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Thread: venting dilemma

  1. #1
    Nuclear Engineer nukeman's Avatar
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    Default venting dilemma

    I'm currently doing some work on the basement bathroom. I am relocating the shower drain a few inches for these reasons:

    1. increasing shower size and moving drain will keep it centered
    2. you really hear water in the drain when a toilet upstairs is flushed. I believe the venting to be inadequate

    When I first opened the walls, I found these two stacks with the cleanout buried behind the drywall. The lav is 1.5" copper and tees into the 2" CI tee. Around 5' or so above the floor, the piping transitions to copper. My first thought was this 2" line was wet venting the bathroom group. Okay..no problem. However, you can see from the drawing that I did that I have a major fixture discharging past this unvented shower drain. The 3" stack that is near the condensate line receives discharge from 2 WCs, 2 lavs, and a shower/tub combo.

    So, the next thought is just do a dry vent for the shower and connect 6" above the flood rim of the lav into that 2" line. However, it turns out that 2" "vent" is also the drain for a pair of lavs on the 2nd floor (not sure why they didn't use the nearby 3" for the 2nd floor lav drains). I know that having a wet vent between different floor levels is not code here.

    I could turn that 2" wet vent into a dry vent by draining the two 2nd floor lavs into the 3" line, but that would be down the road when I renovate the 2nd floor bath. Running a new vent to the attic would be very difficult is it would have to run from the basement on a two storey house. There is a dry vent at the kitchen sink above this area, but again that would require tearing up the kitchen walls to tie into the vent.

    AAVs are legal here, but would prefer a normal vent. I just don't know if there is a easy way to do so.

    Could I come up and tie into the 2" above the flood rim of the basement lav (6") using a tee and maybe putting a AAV on the tee? I know the AAV needs to have ventilation and be accesible. Then when I turn that 2" into a true dry vent, I can remove the AAV and plug off that part of the tee to make a normal vent.

    I don't know if this makes sense. I can try to add some more pics or diagrams if something is not clear.

    Thanks!

    Kent
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    Last edited by nukeman; 11-23-2009 at 07:14 PM.

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default Dwv

    I hope that "P" trap is at a shower or floor drain, otherwise it is in the wrong place. IF the noises you hear are due to venting, which is unlikely, an AAV will do nothing to prevent it. Even revising the venting the way you describe may do nothing to relieve the symptoms.

  3. #3
    Nuclear Engineer nukeman's Avatar
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    Thanks, hj. I realized after I posted that I didn't label that pic. Yes, this is the shower drain. As you see, it goes down to the p-trap and then straight into the horizontal main line.

    I don't know if the p-trap is being sucked dry. I haven't looked real close yet. The shower has not been something that we used (believe it or not, the surround was made of metal and the bottom where it met the pan was all rusty). I really only noticed the noise when I was working down there and a toliet upstairs (one where the water will pass the shower) flushes.

    There had been some smell down there (not strong), but the trap may hae been dry due to no use. I have since filled the trap a couple times. I don't notice any smell now, but the walls and doors have been opened up, so maybe the smell doesn't concentrate.

    I know that it is a no-no to discharge a major fixture passed an unvented one like this, so I would like to add a vent to this shower drain. Maybe it'll help the noise and maybe not, but at least it should be better. The other issue I guess is that the floor drain and condensate drain are setup like a combination drain/vent, but I understand that the horizontal line needs a dry vent somewhere to make this legal and there are no dry vents currently connected at the basement level.

  4. #4
    Nuclear Engineer nukeman's Avatar
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    Here is what I was thinking in case the text wasn't clear. I know this setup would work just fine (and be code) if I wasn't receiving discharge from the pair of lavs on the 2nd floor (and the AAV wouldn't be needed). my reasoning for the AAV is incase water flowing from the lavs upstairs causes problem in venting the basement shower. When I renovate the 2nd floor bath (maybe in a couple years), I can convert that 2" to a dry vent by draining the lavs into the 3" line. At that time, the AAV could be removed and where it screwed into plugged.

    On the 3" and 2" stacks, there is an offset at the top of the basement wall. This is because this load bearing wall is cinder block in the basement and there is standard wood construction above this. The offset is there to allow the pipe to run between the studs on the floors above.

    Thanks,

    Kent

    Edit: Should be 4" on the horizontal run..but you get the idea.
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    Last edited by nukeman; 11-25-2009 at 05:52 AM.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Default vent

    I am not sure what you are trying to show, but if you intend to install that horizontal section now, you cannot as long as the pipe is an active drain. Whether an AAV will help or is necessary depends on many factors which are not apparent in the drawing or pictures.

  6. #6
    Nuclear Engineer nukeman's Avatar
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    Sorry. Red dashed line is the proposed 'vent' to be added to the shower drain. Besides the red line, the rest of the plumbing is existing. What else do you need to see? Most everything is under the slab, so it is limited on what I can show in terms of pics.

    The main problem that I see with the current plumbing is the discharge of a major fixture past the unvented shower. The 4" horizontal cast in the last drawing receives the following upstream of the shower connection:

    - 1 WC and 1 lav on 1st floor
    - 1 WC, 1 lav, 1 tub/shower combo on 2nd floor
    - condensate in basement (very minor flow, of course)

    I'm just trying to to things correctly here. I really do not want to tear up the walls on the two floors above to add a new vent line. I figure that the AAV can take over as the vent until I convert that 2" into a dry vent. You do bring up a good point, though. If I tie into that 2", I may be in trouble since I am modifying the existing plumbing and would likely have to bring it up to current code. Hmm...

