(Another) Single to double vanity - best way to reroute pipes?

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Savedsol

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My second one of these threads. :)

We're redoing the master bath and are replacing a rotted out single vanity with a double sink. My issue is the piping (waste and supply) all comes from the side and not behind.

Here's the scheme vanity we ordered: http://ancerre.com/backend/products/category_file_D/20150624055744.pdf

My thought was to just add a 2x3 wall in front of the existing (outside) wall and route - pretty tightly - the waste, vent and supply around that corner into the new false wall. The wall where the existing plumbing is is not load bearing; but behind it is a tub where we're doing a tub to shower conversion and were planning to add a ginormous, sectioned niche (drawn green box). All plumbing is 1 1/2".

Based on my previous single to double (with the help of this site) I understand the vent/waste need. I'm just wondering if I'm making this too difficult on myself with the false wall idea (plan 1) and if I should just butcher the vanity and come in from the side (plan 2) since the drawers in the middle are not full width. These niches and the litany of piping in the side wall have thrown us for a loop. For what it's worth the bathroom is on the second floor with the kitchen below. I don't want any more drywall work than I already have but if rerouting from below the floor is the better option I could, begrudgingly, be persuaded.

Thanks,
Matt
 

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Cacher_Chick

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The vent coming up from downstairs is serving another fixture, so it cannot be eliminated.

The new sink vent can be routed up higher than the niche, so there is no problem there. If you move the supplies out of the corner, you should be able to fit the drain and vents there.
 

Savedsol

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Thanks for the quick reply. Just to be clear, I wasn't going to terminate the other vent. The plan (I tried to illustrate in "View 2 Plan 1) was that I'd cut it low and run it around the niche.
To clarify your comment, are you suggesting that building that false wall (plan 1 in photos) is the way to go - Cut the supply lines low and bend everything 90 degrees into the fake wall?
 

Cacher_Chick

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It depends on how much room there is in the back of the vanity, maybe the piping would fit behind the drawers and you do not need a false wall at all. Either way works.

Edited to add- To keep from going into the exterior wall with the vent, the false wall is a fine plan.
 
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Savedsol

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Good deal - glad to hear I've got a semi decent understanding. Here's the top down scheme of the vanity. Looks like 6" behind the drawer. I'll have to query the better half on these two plans.

Neither plan was incorporating going into the exterior wall (I'm not a masochist! Ha!) so hopefully we're both on the same page since I didn't think a new vent was needed with plan 2 - just using the common one in place... and routing it around the niche.
 

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Cacher_Chick

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The vent needs to rise at least 6" above the flood rim of the sink before it turns horizontal as correctly shown in "plan 1 view 1".

In many places, it would not be permitted to wet vent the second sink drain as shown in your "plan 2".
 
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Savedsol

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Thank you. If you could please humor me, did the code change? I ask as the previous single sink just dumped into that drain - no separate vent rise above the sink overflow. Cheers!
 

Savedsol

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If it helps, I'm under IPC 2012 and the Illinois State Plumbing Code (no Pex... grrrr). I've attached another thought/plan to run by y'all - just in case since it would be the simplest. I've seen this site recommend the double fixture tee in similar circumstances but since the vent is not up the middle I'm wondering if that makes this a non-starter.

Much appreciated in advance.
 

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Cacher_Chick

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The problem is that you are not understanding how a trap and it's vent works. It is not permitted to allow waste from one sink to flow past the connection from the second sink unvented.

If you properly utilize a double-fixture fitting, the vent riser must come off the top of it, and it must be vertical until it rises at least 6" above the flood rim of the fixtures.
 

Savedsol

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Ok - totally understood. My brain was trying to make sense of "how it was" and come up with as lazy of a solution as possible (hence plan 3 where they share the double fixture). Thanks cacher_chick for all of the help - false wall it is. It was plan 1 - so you know I was on the right track... just scheming. ;)
 

Terry

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The original plumbing was revented at 42", which is 6" above flood.
Your drawing 2 had what we would call S traps, or non-vented. The vent is above the trap arm, not below.
The vent can tie in again, as long as it's above the flood level. That would be the top of the sink on the counter.
 
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