Wet vent into toilet from non-bathroom group sink?

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SCKNEU

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Hello all and thanks for any assistance you may provide.

I wanted to add a small wet bar sink to my basement. I planned / installed an AAV for venting. The problem is the drain would have to cross the vent stack from the existing toilet. Initially, I was going to keep that vent horizontal, which was done to fix a leak when the sewer main clogged, but clearly, it's too low as it's below the flood rim and I have to move it up.

It was suggested I could turn the vent from the toilet into a wet vent and therefore not have to cross, so long as I install a cleanout. I wasn't sure if this would pass inspection since the 1 1/2" drain pipe originates from outside the bathroom group. I've read a lot where code references "bathroom groups" but wasn't sure if it was an actual requirement or not? The bathroom vanity is existing and drained separately from the toilet.

My plan was to connect the sink to the wasteline stack that is to the right of the toilet vent pictured but isn't possible without furring out the wall. Maybe that is the answer but I thought I'd check in with you all for any guidance! I've struggled getting guidance from the inspectors here in MD where everything is County based, unlike my experience up North where there is one guy and he can tell you what he wants to see, so again, any help is appreciated!

Thanks!
Scott
 

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wwhitney

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If I understand correctly, the grey pipe coming up through the wall plate is your WC dry vent, which then continues to the right to connect to a dry vent through the roof (and not a stack that carries drainage from a floor above, that would not an allowable vent). While off picture to the right is a drain stack that you could connect the bar sink drain to.

Assuming that's a 2x6 wall, you should be able to pass a 1.5" pipe (bar sink drain, OD 1.9") past a 2" pipe (WC dry vent, OD 2.375") within a stud bay (5.5" deep). Unfortunately, neither pipe could be centered in the depth at the crossing point, but it looks like the WC dry vent is already off center. So if you bring the 1.5" drain through the double stud off center (pull the LT90 towards the camera), then it should be able to cross over the 2" WC vent. You could optionally recenter it in the downstream stud bay with a pair of 45s or 22.5s. Your holes in the stud need to be 5/8" from the face of the stud (or else you need to comply with the notching rules), and so 5/8" + 1.9" + say 1/4" minimum gap + 2-3/8" < 5-1/2". It would be tight.

As to wet venting, horizontal wet venting is only allowed for bathroom fixtures, but what you proposed would be a vertical wet vent. The IPC (in use in MD) calls that "common venting at different levels" and allows it for any 2 fixtures.


However, for that to work, you need to know what fitting is under the floor where the WC vent comes off. Vent takeoffs under the IPC are often done using a san-tee on its back, but a vertical drain hitting a horizontal drain would require a combo fitting. So if you have a combo fitting under the floor, you could repurpose the WC dry vent as a bar sink drain that wet vents the WC; but if you have a san-tee on its back, you'd need to dig up the area to change the fitting to a combo.

Cheers, Wayne
 

SCKNEU

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You are the best, Wayne, thanks!

You are spot on in the description in the first paragraph of a dry vent etc.

I’ll investigate what fitting lies beneath. When fixing the WC vent that someone had previously cut, I could only see that it was an elbow, that you may see from the photo, so I’ll have to get my camera out to see if I can determine how it joins up to the WC?

Thanks for the thorough reply, much appreciated!

Scott
If I understand correctly, the grey pipe coming up through the wall plate is your WC dry vent, which then continues to the right to connect to a dry vent through the roof (and not a stack that carries drainage from a floor above, that would not an allowable vent). While off picture to the right is a drain stack that you could connect the bar sink drain to.

Assuming that's a 2x6 wall, you should be able to pass a 1.5" pipe (bar sink drain, OD 1.9") past a 2" pipe (WC dry vent, OD 2.375") within a stud bay (5.5" deep). Unfortunately, neither pipe could be centered in the depth at the crossing point, but it looks like the WC dry vent is already off center. So if you bring the 1.5" drain through the double stud off center (pull the LT90 towards the camera), then it should be able to cross over the 2" WC vent. You could optionally recenter it in the downstream stud bay with a pair of 45s or 22.5s. Your holes in the stud need to be 5/8" from the face of the stud (or else you need to comply with the notching rules), and so 5/8" + 1.9" + say 1/4" minimum gap + 2-3/8" < 5-1/2". It would be tight.

As to wet venting, horizontal wet venting is only allowed for bathroom fixtures, but what you proposed would be a vertical wet vent. The IPC (in use in MD) calls that "common venting at different levels" and allows it for any 2 fixtures.


However, for that to work, you need to know what fitting is under the floor where the WC vent comes off. Vent takeoffs under the IPC are often done using a san-tee on its back, but a vertical drain hitting a horizontal drain would require a combo fitting. So if you have a combo fitting under the floor, you could repurpose the WC dry vent as a bar sink drain that wet vents the WC; but if you have a san-tee on its back, you'd need to dig up the area to change the fitting to a combo.

Cheers, Wayne
 

wwhitney

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so I’ll have to get my camera out to see if I can determine how it joins up to the WC?
Yes. If you know the route that the WC fixture drain, and the building drain, take under the slab, that could help you in your investigations. I assumed that the WC fixture drain just passes right under that grey fitting coming up through the wall plate, in which case the fitting would be a combo or san-tee on its back.

But it's possible that the fixture drain goes elsewhere, and a wye is used to pull the WC dry vent off, which is carried under the slab to come up through that wall plate. In which case you'd see a 45, 60, or 90 elbow under the floor penetration. For a proper dry vent, a 90 degree elbow would be wrong, but if it's a LT90, that would fine for your conversion to a wet vent. A regular quarter bend would not.

Cheers, Wayne
 

SCKNEU

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Thanks again, Wayne! My sense is, as you suspect, that it is Wye'd into the WC and that the WC dry vent is LT. I've taken a picture from the opposite side of the wall (WC side) and you can see the cast iron curves into the floor as it starts in the middle of the bottom plate and ends near the edge as it goes into the slab.

Thanks for all of your guidance and support - much appreciated!
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