    I have no dry vents at the basement level where I can tie into. The only options that I can think of:

    - run what is in the drawing, but may have to revise that drain to turn into a vent
    - run a new vent to the roof. Would require tearing up walls in the 1st and 2nd floors
    - tie into the vent for the kitchen sink. Would require tearing up a wall on 1st floor
    - just run a AAV. Would require tearing up the bathroom again to use a standard dry vent in the future

    The vent (or AAV) may or may not help the noise in the drain, but it couldn't hurt and would be at least the right way to do things. My understanding is that I have to vent that shower branch since currently there are several major fixtures discharging past it.

    Anyway, I am trying to get the info that you guys need. Just let me know what isn't clear and I can get additional pics or diagrams.

  7. #7
    Nuclear Engineer nukeman's Avatar
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    I've looked into it a bit more. I filled the shower trap yesterday and now it is dry. I also noticed some bubbles in the shower p-trap when the toilet on the floor above is flushed. I am almost 100% sure it is being sucked dry due to poor/no venting. Then when the trap is dry, you really hear the water draining from other fixtures as it passes the shower. I'm just not sure why there isn't more of a smell if the trap is dry..

    The other possibility is there is a leak in the p-trap. I have not pulled the p-trap out yet as I wanted to pick up a plug and get some new fittings and start playing with some ideas on the layout. The current plumbing is 40 years old.

    I think that I will propose that red dashed line for the venting and see if that'll fly. If not, maybe I can just use the AAV.

    I have another question: is it okay to use a p-trap which contains a union under the slab? I was looking at the fittings at HD the other day and for a 2" p-trap, they only have one in PVC with a union on it.

    Thanks, guys. Hope you had a nice T-day.

  8. #8

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    If you intend on installing an AAV such as a Studor Mini then why bother connecting into the vertical stack? Just make the AAV accessible and forget the horizontal vent run.
    http://www.inspectpa.com/forum/forum.php
    My answers are based mostly on the ICC codes. Advice given is my personal opinion and every person performing work should acquire a permit from his/her jurisdiction and get the work inspected. My opinions are not directions to follow for DIYs or professionals

  9. #9
    Nuclear Engineer nukeman's Avatar
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    The horizontal connection is for the future. When I renovate the 2nd floor bath, I can drain those lavs into the 3" line and that 2" will become a dry vent. At that time, I could ditch the AAV and drywall over the AAV access panel.

    I don't have personal experience with AAVs. It seems like a lot of plumbers don't really like them and some people complain about the noise they make. I have to see what the inspector will let me do. That 2" stack is acting as a wet vent for the basement lav and doesn't meet current code. So, if I tie into that line, I may have to bring it up to code. In this case, I'll just toss the AAV on there and forget the horizontal portion of the vent.

  10. #10
    Nuclear Engineer nukeman's Avatar
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    I seem to have a couple problems here:

    1. The wye where the shower connects into the 4" main line is about 16" away from the closest wall and about 27" away from the location where I want to bring the vent up. The line is about 15" below the slab, so I can't maintain 45* or greater slope and still make it to the wall. The closest wall (about 16" away) might work, but that wall is currently a cinder block wall with 2x2 furring strips, so no room for a vent. I could build it out to make a wet wall, but I would have to push the oppoite wall out a bit to maintain room for the 48" shower I want to use.

    2. It looks like the washer standpipe is not vented. It is on the other side of the wall, basically across from the lav. Looks like they were counting on wet venting that through the lav. This is a load bearing wall, so I imagine the standpip runs under the footing and connects into the 4" main.

    3. I could possibly move the wye for the shower closer to the lav so that I could bring the vent vertically up that wall. I would like to avoid this option if possible as I don't really want to cut/splice the 4" main, but I will if it is the only option.

  11. #11
    Nuclear Engineer nukeman's Avatar
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    I'm leaning towards option 3 as I just don't seem to have the room to make this work. Basically, I will remove concrete above the main line towards the lav. Then connect the shower drain at that spot and run the vent up (AAV or to the roof if I can manage).

    Question:

    - Current connection is a CI wye with the shielded bands on all connections. If I ditch this shower connection, can I simply block off the 2" part of the wye and just leave it or do I need to pull the wye and add some kind of coupling in its place?

    Thanks!

  12. #12
    Nuclear Engineer nukeman's Avatar
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    Closing this out. Here's what I did:

    - replaced a section of the 4" CI under slab with PVC and used proper Fernco couplers to attach new PVC to the old cast
    - ditched the AAV idea and running a new 2" stack to roof
    - move current lav connection to the new stack since the old stack was receiving discharge from above
    - wet vent the new shower p-trap through the lav
    - new plumbing connections for the washer and the floor drains on the other side of the wall.

    Everything should work much better now. I have to tie up a couple loose ends and then I'll be ready for the inspection/testing.

    Thanks for all of your input.

  13. #13
    Plumber jimbo's Avatar
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    Nukeman...how's your tritium monitor reading lately? News today is that ground water around Connecticut Yankee has 70,000 picocuries per liter. ( Do they actually use picocuries anymore? I was reading something about becquerels??)

  14. #14
    Nuclear Engineer nukeman's Avatar
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    Can't say that I've checked. I'm not glowing yet, so it's probably okay.

    For the units, it is just like between gallons and liters. You see both units. Bq is the SI version (like liters is to gallons). Bq is the more official standard these days, but I suspect the Curie will stay around for awhile. Old habits die hard, ya know?

    http://en.wikipedia.org/wiki/Becquerel

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