Waste pipe location for double vanity remodel

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by stephenson, Feb 4, 2013.

  1. stephenson

    stephenson Member

    Messages:
    76
    Location:
    Northern Virginia
    So, I have cabinets totaling 8' with two vanities. Left to right: 12" drawers, 30" vanity, 12" drawers, 30" vanity, and 12" drawers. Complete remodel on an outside wall with double end plates (2x10) so can't run drain in walls ...so, need to do P trap and run to 90 down into floor inside the vanity.

    My question relates to placement of rough drain stub ...where, left to right, should I put the stub? Since I have to P then run horizontal (prob will use AAV) then down into the joist bay, should I offset the stub to the left side of the vanity opening on the sink on the right, and right side of the sink on the left ...or the same in both (I have lots of space underneath floor). I was thinking offsetting would ease the transition from P to the 90 into the floor.

    Does this approach seem reasonable ...any alternative vent option - cant use the wall and there is about 12' between sinks and closest vertical vent.

    Thanks!
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,032
    Location:
    Cave Creek, Arizona
    I have absolutely no idea HOW you intend to run the drains or if it is even a proper way to do it. You do not say if this sink setup is replacing an existing one or if it is a new location. However, since you have to ask the question, it is very possible that this is not a good DIY problem for you. I have NEVER had an installation where I could NOT use the wall, but that may be the difference between me having done it for 60+ years and this being your first one.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,262
    Location:
    New England
    With the two sinks that far apart, you'll need a p-trap and vent for each. Without knowing what's overhead, there's no way to tell how best to vent them. The fact your existing vent is 12' away has little bearing on whether that is a viable tie-in point or not.
  4. stephenson

    stephenson Member

    Messages:
    76
    Location:
    Northern Virginia
    Thanks, Jim,

    I have vent stack through the roof about 12 feet away ...and, yeah, I can take a vent up through the exterior wall, but it would be a pita ...I MAY even be able to run a vent line in the floor and connect it up to the stack. AAV would be a lot easier, though.

    Hj, for a moderator, you don't sound very moderate.
  5. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,259
    Location:
    Land of Cheese
    An atmospheric vent must be vertical until it is at least 6" above the flood rim of the sink, so "under the floor" would definitely be a bad choice. The basins will need to be separately trapped and the drains could be combined with a double-fixture fitting. How and where everything will fit given your array of cabinets and drawers cannot be guessed properly here given what you have told us.
  6. stephenson

    stephenson Member

    Messages:
    76
    Location:
    Northern Virginia
    Sorry, didn't mean to infer would put AAV in floor, but that I have 12" available in which to run vent line. The vanities and drawers all in line, but must take drains through floor vice wall since double plates on exterior wall ...since sinks in line I should be able to just go straight down and follow one another into the same drain with wyes.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,032
    Location:
    Cave Creek, Arizona
    quote; I MAY even be able to run a vent line in the floor and connect it up to the stack

    ANY vent line "in the floor" would violate all plumbing codes if it were for the lavatories. My role as moderator, in my opinion, is to tell people when they are exceeding their level of incompetence.

    quote; since sinks in line I should be able to just go straight down and follow one another into the same drain with wyes.

    As I tell my wife, quite often. Your solutions to problems are simplistic, and do not take into consideration situations in the real world. Your "solution" would work, but so do a lot of the solutions installed by DIYers, even though they are "marginal" and possibly "illegal". "Double plates" under a wall is the reason your cabinets have a "toe space" under them.
  8. stephenson

    stephenson Member

    Messages:
    76
    Location:
    Northern Virginia
    I am attaching a very basic diagram - probably should have started with this. I converted it from a pptx to a jpg so hopefully it will be somewhat readable.

    HJ - I just don't understand the negativity - I'm trying to ask for help and maybe I'm not asking the questions accruately, but I want to try and do things right. I am a pretty proficient guy at most things, including having done a bit of plumbing, electrical, building, rebuilt engines, flown airplanes, concrete, laid tile, etc ... I try and research and ask questions, and ... I could pay others to do the work, but I like doing what I can for myself - when it is possible - yeah, it makes me feel good to do something with my hands. I may indeed end up asking a qualified plumber to either do the work or assist me (so I can learn). So, if you can be helpful, please respond. If you can't, hopefully others will try and be helpful like Jim and cacher_chick were.
    Last edited: Feb 6, 2013
  9. stephenson

    stephenson Member

    Messages:
    76
    Location:
    Northern Virginia
    Made a modification, deleted the original diagram and added this one. Thanks.

    Attached Files:

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