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I'm a DIY-er with a lot of experience in some phases of construction but not much in plumbing (so please be nice to my dumb questions!). I'm finishing a basement with a full bathroom, and thought I'd toss out a question here as I ponder whether to attempt myself or hire out.

My question is about venting. When they built the home 2 years ago, they roughed in for a bathroom in the basement. I'll put a picture below of the rough in. In the picture, numbered 1 to 3 from left to right, is a drain pipe for the lav (it is right up against the insulation), then the toilet, then the drain for the tub. But, I can't find any evidence of a vent. There's no rough in for a vent in the ceiling anywhere, and the lav drain is just capped off and doesn't extend upward to a vent (as I would have expected). The only stack in the vacinity is 3.5 feet to the right from the tub drain, but I know it is draining the 1st floor laundry (and possibly others as well). Any ideas on how to vent this without having to run a new vent to the roof (which would be near impossible)?

I think my local code allows AAV venting (as I'm pretty sure my kitchen sink has one, though the other bathrooms in the house do not). However, even if I did that for the lav, what about the toilet and tub? Is it at all possible that the stack draining the laundry could be used as a wet vent for any/all of the basement bathroom fixtures? (I'm thinking no, but thought I'd ask.)

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  • What is a "lav" in this context? (In British English it is a very informal abbreviation for "lavatory" == "toilet", but that clearly isn't it.)
    – Martin Bonner supports Monica
    Jun 10, 2019 at 14:22
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    My understanding is "lav" (at least in American English) is used in plumbing circles to refer to a sink basin.
    – stekun
    Jun 10, 2019 at 15:33
  • Thanks. Makes sense, a lavatorium was a place to wash.
    – Martin Bonner supports Monica
    Jun 10, 2019 at 19:55

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With new construction the vent is probably in the wall, you would not be able to see it, it is probably tied into the upstairs vent and may not be a straight shot up, with the home being only 2 years old you should be able to get the blue prints for the plumbing layout and they will show the layout, I would not be concerned because the plumbing would not have been approved prior to the floor being poured without a vent.

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  • Makes sense. I'll look into getting the blue prints to verify. When you say "in the wall" though, do you mean in the cement? Other than the insulation that is tacked onto the cement, there are no other walls, so I would have thought a vent stack would be either visible or at least hiding behind the insulation. At any rate, it sounds like I just use AAV to vent the lav trap and call it good then?
    – stekun
    Jun 10, 2019 at 15:35
  • I have put vents & plumbing in concrete walls many times it is more common than having them out in the open.
    – Ed Beal
    Jun 10, 2019 at 15:39
  • Great, thanks! For some reason I thought I remembered them pouring the foundation, including walls, before they roughed-in the basement plumbing, so I didn't even consider the possibility that the vent went through the concrete. Thanks for clarifying that for me!
    – stekun
    Jun 10, 2019 at 16:59

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