Adding Second Sink to Vanity

[ManCave]

Hi Everyone. I am looking to add a second sink to my kid's double vanity that currently only has one sink (stupid decision not to just pay for it while the house was being built, I know).

Anyway, here are some pics I took while the house was being built. I believe I have a single 1.5” ABS drain.

From the other “adding second sink” threads that I found searching this forum I need to add a drain/vent like the pic below. Does this look correct? (hard to read some of the notes but the horizontal vent needs to be at least 42" from the floor?)

However, in the spirit of trying to cut the smallest hole in the drywall as possible can I also do it like the picture below – where I run the vent for the second sink straight up to the attic and tie in to the horizontal run in the attic where the existing sink vent goes. Going this route would ideally allow me to just drop in the vent from the attic above thus limiting how large a hole I cut in the drywall (ideally the cut would be lower than the vanity so I don’t have to perfectly patch drywall).

Pic of the existing sink vent in the attic. I think I would need to tie into it somewhere around the area where the vent goes out of the picture. Would that be ok?

Any thoughts or insights would be GREATLY appreciated! Thanks!

 

[Reach4]

1. Is 1.5 drain considered big enough for two lavatories? I don't know if they would permit that in IPC. Maybe join the drains in the crawl space into a bigger pipe? I am not a plumber.

2. On your second pix, if using a santee for a vent tee, you would turn it upside-down from how you posted.

3. You might want to add a cleanout that lets you rod down into the floor.

Nicely illustrated.

 

[Sponsor]

 

[Terry]

By code they like to see 2" when the second lav is added. Sometimes on a remodel you can't do that. Here is one layout that would function.

I've also done this layout with 1.5"

 

[ManCave]

Thanks for your responses!

Our master bath, which we had two sinks put in during construction, was plumbed almost exactly like Terry's second photo using 1.5" ABS. Which is why I assumed a second sink could be added to this setup.

So if I flip the santee on the vent in my first proposed layout would that setup be ok?

What about the second option of running the vent to the attic and tie in to the vent up there? If that setup works is there any special fittings I need to use to tie in to the existing vent?

Thanks so much for your help!

 

[Reach4]

So if I flip the santee on the vent in my first proposed layout would that setup be ok?

What about the second option of running the vent to the attic and tie in to the vent up there? If that setup works is there any special fittings I need to use to tie in to the existing vent?

Yes, both venting proposals would be good. Notice that Terry's first photo shows a cleanout.

Special fittings are not needed, but usually you would need one or more banded (shielded) couplings to tie in. Fernco 3000-150 or Mission CP=150 would be right for 1.5 inch plastic. Hand dishwashing detergent is a good lube to help slide the rubber.

 

[Terry]

Flipping the santee on your first drawing for the vent, yes.
Or you can vent into the attic and revent up there, so many ways it can be done.
You would tie in with either a santee or a wye. Mostly santees for the vents.