(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 13 of 13

Thread: Double vanity plumbing options

  1. #1
    DIY Junior Member nawyner's Avatar
    Join Date
    Dec 2012
    Location
    Georgia
    Posts
    5

    Default Double vanity plumbing options

    Hello everyone, I'm sorry for posting another double vanity question, but this forum truly is the best place to go for all things plumbing related and as I am not a plumber this was the best place to go. I have been able to find answers to all of my questions so far…which leads me to this one…which happens to be my first post. I think I have it figured out but I would like to make sure I am thinking about it correctly. I live in Georgia and our plumbing code our county uses is the International Plumbing Code. I am doing a guest bathroom remodel on a house built in 1970 which originally had one vanity initially installed in the guest bathroom, but it was also plumbed with the sink from the master (on the left side, other side of the wall). I want to convert this right side single sink set up to a dual vanity set up. The total number of fixtures on this 3 in vent line are at most three (there is on downstairs sink that may be vented) and once the new sink added would be four.

    The way I see it there are three options,

    Option 1: just hook up the drain from the new sink to the existing drain line. (I think this is incorrect b/c of siphoning issues with the other sink, but since this would be the easiest option I wanted to see if I was missing something.)

    Option 2: Hook up the drain from the new sink to the existing drain line and then run a 1 ½ vent line straight up through the roof.

    Name:  P1090101-option 2.jpg
Views: 2437
Size:  55.7 KB

    Option 3: Hook up the drain from the new sink to the existing drain line and then connect into the stack (see picture).

    Name:  P1090101-001.jpg
Views: 885
Size:  57.2 KB

    I think option 2 and/or 3 would meet code but I’m not sure, also any other ideas/options would be very helpful. Thanks again

    Jason

  2. #2
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,653

    Default

    None of your options meet code, and ALL could cause siphoning of one sink or the other. #2 and #3 are exactly the same and could siphon the left hand sink because of water flowing past its connection without a vent. To do it correctly, you would have to insert a new tee lower than the existing one, then either pipe both sinks to it, using a back to back fixture fitting, or the new sink into it using the piping design from either 2 or 3 with a tee in the vertical riser.
    Licensed residential and commercial plumber

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,405

    Default

    You can't run waste past another trap without it being separately vented...once a drain, always a drain. Once a vent, always a vent, you can't mix them together.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    DIY Junior Member nawyner's Avatar
    Join Date
    Dec 2012
    Location
    Georgia
    Posts
    5

    Default

    Thanks for the advice so far, I really appreciate it. I've redone some of the drawings so please check them out. The first two correspond to the two option of what I think HJ was describing above. The third option was to raise both sink drains and tie back into existing drain. The fourth option ties into existing drain but inserts a vent in between the two sinks. Do these options meet IP code? Also am considering redoing the entire cast iron stack upward w/ pvc since it would be relative easy to do. Final question, when attaching pvc to existing cast iron on a vertical run such as this are the shielded fernco's (the one's completely encased metal) the best way to attach the pvc to cast iron? If so where would be the optimal place to cut and attach.

    Thanks again,
    Jason

    Name:  new option 1.jpg
Views: 624
Size:  54.3 KBName:  new option 2.jpg
Views: 628
Size:  55.2 KBName:  new option 3.jpg
Views: 638
Size:  56.9 KBName:  one more option.jpg
Views: 621
Size:  51.7 KB

  5. #5
    Test, Don't Guess! cacher_chick's Avatar
    Join Date
    Jan 2008
    Location
    Land of Cheese
    Posts
    3,150

    Default

    The 2nd and 3rd pictures both work.
    Which one will work for you will depend on how high the trap arm coming off the sink will be.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,405

    Default

    Placement and design is a dance...some of it depends on the height and configuration of the vanity (drawers, shelves, etc.) AND the depth of the sink. Then, you have to work around existing plumbing. Since you have to put the trap under the sink, and the trap arm needs to go into the drain without going up, there will be some height that becomes too high. Some people are using kitchen cabinet height vanities (nominally 36") verses the old standard of 30" or so - that can make a big difference on where your trap arm can go.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    DIY Junior Member nawyner's Avatar
    Join Date
    Dec 2012
    Location
    Georgia
    Posts
    5

    Default

    I think I will go with the third option (raising the drain height). We are going from our old vanity height of 30" to our new vanity height of 35" so that gives me at least 5" + to work with so I'm thinking that is the way to go. If I do go that option and tie a pvc T into the existing cast iron what would be the best way to do that? I'm sure I will have to use a fernco couple (likely the shielded one). Would it be better to cut at the hub or above the hub of the cast iron? Thanks again.

