Drain layout for adding double sink to existing bathroom

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AlFal

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Hi All -

With a growing family, I'm looking to replace my existing single sink and vanity (which is conveniently 60 inches wide) with a double vanity and sink. Unfortunately there is only a single existing drain, but thankfully it lines up perfectly with the right side of a double sink. I'd like to add another drain line for the left sink - ideally without having to remove too much wall above where the vanity and sink will be. My current sink drain Tees off of the main stack and then Tees back in above for the vent (I've seen it and taken notes when I had to open up the other side of the wall a year or two ago). I have attached an image of my current layout - labeled existing. I am interesting in knowing if its acceptable to Tee a new drain into the existing waste line as shown in my image Proposal #1. If not, I'm assuming Proposal #2 is acceptable? I'd prefer #1, just because it requires less work in the visible damage range, but if #2 is the only acceptable solution, I'm willing to do it right. Thank you in advance for any guidance -

Al
 

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Terry

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My first question is...........
Is it a vent on the top side? Or is there waste from above going down that stack?
And below, does it continue waste? Or is there plumbing below that is vented with that?

Assuming the first plumber got it right, and the lower part is waste only, and the top part if vent only, then the Second one would work, doing the revents at 42" befor tying back in.
 

AlFal

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Thanks for the response Terry,

The top side is definitely only a vent. This bathroom is on the second floor of a 2 story house. However, I'm not sure about the lower part of the system if its waste only or a shared waste/vent - there is bathroom and kitchen below and I haven't seen how they tie in.

That being said, is #2 still a good plan? It won't make anything worse, right? Even if the lower part is a shared waste/vent.... If that's the case, its been like that for 50+ years.

Regards,

Al
 
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