit different

Where is the "vent opening" considered when wet venting? and does this still need to be higher than the trap weir? I am a bit confused on this aspect of wet venting.

We use UPC here in Oregon.

 

[Daniel Collick]

I current have what is pictured installed for a bathroom group in a basement (toilet, lav, shower). These are tieing directly into the main 4" drain under the basement slab. There is a 3" main vent stack conveniently located just downstream of the toilet (this is a dedicated 3" dry vent for the main drain line). I was hoping I could use this 3" vent for my entire bathroom group. I know the toilet is currently sufficiently vented, however I still question whether the lav and the shower need a dry vent of their own in addition? I am used to dry venting all my fixtures.

Can I leave the current installation as is and consider my lav and shower drains as wet vented via the 4" main drain line? or do I need an auxiliary dry vent on them for proper function? Most bathroom group schematics I am seeing add a dry vent to atleast the lav, however they dont have a 3" main vent stack nearby. My setup is a bit different

Where is the "vent opening" considered when wet venting? and does this still need to be higher than the trap weir? I am a bit confused on this aspect of wet venting.

We use UPC here in Oregon.


View attachment 93380

I reserve the right to be wrong, but this configuration wouldn’t pass inspection nor would I pipe this type of configuration from a practical standpoint.
If it’s never caused a problem, I can see why and that’s awesome, but I don’t think I’d leave it this way.
The 3” vent may have been overprotection due to the 3” drain being piped into your level 1 bathroom group configuration.
1. The 3” main drain should be piped downstream from your bathroom group configuration.
2. You can wet vent your whole level 1 bathroom group using a 2” pipe as long as it’s done properly.
One way would be:

 

[Sponsor]

 

[Daniel Collick]

I reserve the right to be wrong, but this configuration wouldn’t pass inspection nor would I pipe this type of configuration from a practical standpoint.
If it’s never caused a problem, I can see why and that’s awesome, but I don’t think I’d leave it this way.
The 3” vent may have been overprotection due to the 3” drain being piped into your level 1 bathroom group configuration.
1. The 3” main drain should be piped downstream from your bathroom group configuration.
2. You can wet vent your whole level 1 bathroom group using a 2” pipe as long as it’s done properly.
One way would be:

In the configuration I provided, once you pipe your water closet you don’t have to reduce down to 2” for your wet vent, but 2” is sufficient. If you have a 2x6” plumbing wall I’d keep the wet vent 3” just until the clean out, so a 3” clean out tee with a 3x2” bushing for your lav/wet vent, the shower would then be a 3x2” fitting, even if it’s a tub it will drain better.

 

[herynkc]

In the configuration I provided, once you pipe your water closet you don’t have to reduce down to 2” for your wet vent, but 2” is sufficient. If you have a 2x6” plumbing wall I’d keep the wet vent 3” just until the clean out, so a 3” clean out tee with a 3x2” bushing for your lav/wet vent, the shower would then be a 3x2” fitting, even if it’s a tub it will drain better.

Thanks for your reply.

What do you mean by "overprotection"? There was no bathroom group here originally. I have added all that is pictured, aside from the original 4" drain. Also note that the main drain is 4" not 3"

I appreciate you sharing your drawing, however I cannot really read it due to the very small size.

 

[wwhitney]

Basic answer: assuming the stack (vertical pipe at least one story tall) on the upper left of the picture is carrying drainage from a story above, then the configuration shown is a no go. For wet venting a bathroom group, the drains serving as wet vents can only carry drainage from within that bathroom group. Which doesn't happen when each fixture joins the 4" building drain separately, and so as shown you'd need to dry vent each fixture before it joins the 4" building drain.

So what you could do (schematically, and perhaps also physically) is to reroute the drainage from the stack at the upper left around your new bathroom group, and have it rejoin the existing 4" building drain only downstream of all 3 bathroom fixture. Then to wet vent the bathroom group, your layout is fine if you provide a 2" dry vent (for the UPC) on the lavatory (whose drain is already 2").

