Double vanity conversion - opinions requested about drain/vent

[Jfernwright]

Hi there,

Long story short - I'm looking to have a single to double lav conversion re-worked to try to regain some integrity into my load-bearing wall. The plumbers hired by the contractor formerly working on this project mistakenly routed the 2" vent through the 2x4s, when they should have routed it in front (as the drain is). For clarity - the left side will be effectively furred out another 3.5" to make room for medicine cabinets up top, and the drain/vent on the bottom.

I've read many of the threads about this on here, and the implementation I currently have doesn't quite match what I've seen on there, so I'd like some opinions on what I have so I can ensure that the next plumber is setting this up correctly.

My questions are:
- They routed the existing stack all the way over to the left serve the double vanity. Would there have been a particular reason for not teeing off the stack instead? I.e. leave the vent stack complete on the right, and tee the drain and vent into it. Any benefit to one way or the other?
- They used a san-tee. All that I see at the big box stores around here are san-tees, so it makes me think that's just what is used around here. Should I push for a double fixture tee to be used here instead?
- Are the 90s here appropriate for the application. Particularly the one at the bottom where it joins the cast-iron stub with the no-hub fitting. Not sure if the sweep is correct...

I'd definitely appreciate any other comments if anything else looks sketchy with this.

Thanks in advance for your thoughts.


Had to composite the picture - what you're missing in the middle is a wall coming out perpendicular to the wet wall. Also, in case it is useful, the toilet sits directly in front of where the vent stack is/was. A shower is just to the right of this picture. The vent continues up through the second floor wall and exits the roof. So snaking down the vent here will be a challenge...

 

[wwhitney]

First question is whether your plumbing code is UPC or IPC?

There are a variety of ways to do a double lavatory; the configuration used is compliant with both the IPC and UPC, assuming no drainage from the story above. It also would have been possible to leave the 2" stack in place and to run only 1-1/2" drain and vent through your studs to the new double lavatory location. [The UPC would require 3 horizontal 1-1/2" lines (1 vent, 2 separate drains), while the IPC would only require 2 horizontal 1-1/2" lines (1 vent, 1 drain).]

As for elbow sweeps, drainage that is turning to horizontal (from vertical or horizontal) needs a long turn 90. Drainage that is turning to vertical can use a regular 90 (quarter bend). A vent at 6" above the flood rim of the fixture(s) vented can use any 90, including a vent 90.

Also, at the old stack connections, that rubber coupling at the bottom needs to be changed out for a shielded rubber coupling; the unshielded style is only for underground use. And how is the PVC connected to the ABS (?) at the top? That should probably be a shielded rubber coupling as well.

As to your load bearing wall and whether the studs are Swiss cheese, you certainly could replace or sister some studs if you remove all the pipes and cables going through them. In the worst case (which would include any notches for a 1-1/2" or 2" pipe) that's about the only option. For a centered hole for a 1-1/2" or 2" pipe, you can reinforce a single stud with a Simspon HSS2-SDS1.5. If a stud needs 2 of those, not sure if that's a problem. Depending on what load the wall is bearing, there could be a limit to how many studs in a row you can prescriptively reinforce that way without having an engineer design a solution.

Cheers, Wayne

 

[Sponsor]

 

[Jfernwright]

First question is whether your plumbing code is UPC or IPC?

There are a variety of ways to do a double lavatory; the configuration used is compliant with both the IPC and UPC, assuming no drainage from the story above. It also would have been possible to leave the 2" stack in place and to run only 1-1/2" drain and vent through your studs to the new double lavatory location. [The UPC would require 3 horizontal 1-1/2" lines (1 vent, 2 separate drains), while the IPC would only require 2 horizontal 1-1/2" lines (1 vent, 1 drain).]

As for elbow sweeps, drainage that is turning to horizontal (from vertical or horizontal) needs a long turn 90. Drainage that is turning to vertical can use a regular 90 (quarter bend). A vent at 6" above the flood rim of the fixture(s) vented can use any 90, including a vent 90.

Also, at the old stack connections, that rubber coupling at the bottom needs to be changed out for a shielded rubber coupling; the unshielded style is only for underground use. And how is the PVC connected to the ABS (?) at the top? That should probably be a shielded rubber coupling as well.

As to your load bearing wall and whether the studs are Swiss cheese, you certainly could replace or sister some studs if you remove all the pipes and cables going through them. In the worst case (which would include any notches for a 1-1/2" or 2" pipe) that's about the only option. For a centered hole for a 1-1/2" or 2" pipe, you can reinforce a single stud with a Simspon HSS2-SDS1.5. If a stud needs 2 of those, not sure if that's a problem. Depending on what load the wall is bearing, there could be a limit to how many studs in a row you can prescriptively reinforce that way without having an engineer design a solution.

Cheers, Wayne

D'oh - I knew I should have included the code - I'm under the 2015 IPC.

