Plumbing A Kitchen Sink Through Cabinet Floor - Not an Island

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by StephanMurray, Feb 9, 2020.

  1. StephanMurray

    StephanMurray New Member

    Joined:
    Feb 9, 2020
    Location:
    Dallas
    Hello,

    I am plumbing a new home on my farm in Texas. The 2 x 6 outside wall, against which my kitchen sink will be located, sits atop a quad 2x12 beam, so there is no way for me to bring a 2" sink drain from the wall directly down into the conditioned crawlspace. Instead, my plan - if you guys approve - is to bring the drain from the crawlspace through the floor of the sink cabinet. At about 16" above floor height, I would use a sanitary tee with tailpiece adaptor to tie into the sink drain. Above the sanitary tee (in approximately the location where the AAV is shown in the diagram below), the 2" vent pipe would 90 degree back into the wall, and then continue through the wall to vent through the roof. Is this allowed - i.e., can I use two 90 degree fittings in order to enter the wall with the vent, since both drain and vent cannot penetrate through the base plate?

    My configuration would be very similar to the diagram below, with the dishwasher as shown. There is a window above the sink that I will need to run under with the vent before turning upwards to the roof. The drain would be shifted more to the right than that shown in the picture to avoid the awkward 45 deg shown in the diagram.

    Would my plan to use 90 deg fittings to bring the vent into the wall be acceptable? How far in front of the wall should my drain be located? What are my options if I cannot bring the vent into the wall due to a code restriction? Would the AAV shown in the diagram then be acceptable, and would this be preferred to a not-per-code wall vent? I am in an area with no code restrictions - rural! - but nonetheless, want to do things the right way.
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  2. StephanMurray

    StephanMurray New Member

    Joined:
    Feb 9, 2020
    Location:
    Dallas
    ((Note, I've reworded my post above in the hopes of making it clearer. I could not figure out how to delete that prior post.)

    I am plumbing a new home on my farm in Texas. The 2 x 6 outside wall on which my kitchen sink will be located bears on a quad 2x12 beam. Because of the beam, there is no way for me to bring a 2" sink drain through from the wall into the conditioned crawlspace.

    Instead, my plan - if you guys approve - is to bring the drain through the floor of the sink cabinet into the crawlspace. At about 16" above the floor, I would use a sanitary tee with a trap adaptor to tie into the sink drain tailpiece. Above the sanitary tee (in approximately the location where the AAV is shown in the diagram below), the 2" vent pipe would angle back to enter the wall (using either 45 or 90 degree fittings). I would then vent through the wall/roof as is usual. Is this an allowable configuration? Can I use the angled fittings in order to enter the wall with the vent, since the drain itself cannot penetrate the base plate and its bearing beam?

    My configuration would be very similar to the diagram below, with the dishwasher as shown and no disposal. The drain would be shifted more to the right (away from the dishwasher) than that shown in the picture to avoid the awkward 45 degree turns shown in the diagram. There is a window above the sink that I will need to run under horizontally with the vent pipe in the wall before turning it vertically to the roof.

    Would my plan to use angled fittings to bring the drain from the cabinet floor back into the wall for venting be acceptable? How far in front of the wall should my drain be located? What are my options if I cannot bring the vent into the wall due to a code restriction? Would the AAV shown in the diagram then be acceptable, and would this be preferred to a not-per-code wall vent? I am in an area with no code restrictions - rural! - but nonetheless, want to do things the right way.
     
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  4. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    You can edit a prior post. If I want one gone, I just replace the content with the word "delete". You might keep some useful stuff when you edit.

    45 is permitted for the vent line, and 90 is not permitted until 6 inches above the flood level of the sink. 45 or less from vertical is considered vertical.

    Right angles that change drainage from vertical to horizontal should be long sweeps. https://www.co.lincoln.or.us/sites/default/files/fileattachments/planning_amp_development/page/722/plumbing_guide_2015_-_helpful_hints_residential_construction.pdf has some helpful info. The choice between black abs and white pvc is largely a regional thing.
     
  5. StephanMurray

    StephanMurray New Member

    Joined:
    Feb 9, 2020
    Location:
    Dallas
    Hello Reach4,

    Thank you for your reply. That answered my question, and the use of two interconnected elbows to get my cabinet-floor drain to vent into the wall works for me.

    Thanks also for the helpful link. I've read it in its entirety, and will definitely be referencing it for my install. My only question regarding this link was in the section on venting in which they stated that the total vent cross sectional area must equal or exceed the cross sectional area of the main sewer line. For a 3" sewer line, this link states that you need two-2" and one-1-1/2" vents to meet the requirement. The IPC seems to use a different approach based on total DFU and vent length. I've got 16 DFU's total in my house (2 bathrooms with toilet, vanity, and tub/shower, 1 dishwasher and 1 kitchen sink, and 1 washing machine). If I'm reading it correctly, the IPC states that a 2" vent not to exceed 120' will handle up to 24 DFU. So, the fact that I have two-2" roof vents should be more than adequate. Correct? I'll post this question separately. Thanks again for your help.
     
  6. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    I think Lincoln County uses UPC, which is more stringent than IPC in many areas. The size of the venting is one of those areas.
     
  7. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Seems to me that you could put the DWV in the wall as normal, and then use a 45 below the san-tee as low as possible to start kicking the drain out of the wall so that it just misses the top corner of the 4-ply 2x12 beam. At the bottom of the wall the 2" drain line would be partially exposed but the kitchen sink cabinet would cover that.

    Would that work? If so it seems easier. You'd drill a hole through the base plate and subfloor at a 45 degree angle.

    Cheers, Wayne
     
  8. StephanMurray

    StephanMurray New Member

    Joined:
    Feb 9, 2020
    Location:
    Dallas
    Hi Wayne,

    It's a thought! I think I might have to start the 45 a little higher up the wall, however, than immediately at the base plate. The reason for this is that my base plate is 5.5" wide (2 x 6) but the beam on which it sets is 6". Shouldn't have to go a lot higher, and I like the thought of having both the drain and the vent in the wall in the standard configuration. Where should I place the stub-out for the kitchen sink - directly in the center, or offset from center and by how much? Thanks for your help.
     
  9. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Not sure on the answer to the last question, someone else may chime in. Often there's a window directly behind the sink, in which case it helps a bit to have the sanitary tee off center, as you'll need to use a 45 on the vent to jog to one side of the window.

    If you have reasonable crawl space access, you can drill your hole from below, that way you can get it up against the girder corner without hitting the girder (it would be OK to hit it 1/4"). To drill at a 45 degree angle with a hole saw, cut a 45 miter in a piece of 4x4 or something, then drill perpendicularly through the slanted face. Now you have a block you can put against the girder or the subfloor with a 45 degree hole in it to guide your hole saw. You can make further cuts in the block to get the hole closer to the corner as required.

    Cheers, Wayne
     
    StephanMurray likes this.
  10. StephanMurray

    StephanMurray New Member

    Joined:
    Feb 9, 2020
    Location:
    Dallas
    Thanks, Wayne. Really helpful.
     
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