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Thread: non-island loop vent

  1. #1

    Default non-island loop vent

    Have a dual bowl kitchen sink with disposal centered beneath a bay window, which prevents me from using a traditional vent as the window is 40" above FFF so I cannot make 6" above the rim before the vent would need to turn horizontal. Seems the only options are AAVs (no thanks) or a loop vent.

    I cannot use a dual fixture fitting to serve both sinks because there is an electrical outlet blocking the central vent. Also, due to a thick old foundation wall immediately below the kitchen, there is no room for the usual below-floor horizontal leg of the vent or for that matter the 45 elbows and wyes that connect the loop to the drain.

    Shown below is my proposed solution.

    Questions:
    1. Is a loop vent permitted in other (non-island) installations?
    2. Can this all be enclosed in an exterior wall?
    3. OK to have the horizontal vent tie-in above the floor?
    4. OK to have the drain and loop connect to the 2" drain using Sanitary tees on the flat?
    5. OK to have the horizontal portion at the top of the loop vent instead of the usual 90 degree elbow peak?

    Thanks in advance and I'd appreciate any simpler or superior alternatives.

    Name:  kitchen vent.jpg
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  2. #2
    Moderator & Master Plumber hj's Avatar
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    My experience has been; Yes to #1,2, and 3. NO, to #4 and 5. The "central vent" does NOT have to be in the exact center. Why the "drip leg" on the 2" main vent? You also need a cleanout on the drain line itself, not just the vent.
    Last edited by hj; 10-31-2013 at 06:57 AM.
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  3. #3

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    Thank you for your reply to this and to all the other discussions I've been reading.

    The drawing shows just part of the main vent (and waste) as it comes up from the basement and continues upward (no drip leg).

    As you point out I could use an off-center dual fixture fitting and thus have a single vent and do a traditional loop vent from there... solving #5. Will also add a cleanout.

    Still stuck on #4 though. Would Sanitary tees on the flat be allowed if they were just drains and not part of a loop vent?

    The window is 68" wide and the sink is right in the middle... a 45 degree vent won't clear the window and a dirty arm would be pushing length...and I was hoping to retain individual traps for each bowl.

    Racking my brains here...

  4. #4
    DIY Senior Member asktom's Avatar
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    Simple is best. If you can use one trap and a dirty arm 42" or less I think that is the way to go.

  5. #5

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    Quote Originally Posted by asktom View Post
    Simple is best. If you can use one trap and a dirty arm 42" or less I think that is the way to go.
    I agree that simplest is best. But I just measured and the dirty arm would be more than 42". I don't think there is a perfect answer, so as much as I dislike doing so, I think it's going to come down to picking the lesser of all evils... dirty arm would be too long (window width), loop vent can only be tied to the drain with san tees on the flat (foundation wall), and vertical vent will turn at 40" (window). I'm leaning towards this last choice as the best of what seems possible.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    The sanitary tees are illegal WHEN they are part of a drain, it has nothing to do with being part of a loop vent. And since the "main vent" also serves the basement yours would have to tie into it at least 42" above the floor. Otherwise it becomes an "alternate drain path" if the regular horizontal drain plugs up.
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  7. #7
    DIY Senior Member asktom's Avatar
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    2" trap arm?

  8. #8
    Moderator & Master Plumber hj's Avatar
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    4' to 5' unless his code is different.
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  9. #9

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    I sure do appreciate everyone's time and thoughts on this.

    Here in Baltimore City we are under NSPC 2009. In regards to vent, 12.6.2 states vents shall rise min of 6" above flood level of the rim of the fixture "before connecting to another vent" but has two exceptions:

    -loop vents for island sinks
    -horizontal portions of a vent below the floor level that a) have the invert of the horizontal portion of the vent is at or above the centerline of the horizontal waste pipe, b) drains by gravity back to the drain, and c) has clean outs so blockages in the below-flood portion can be cleared into the drain.

    Reading closely, I can do #2! It seems to allow for my strongly preferred and simple dual drain setup:
    Name:  simple.jpg
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    Drains are all 2" but turn 90 to be horizontal just below the floor and then 45 into wyes into the 2" drain to the stack.

