Bathroom group drain/vent advice

[smo0thie]

I am currently remodeling our upstairs bathroom. The current configuration has been modified from the original plumbing (from what I can tell) with the bathtub (will now be shower only) being rerouted with it's own drain and (what looks to me) an illegal dry vent. The installation of the 3" drain that connected with the original 3" vent caused them to destroy the floor joist, which I am in the process of repairing. Here is the existing drain setup:

I am going to reroute the shower drain back with the rest of the shower group and would like to keep the existing vent, but I do believe this is technically an illegal dry vent for the run from the shower 3x3x2 combo back to the vertical vent:

This would save a lot of time by not having to mess with a new vent to the attic. But I am also considering running a new vent downstream of the shower and removing the current 3" vent for a 2" vent:

I am concerned at how this will tie into the vent in the attic, as it will reduce from the 3" vent system down to that 2". Is that allowed with a dry vent? Should I instead go with a new 3" vent in the same location avoid such an issue? The house has a similar vent on the master bath where it runs a short distance upstream of the last fixture drain horizontally before turning vertical so this has swayed my judgement a bit thinking it will be okay. What are your throughts?

 

[wwhitney]

The IPC does not require a 3" vent through the roof. If you get significant frost, it is standard to upsize any vent penetration through the roof to 3" just before the vent leaves the thermal envelope of the building.

Of your 3 diagrams, only the last one shows compliant venting (although it would be more conventional to upsize from 2" to 3" downstream of the shower vent takeoff, rather than upstream).

You could make the second drawing compliant if you reroute the lav drain to go to the right in the wall and hit the 3" stack on the right. That makes the 3" line under the floor a compliant wet vent for both the shower and the WC.

The arrangement in the first drawing could be made compliant by moving the 3x3x2 (or 1-1/2?) san-tee to be below the above floor stack, so that the horizontal jog is in a drain rather than in a dry vent. If necessary due to obstructions, going downstream the 3" stack above the floor could hit a 45 at the subfloor, followed by the san-tee with its barrel at a 45 and side entry pointed to the left.

Cheers, Wayne

 

[Sponsor]

 

[smo0thie]

Thanks for the quick reply! We are in Georgia, so I wouldn’t think frost would be an issue, however 3” pipe is what’s in the attic so I was going to just tie into that. It wouldn’t be an issue for it to reduce from 3” pipe through the roof down to two 2” vent pipes into the wall, would it? I also looked at trying to tie into the 3" vent with 2 45's and the san tee between, with the shower drain floing into that, but I just couldn't seem to get the slope proper and have the hole through the joist at least 2" from the joist edge. So I think option# 2 is what I'm going with. I reduced from 3" to 2" downstream of the shower vent, as you said would be more typical (and cheaper!) Here is the new plan:

I also was just double checking my vent plan in the attic is okay, going from 3" to 2":

Thanks again for the help. I am in the middle of getting the joist replaced as we speak, hopefully I can have this drain figured out so I can install tonight.

Jay

 

[wwhitney]

Thanks for the quick reply! We are in Georgia, so I wouldn’t think frost would be an issue, however 3” pipe is what’s in the attic so I was going to just tie into that. It wouldn’t be an issue for it to reduce from 3” pipe through the roof down to two 2” vent pipes into the wall, would it?

Just like going downstream, a drain may increase in size, going upstream (towards the roof), a dry vent may increase in size.

Here is the new plan:

Looks fine drain and venting wise. For the cleanout, you are required to have 18" clearance from the face of the plug (measured perpendicular), IPC 708.1.10. To the extent that you can roll up the fitting so the plug is above horizontal and still comply with that clearance, my impression is that would be desirable for anyone who has to use the cleanout fitting, less chance of spillage. [And if you don't have 18" of clearance, put the cleanout somewhere else, if one is required.]

Cheers, Wayne

 

[smo0thie]

Well, not sure what to do now. The only reason I was going to install one there was for testing my work. There is definitely not 18” of clearance in any direction. How would you go about testing this?

 

[wwhitney]

Well, not sure what to do now. The only reason I was going to install one there was for testing my work. There is definitely not 18” of clearance in any direction. How would you go about testing this?

Oh, you can install one for a test point, it just won't be a compliant cleanout if one is required. Still could be useful as a cleanout in a pinch. I'm not so versant with the rules on when cleanouts are and are not requrired.

Cheers, Wayne

 

[John Gayewski]

The first picture you posted had a pipe coming from below on the right hand side. What was/is that? Is that something that your getting rid of?

 

[smo0thie]

The first picture you posted had a pipe coming from below on the right hand side. What was/is that? Is that something that your getting rid of?

Yes. It was added sometime later than the rest of the plumbing and I think is the reason they destroyed the joist. It runs to the basement where it picks up the two master bath lavs, which are themselves vented with two AAV’s.

 

[smo0thie]

Oh, you can install one for a test point, it just won't be a compliant cleanout if one is required. Still could be useful as a cleanout in a pinch. I'm not so versant with the rules on when cleanouts are and are not requrired.

Cheers, Wayne

Well that’s good news for me! I do not think it’s required as far as I can tell. Just wanted a place to test my work when done.

 

[smo0thie]

I do think I will have to run the shower drain towards the exterior wall just to get the slope low enough to have the hole through the new joist at least 2” below the top edge and be able to fit the 2” p-trap above the sheet rock. Not something that I thought would be a problem, but I am not a pro. Hoping everything else goes well, the guys are coming back in the morning to patch up the sheet rock and subfloor from the joist repair. Don’t think I’ll be done enough for them to completely close it in, but I really need to get this drain in there.

 

[smo0thie]

Would it be weird to run the shower drain in the opposite direction of the drain for 6 inches, then turn down into the p-trap slightly into the wall cavity below, before exiting the p-trap back towards the drain? I don’t have room below the shower drain to use a 2” p-trap without running the slope at like 2” per foot to get down to the wet vent drain height (which already has a 1/2” per foot slope).

 

[wwhitney]

Not following the issue or question. Note that in the renderings in post #3, the total fall from the 2" trap outlet on the right to the 2" combo that is the dry vent takeoff is limited to 2".

While offsets in the shower tailpiece on the inlet side of the trap are suboptimal, they are allowed and sometimes the best viable option.

Cheers, Wayne