This assumes the distance along the drain from the shower trap arm to that wye where the lav joins the 4" line is no more than 60" and falls no more than 2", and that the distance along the drain from the closet flange to the 4" wye is no more than 72". If you actually did this in practice, rerouting the 4" drainage from above around the right side of the shower, I'd suggest downsizing the bathroom group 4" line upstream of the 4" wye for the WC to 2".

Is that 3" stack at the lower right really a vent? Nothing draining down from a story above at all? There's no real reason any such stack would be installed, unless it was installed by an earlier builder for the purpose of adding a bathroom group there.

But if so, then you can take the 2" dry vent off your lavatory and route it up into the basement ceiling and connect it to that vent stack. If the 3" stack is not a vent (what I would expect) and you have no other dry vents in the basement, then you'll need to take the 2" dry vent off the lavatory up at least one story to find an existing 2" dry vent that you can tie into at least 6" above the fixture flood rim level of any fixtures served by that vent.

Cheers, Wayne

 

[herynkc]

Basic answer: assuming the stack (vertical pipe at least one story tall) on the upper left of the picture is carrying drainage from a story above, then the configuration shown is a no go. For wet venting a bathroom group, the drains serving as wet vents can only carry drainage from within that bathroom group. Which doesn't happen when each fixture joins the 4" building drain separately, and so as shown you'd need to dry vent each fixture before it joins the 4" building drain.

So what you could do (schematically, and perhaps also physically) is to reroute the drainage from the stack at the upper left around your new bathroom group, and have it rejoin the existing 4" building drain only downstream of all 3 bathroom fixture. Then to wet vent the bathroom group, your layout is fine if you provide a 2" dry vent (for the UPC) on the lavatory (whose drain is already 2").

This assumes the distance along the drain from the shower trap arm to that wye where the lav joins the 4" line is no more than 60" and falls no more than 2", and that the distance along the drain from the closet flange to the 4" wye is no more than 72". If you actually did this in practice, rerouting the 4" drainage from above around the right side of the shower, I'd suggest downsizing the bathroom group 4" line upstream of the 4" wye for the WC to 2".

Is that 3" stack at the lower right really a vent? Nothing draining down from a story above at all? There's no real reason any such stack would be installed, unless it was installed by an earlier builder for the purpose of adding a bathroom group there.

But if so, then you can take the 2" dry vent off your lavatory and route it up into the basement ceiling and connect it to that vent stack. If the 3" stack is not a vent (what I would expect) and you have no other dry vents in the basement, then you'll need to take the 2" dry vent off the lavatory up at least one story to find an existing 2" dry vent that you can tie into at least 6" above the fixture flood rim level of any fixtures served by that vent.

Cheers, Wayne

thanks for your reply.

I just attached another photo documenting what I ended up doing. (I have not installed the new trap for the shower just yet, but there will be one.)

Both the shower and lav now are dry vented to above. The toilet is still relying on the the 3" dry vent (and yes it is truly just a 3" dry vent, I have 100% verified that there is absolutely nothing draining into this stack.)

The stack on the upper left of my originally posted photo is indeed carrying drainage from the 1st floor above. Now you've said "drains serving as wet vents can only carry drainage from within that bathroom group," - Do I really need a whole separate dry vent for this toilet as well? Currently the amount of wet vent would be merely a 12" distance on that 4" main drain line. Seems overkill to me.

 

[wwhitney]

Your shower dry vent is a problem, because it goes horizontal at an elevation lower than 6" above the fixture flood rim. [Also, the takeoff requires a combo rather than a san-tee on its back, and your takeoff is pointed the wrong way, the idea is to let water drain out if water backs up into the vent.]

There's an exception in the UPC allowing the lower horizontal vent when "structural conditions" preclude complying with the minimum height [which exception would require a LT90 at the wall where the vent turns up], but it predates the allowance for wet venting, so I would expect that with wet venting, the exception is much less available and would not apply. And also if you have any framed wall within 60" of your shower trap, you could route your shower drain under that wall to pull off your dry vent, so that would presumably also preclude using the exception.