    I'd rather not do the loop but this is what it would look like:
    Name:  loop.jpg
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  10. #10
    DIY Senior Member asktom's Avatar
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    In your top drawing the vents of the two traps are tied together too low. If one side clogs up there is an alternate way for it to drain - via the vent to the other side.

  11. #11
    Moderator & Master Plumber hj's Avatar
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    There is absolutely no benefit to using the loop in the second drawing if you can install it like the upper one. Since the two vents are tied together right under the window framing, the sinks would be full of water before the vent could become a "secondary drain". Therefore, someone would be aware it was happening, (unless they liked having a sink full of water all the time), and the only side effect would be that that sink could not overflow. But, if you can install the drains as in your second drawing, with a "double fixture fitting", WHY would you not do so with the first drawing and eliminate the second drain riser and vent? That would also eliminate any problems caused by the two vents. Or do you have some kind of compulsion that makes you want to have two risers in the wall, regardless of what they are? Another possibility, but it might be beyond the scope of a DIYer might be to run the single vent in 1 1/2", use 1/6 bends to angle the vent, starting just above the sink's sanitary tee, and adjust the location of the riser so the angled vent clears the lower left corner of the window. This is my method quite often when I have a situation like that, such as in my current residence. Depending on the specifics of your location, I might also angle the combos up and into 45s just below the floor, to make a better flowing drain.
    Last edited by hj; 11-02-2013 at 08:28 AM.
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  12. #12

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    ..."sink full of water"... ..."some kind of compulsion"... Have you been in contact with my wife? She hates it when I let the pots soak.

    I much prefer the non-loop configuration and will go with that, including rolling the combos as much as I can and using 45s as you suggest. The reasons in my head for two risers are 1) lowest likelihood that one sink would ever flow into the other; 2) the holes in the framing already exist (this is all to fix a previous non-vented install); 3) there is a stud just to the left of the right hand riser; 4) vague feeling that combining them later with 14" between the tees would yield better capacity/lower likelihood of clogs than doing so with the dual fixture, and would outweigh the potential problems with two vents. Reasons #2 and #3 are obviously not a big deal and that last one may be pure voodoo.

    I thought 45 degrees was the delineation between what's considered horizontal versus vertical, and since I cannot clear the LL corner of the window at 45 degrees, I sent the vent up and then over. If you believe a continuous slope from above the sanitary tee to above 42", even if it's a shallow angle (say 22.5 degrees) is better, I can do that.

    Final (?) version (although looking at it, it does make two risers seem ridiculous):
    Name:  final.jpg
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    Transition from sloped to vertical vent would be above 42". Need cleanouts on the vent(s)?

  13. #13
    Moderator & Master Plumber hj's Avatar
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    No cleanouts on the vents, but one on the right hand drain line below the sink's tee. Doing it "twice" is "dumb" as you have seen once it is drawn out. If the drain plugs up it will be in the horizontal section, and probably past the second tee, so the two sinks will still flow into each other. All you are doing is making a lot more work for yourself.
    Last edited by hj; 11-03-2013 at 10:54 AM.
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  14. #14

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    I'm going to turn both vents 60 at the same elevation above the tees and send them over past the window, and then turn them up as soon as possible (was not thinking clearly last night... they don't need to be above 42" before going vertical). Then once they are higher than 42", wye them together, go up a bit more and the turn 90 to tee them into the main vent. Cleanouts are the black circles. I finally like it. Any thoughts?

    Name:  finalfinal.jpg
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    Edit: just read your edit... thinking....
    Last edited by douglasgb; 11-03-2013 at 11:34 AM.

  15. #15
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    Quote Originally Posted by douglasgb View Post
    I'm going to turn both vents 60 at the same elevation above the tees and send them over past the window, and then turn them up as soon as possible (was not thinking clearly last night... they don't need to be above 42" before going vertical). Then once they are higher than 42", wye them together, go up a bit more and the turn 90 to tee them into the main vent. Cleanouts are the black circles. I finally like it. Any thoughts?

    Name:  finalfinal.jpg
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    Edit: just read your edit... thinking....

    Just run 3" under the sink and waste stack vent it
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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