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Thread: another Single Vanity to Double Vanity thread, IPC

  1. #1
    DIY Junior Member tekmassa's Avatar
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    Default another Single Vanity to Double Vanity thread, IPC

    I've read the previous posts regarding this conversion, and I'm hoping to get some expert advice on my specific problem. I'm converting my master bath single vanity to double vanity, and the new double vanity has drawers in the middle preventing me from using a common drain on a single p-trap (that would've been too easy). Please see the below photo of my current (less than impressive) plumbing:



    The cutout section is between two studs, and the 2" drain is right up against a stud. The vent goes straight up the wall and to the roof from here. I have no idea what the 3/4" PVC duct-taped to the 2" drain pipe is for??

    I'm looking at two potential ways to get where I need to be to have two drains for my two sinks.

    Option #1 - 45 degree bends to allow use of double fixture sanitary tee


    Option #2 - stacked sanitary tee


    I will need to go through the stud on the right side with both the drain and supply lines for the second sink. My two questions:

    #1 - What is the 3/4" PVC for? It comes out of the slab and goes straight up, but does not exit in the attic.

    #2 - Which of my two options is the better choice? Are both bad?

    Also, any additional concerns/considerations?

    Your advice is greatly appreciated!

  2. #2
    Plumbing Designer FloridaOrange's Avatar
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    Option 1 looks fine in my book.
    I would guess the 3/4" PVC is for condensate, do you have an AHU above nearby?
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

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    DIY Senior Member asktom's Avatar
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    Option 1 - You are using a double san tee, it should be a double fixture tee. You won't find one with a 2" barrel and 1 1/2" branches, you would need to get a 2" and put bushings in the branches.

    Option 2 - If you turn the elbow on the right out of the wall rather than going up and then out you will be fine (if not symmetrical), assuming the bottom of the trap will clear the cabinet. By going up and then out you take the vent out of play, which is not legal and creates a situation where the trap may siphon.

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    DIY Junior Member tekmassa's Avatar
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    Quote Originally Posted by FloridaOrange View Post
    I would guess the 3/4" PVC is for condensate, do you have an AHU above nearby?
    Nope, the AHU is on the complete opposite end of the house. The only thing I can think of is that our old water heater had the pressure relief valve tied into a pipe going into the wall that has since been capped. The water heater is on the other side of that wall approx 10 ft. down.

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    DIY Junior Member tekmassa's Avatar
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    Quote Originally Posted by asktom View Post
    Option 1 - You are using a double san tee, it should be a double fixture tee. You won't find one with a 2" barrel and 1 1/2" branches, you would need to get a 2" and put bushings in the branches.

    Option 2 - If you turn the elbow on the right out of the wall rather than going up and then out you will be fine (if not symmetrical), assuming the bottom of the trap will clear the cabinet. By going up and then out you take the vent out of play, which is not legal and creates a situation where the trap may siphon.
    It sounds as if Option #2 may be the best bet, going straight out instead of up and out for #2. I will need to measure twice to make certain the opening in the back of the vanity will accommodate the outlets at both heights. I was unsure if stacking the two san tees as I had was acceptable or not.

    Thanks!

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    Nuclear Engineer nukeman's Avatar
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    Quote Originally Posted by tekmassa View Post
    I was unsure if stacking the two san tees as I had was acceptable or not.
    Our code (IPC based) allows it, but there is a restriction on the number of DFUs from the upper fixture drain.

    See Section 908.3: https://www2.iccsafe.org/states/Virg..._Frameset.html

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    Forum Admin, Expert Plumber Terry's Avatar
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    Option 2 is not legal.
    Turning the drain upwards creates an S trap.
    If you are considering wet venting one teel over the other, the vertical would need to be a 2" pipe.


    In UPC plumbing, option 1 would need a double fixture fitting, not a sancross.

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    DIY Junior Member tekmassa's Avatar
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    Quote Originally Posted by Terry View Post
    Option 2 is not legal.
    Turning the drain upwards creates an S trap.
    If you are considering wet venting one teel over the other, the vertical would need to be a 2" pipe.


    In UPC plumbing, option 1 would need a double fixture fitting, not a sancross.
    If I go with option #2 I'll be sure not to turn the drain upwards.

    Regarding the double fixture fitting, would I be able to find this at my local big box retailer (Home Depot/Lowes)? Would it be labeled as a "double fixture fitting"?

    Thanks everyone!

  9. #9
    Moderator & Master Plumber hj's Avatar
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    The drain does NOT have to directly behind the sink's opening, so you should be able to put the back to back fixture fitting in the vertical riser, and then offset back to the sink inside the cabinet.

  10. #10
    Forum Admin, Expert Plumber Terry's Avatar
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    Here is an example of a double lave with an offset.
    2" to the bottom of the fixture fitting, the rest of the pipe is 1-1/2"


  11. #11
    DIY Junior Member tekmassa's Avatar
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    Ok, I have two follow up questions. I cut out a larger section of drywall to do all the work today and made two interesting (to me, at least) discoveries.

    First, the 3/4" PVC pipe I was puzzled by in my original post, seems to just end a few inches up. It's not capped, and I have no idea what it is for? From the lack of obvious stench, I don't believe it's connected to the drainage system. It's just sticking up from the slab right next to the 2" drain.



    Secondly, the copper water supply lines (1/2") have a 12" long 3/4" extension, that go nowhere. They're capped and the only thing I can think of is that they were put there to allow them to be affixed to the studs for support? I plan on running the lines through the studs on the left and right, so they'll be supported by the studs. Anything I should be aware of before removing these 3/4" capped extensions?



    Again, thank you all for your advice!

  12. #12
    Forum Admin, Expert Plumber Terry's Avatar
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    The copper 3/4" pipes with caps are water hammer chambers meant to prevent water hammer.
    They tend to fill up, so we use mechanical hammer arrestors now. But since this is for a lav, we don't normally install them there anymore.
    It's for a "quick closing" valve.

    The 3/4" PVC, it could be for a p-trap that needs priming, or it could just be extra.
    Pretty strange.

  13. #13
    Moderator & Master Plumber hj's Avatar
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    The PVC may just be a "stake" to secure the 3" pipe in position while the concrete was poured.

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