On the WC dry vent, assuming the 3" stack is less than 72" along the drain from the closet flange, to dry vent the WC what you are supposed to do is keep the WC drainage separate from the 4" building drain, use a combo to takeoff the 3" vent vertically, and only then connect the WC drain to the 4" building drain.

In case my earlier textual description wasn't clear, below is what I was talking about in terms of wet venting the bathroom group. Blue is 2", Red is 3", and Orange is 4". The blue line drawn at the upper left is really supposed to be in the ceiling.

I'm not sure this is necessarily the best idea; for example if you have enough depth under the slab to stack two layers of pipe, you could do the same thing but sending the 4" building drain under the bathroom drains, eliminating the extra turns in the 4" building drain. Since you seem to have enough height to send the shower dry vent over the 4" line, what you could do is instead send the shower drain line over the 4" line, then all your fixtures are on one side of the existing 4" building drain path, and you can do your bathroom wet venting on that side, and use the existing 4" wye where the WC connects to the building drain to instead connect the whole bathroom group. Note that the maximum drop from the 2" shower trap outlet to the wye where it joins the lav and gets wet vented is 2", but between that wye and the wye where the WC joins, the 2" line could pitch downward as required.

Cheers, Wayne

 

[wwhitney]

Since you seem to have enough height to send the shower dry vent over the 4" line, what you could do is instead send the shower drain line over the 4" line

Illustrating this option below, if you have the height to pass the 2" shower drain over the 4" building drain. The drop from A to B is limited to 2", and the pipe run to 60" in length, as that is your shower trap arm. The drop from B to C is not limited.

Or you could possibly change your shower drain layout to get the trap on the other side of the 4" building drain. E.g. a linear drain against the foundation wall, with the outlet on the left side of the picture.

Cheers, Wayne

 

[Jeff H Young]

Illustrating this option below, if you have the height to pass the 2" shower drain over the 4" building drain. The drop from A to B is limited to 2", and the pipe run to 60" in length, as that is your shower trap arm. The drop from B to C is not limited.

Or you could possibly change your shower drain layout to get the trap on the other side of the 4" building drain. E.g. a linear drain against the foundation wall, with the outlet on the left side of the picture.

Cheers, Wayne

View attachment 93393

He looks plenty deep to cross back over main as wayne drew this up

 

[herynkc]

Illustrating this option below, if you have the height to pass the 2" shower drain over the 4" building drain. The drop from A to B is limited to 2", and the pipe run to 60" in length, as that is your shower trap arm. The drop from B to C is not limited.

Or you could possibly change your shower drain layout to get the trap on the other side of the 4" building drain. E.g. a linear drain against the foundation wall, with the outlet on the left side of the picture.

Cheers, Wayne

View attachment 93393

Many thanks for all your suggestions and feedback.

If starting fresh, the most labor and cost effective method wouldve been wwhitney's second suggested schematic. However at this point it involves cutting open the main 4" drain again. I did not want to get into this as it would be a real pain to get it re-aligned as both ends are fixed against concrete. I know I would need to use either use a fernco or rebuild half that upper stack if I did so.

My solution was running the shower vent into a small fin wall adjacent to the shower at a little higher than a 45deg angle (as shown in my sketch below) then tied back into the lav vent above.

I have not added or modified anything with the toilet setup at pictured, as it seems really unlikely to pose any issue given that there is a 3" dry vent immediately 12" downstream. I know technically you're not supposed to do this since the very short wet vented portion of that air path is used for drainage of upstream fixtures outside of the bathroom group, but will it really pose any issues?; the toilet is going to get enough air and since everything else is sufficiently vented I would not see any issues along the lines of trap siphonage. What would be the main concern for relying on this current 3" vent for the toilet?

 

[Jeff H Young]

itll probebly be ok but I wouldnt find out Id have to change it . wouldnt feel comfortable with that violation