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,405

    Default

    They make donuts to transition to pvc that go into the hub. Not all CI hub sizes are anything but standard, so they make lots of sizes of donuts. Get the wrong one, and it's a pain to insert (hard to compress the stiff rubber), or it's loose and leaks. If you have enough room, and the pipe is in good condtion, (cutting CI can shatter pieces in bad condition) then a no-hub (shielded) fitting is the proper way to do it.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  9. #9
    DIY Junior Member nawyner's Avatar
    Join Date
    Dec 2012
    Location
    Georgia
    Posts
    5

    Default

    Thanks for the response. THe CI seems to be in pretty good shape. So I'm thinking cutting it would be ok without it disintigrating. If I go that route, what would be the best way to secure the CI pipe, riser clamps? One final thought, instead of doing the option we discussed, what about running a 1.5 in vent line between new sink and original sink up to the attic and placing a studor vent on it? What would be the pros and cons of that. It would be a simplier install. Thanks again for your help it is great to bounce different ideas off of experienced pro's.

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,405

    Default

    There are special clamps designed to anchor CI. They need to be attached to solid framing. The connection from CI to pvc (or abs) is with a no-hub connector (reinforced banded rubber sleeve). Inspectors will usually not approve the use of an AAV when a viable atmospheric vent is available - IOW, I doubt they'd approve its use in this application. Plus, the extreme heat in a place like Georgia in the attic is likely to destroy the air seal, and then you'd be leaking sewer gasses into the attic which isn't good, either.

    Adding a vent in between the two, depending on how it was done, could still leave the original one improperly vented. The 'break' or vent has to be between the trap arm and where it attaches to the drain - you can't run waste past the trap arm without it being vented at that point.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  11. #11
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,653

    Default

    #1 and #2 are correct, but the horizontal drain line will be 2" pipe, (there are NO 1 1/2" double fixture fittings). #3 would raise the drains so high you would not likely be able to connect to the sinks properly and the line would have to be changed to 2" anyway because of the fixture fitting. #4 is just a variation of your original "improper" drains, and as Abraham Lincoln once said, "You can call a dog's tail a leg, but he will still only have four legs". Doing #3 will raise the drain openings at least 6 or 7 inches, (you would have to measure the "center to center" dimension when the double fitting is placed on a "long sweep" elbow. Your "vent tee" would have to be inserted at least 42" above the floor so that eliminates any discussion about where to make the cut, relative to the hub.
    Last edited by hj; 12-11-2012 at 05:32 AM.
    Licensed residential and commercial plumber

  12. #12
    DIY Junior Member nawyner's Avatar
    Join Date
    Dec 2012
    Location
    Georgia
    Posts
    5

    Default

    Forgive me if this sound like a stupid question, but what if in my last option, I were to move my vent to the right side/or equal with the new sink drain (it was my initial second option), would that not be circuit venting and would that not be acceptable?

  13. #13
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,405

    Default

    You cannot run waste past a trap arm without it being vented at that point, or if you try, you'll siphon it dry. So, look at how the waste is flowing, where you're connecting things to it, and see if the vent is in the proper position.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

Similar Threads

  1. Need options for plumbing db vanity into 3" vert. drain/vent
    By sidac99 in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 1
    Last Post: 04-28-2012, 03:00 PM
  2. Advice on proposed double vanity plumbing
    By jagermeister in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 0
    Last Post: 01-20-2012, 03:38 PM
  3. Converting single sink vanity to double vanity
    By xceebeex in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 4
    Last Post: 11-28-2011, 09:22 AM
  4. Plumbing a double vanity
    By moose186 in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 12
    Last Post: 11-13-2010, 07:15 AM
  5. Plumbing Double Vanity (Remodel): Please Check My Plan
    By tlyoung99 in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 2
    Last Post: 05-13-2010, 07:06 PM

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •