Adding second drain for double sink vanity, check my design?

[Rugz31]

Hello all. I'm going to attempt my first major plumbing project soon (other than replacing galv lines with PEX) and need some advice or input. I've been researching and reading as much as I can on here to avoid having to make another post like this, but some advice I was recently given has me rethinking everything.

I need to add another drain line for a double sink vanity, currently only have one drain and it's centered. I will need to move the drains to the left and right of where the drain currently sits. The current drain pipe is 1 1/2" so that will need to be changed to 2" to support a second lav. Current plumbing below.

This is the design I was planning to use, but someone told me I'm planning to do more work than I need to. Is this the correct way to plumb this, or is there an easier way that I'm not seeing? The other guy told me I should do something called a horizontal common vent, which would meet IPC code and involves less work.

This is a 1 story house with cement slab foundation in Houston, TX, if that makes any difference.

 

[Bob Y.]

Hello,

Do not use PEX RED and BLUE water lines as they will leak in time. They also get brittle and could crack in years to come. I will NOT use them if you paid me to use them. PEX water lines are rather new, and they have been known to leak at the fittings in walls.

Please stick to what works, the old tried and true thick-wall COPPER water lines. If copper pipes are soldered correctly, they should last for 75 to 100 years and beyond without any problems. When soldering copper pipe, please be sure to use lead-free solder.

For the drain pipe, PVC is a good choice to use. You should use a 2" vent pipe instead of a 1-1/2" vent pipe. All sink rough-in drain pipes should be 2 ". Once again, use PVC for all drain applications.

I hope this is helpful to you. If you have any further questions, please contact me.

Bob

 

[Sponsor]

 

[Rugz31]

Thanks for the advice, but it's not really what I was looking for. I'm trying to find out if my proposed drain/vent layout is the correct design, or if there's an easier way. I've seen threads on here where people post a similar design to what I'm proposing, but I was recently told by someone else the revent line to tie back into the 2" vent stack is unnecessary. They said the trap arms off the main 2" drain at bottom will vent fine and is acceptable under IPC. I'm trying to find out if that guy was right or if he's wrong.

 

[Reach4]

Thanks for the advice, but it's not really what I was looking for. I'm trying to find out if my proposed drain/vent layout is the correct design, or if there's an easier way.

Your way works, and there may be an easier way.

I've seen threads on here where people post a similar design to what I'm proposing, but I was recently told by someone else the revent line to tie back into the 2" vent stack is unnecessary. They said the trap arms off the main 2" drain at bottom will vent fine and is acceptable under IPC. I'm trying to find out if that guy was right or if he's wrong.

I am not sure what you are describing there, but I expect is is not OK. You could sketch that out too. I am not a plumber.

 

[hj]

Just use elbows at the top and bottom. You do not need the Tees. Your PEX is fine. I might not use it, but that is just my preference, not based on any facts.

 

[Rugz31]

Your way works, and there may be an easier way.



I am not sure what you are describing there, but I expect is is not OK. You could sketch that out too. I am not a plumber.

I think this is the general idea of what he was saying I should do, excuse my very crude drawing. He called it a "horizontal common vent" but it just doesn't look right to me, and I'm not sure what type of fitting I'd need to connect the trap arms to accomplish it. He said the upper vent line from the double fixture tee back to the 2" stack was "superfluous and unnecessary" but it was a Reddit plumber so I'm taking it with a grain of salt.

HJ, is there anything wrong with using the san tees at the top and bottom? I already purchased them, but can easily exchange them if need be.

 

[Reach4]

I think this is the general idea of what he was saying I should do, excuse my very crude drawing. He called it a "horizontal common vent" but it just doesn't look right to me, and I'm not sure what type of fitting I'd need to connect the trap arms to accomplish it. He said the upper vent line from the double fixture tee back to the 2" stack was "superfluous and unnecessary" but it was a Reddit plumber so I'm taking it with a grain of salt.

I think you did not understand what he was suggesting. I don't know what he was suggesting, but it was not that. You will find "common vent" in https://wabo.memberclicks.net/assets/pdfs/Plumbing_Venting_Brochure_2018.pdf

 

[Rugz31]

Then I'm just going to put that out of my mind. I know he specifically said I'd be adding an unnecessary vent. Either he didn't understand what I'm trying to do or I'm too dumb to understand what he was trying to tell me.