Help on adding drain

[Chris57]

need to install a second drain for a double vanity. I'm under the IPC. House was built in mid 80s.
My current drain looks like the following:existing
......................................................vent
.........................................................|
.........................................................|
........................................................ |
t0 house drain ------------A---------S------------R
..........................................................<---21"----->
..........................................< -17"-->
R is a right angle out of the wall for existing single sink drain
S is a sanitary Tee to vent, 21" from existing drain
A is where I need to add a new drain, ~ 17" prior to vent
The existing horizontal pipe is sloped down to house drain
Pipes are 1.5"PVC

What is the best way to add a drain at location A?
Advice is appreciated! Just want to do this as correctly as possible without tearing the house apart!

Chris

 

[Reach4]

I made the attached sketch before you posted your photo.

 

[Sponsor]

 

[Chris57]

thanks! I didn't think the photo would be that useful until I saw my diagram needed formatting.

 

[wwhitney]

To properly answer your question, you need to know how all the other fixtures in your bathroom are vented, and the size of the pipes in the photo.

If the pipes in the photo are 1.5", and if the lav goes on to wet vent a tub, a shower, or a WC, then you have a problem. An IPC 1.5" wet vent can only carry the drainage of 1 DFU (1 lavatory). So at the point the second lavatory joins in, the wet vent needs to increase to 2" in diameter. Meaning you'd have to replace all the existing 1.5" drain downstream of the new lav until you reach a point where it's already 2".

[An unlikely further downstream issue is that a 2" wet vent is limited to 4 DFUs. So suppose the lav is wet venting a shower with multiple shower heads totaling over 5.7 gpm so that it counts as 3 DFUs, and then the 2" wet vent continues from there to wet vent the WC. If you add another lav, the wet vent carrying 2 lavs and the 3 DFU shower is now carrying 5 DFUs, and you'd need to upsize the drain between shower and WC to 3".]

But if the lav isn't wet venting any fixtures, or if the pipes in the photo are already 2", adding a lav is easy. The existing lav can wet vent the new lav, so you just need to cut in a combo where you want the new lav. Since both ends of the pipe are fixed, you'll need two banded rubber couplings, e.g. Fernco 3000-22 or Mission CP-200 for 2" plastic to 2" plastic.

Cheers, Wayne

 

[Chris57]

Thanks Wayne! I think other things have their own vents but not sure. Will try to figure it out.