Thanks for the thorough response. It is appealing to me (for the sake of the wall integrity and furring intrusion into the room) to go with 1-1/2" here. For some reason I was thinking the double sinks required the 2" drain.

The PVC is solvent welded to the ABS. Will have that, and the coupling at the bottom replaced with shielded couplings.

I was thinking I am going to have to pull all of the wire and copper in this section as well, sister the studs, then have PEX run back through to replace the copper. And then have the drain routed in front of the existing studs as much as possible with the furred out wall.

 

[wwhitney]

How many studs are drilled for the new PVC, and how many of those are drilled twice?

Pulling out everything and sistering all the studs would be the most thorough repair, but the damage would have to be fairly extreme for justify that. Notching a load bearing stud 2.5" out of 3.5" would count as fairly extreme; drilling a single centered 2.5" hole on a single load bearing stud would be fine to repair with the Simpson HSS2-SDS1.5. Obviously you're somewhere in between, so it will be a judgement call.

If you end up redoing the DWV, then the least invasive solution for the IPC is following: At the left hand lav location, stub out with a 1-1/2" LT90 and start running horizontally at exactly 1/4" per foot. For the right hand lavatory, stub out with a 1-1/2" horizontal combo. Before you hit 6' from the left hand lav trap (so count the portion of trap arm that will be under the sink), put in an upright 1-1/2" combo for a dry vent takeoff. Continue the 1-1/2" drain horizontally to the stack and connect with a san-tee or wye/combo. Extend the vent takeoff vertically to at least 6" above the lav flood rim, then turn the 1-1/2" vent horizontal and run it over to connect to the stack.

If the stack happens to be within 6' of the left hand lav trap, then you don't even need the revent, but the common trap arm has to connect to the stack with a san-tee, and it's important that the trap arm slope be exactly 1/4" per foot. [More precisely the total fall from the trap to the vent connection may not exceed 1-1/2", while the trap arm must fall at least 1/4" per foot.]

Cheers, Wayne

 

[Jfernwright]

There are effectively 4 studs drilled @ 2.5". 2 of those notched at about 50% (where the old copper drain was). 2 notched to 75% for this new work.

The left-most lav stubs out at 6 feet from the stack, so looks like the revent is required here.

I *think* I follow what you've outlined (it's very clearly described, I just don't have my head entirely wrapped around venting whys and wherefores). One thing not clear to me in the revent option is why the tie in to the stack can be either a san-tee or a wye/combo. Is it because the revent provides all the venting needed at that point?

Thanks!

 

[wwhitney]

One thing not clear to me in the revent option is why the tie in to the stack can be either a san-tee or a wye/combo. Is it because the revent provides all the venting needed at that point?

Precisely. In fact, with the revent option, you could in fact omit the stack between where the common drain turns downward and where the revent ties back into the stack. That portion is not doing anything, it's no longer part of the vent path of either fixture.

Sorry if I'm repeating myself (there are multiple threads on double lavs at the moment), but this all assumes that there is no drainage coming down the stack from the floor above.

Cheers, Wayne

 

[Jfernwright]

Sorry if I'm repeating myself (there are multiple threads on double lavs at the moment), but this all assumes that there is no drainage coming down the stack from the floor above.

lol - yeah, I've been keeping up with those other threads too. (Was scratching my head about the difference in 2 lavs needing a 2" drain in another thread, vs the 1-1/2" we're talking about here... Then I noticed it was UPC vs. IPC here.)

No - no drainage from above. I'm pretty sure though that this stack does vent the shower (upstream) and toilet (downstream). Not sure if that makes a difference.

 

[Jfernwright]

@wwhitney - I think I have sketched what you were describing below. Does this look about right?

Was also considering this (scale is off, but it shows the gist). Not sure if there is any real benefit for the extra pipe though. Would this be a viable option as well?

 

[wwhitney]

First drawing, yes,

If you don't mind the extra holes in the studs for the second drawing, that version dry vents both lavs, so many would consider it a better option. I think I agree.

[BTW, if the 3-way fitting in the middle bottom you labeled "LS" is meant to be a combo (for long sweep), then its side entry is actually past the end of the barrel. Drawing it that way differentiates it from a san-tee.]

Cheers, Wayne

 

[Jfernwright]

First drawing, yes,

If you don't mind the extra holes in the studs for the second drawing, that version dry vents both lavs, so many would consider it a better option. I think I agree.

[BTW, if the 3-way fitting in the middle bottom you labeled "LS" is meant to be a combo (for long sweep), then its side entry is actually past the end of the barrel. Drawing it that way differentiates it from a san-tee.]

Cheers, Wayne

Great - thanks. Will likely shoot for the second option then. I think I can avoid a lot of holes since I'm furring out the sections in play here.

And, thanks for the tip on the drawing - appreciate your attention to detail!