Wet vent without the dry vented fixture

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by ghaun, Mar 12, 2021.

  1. ghaun

    ghaun Member

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    West Chester, PA
    So this may seem like a crazy question, but I have a scenario where having a vent up-stream a few feet for my tub would be preferred, as I have a wall there that I could come up. So my question is as such, if there was a vanity there, I could connect to that and use as a wet vent. So imagine as if the vanity was not there, why can't this serve as a vent. The pipe would be horizontal for a few feet up-stream and then continue vertical in the wall.

    If I am missing something very common sense, then excuse my ignorance.

    Thank you for the help.
     
  2. Reach4

    Reach4 Well-Known Member

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    You mean the vent would be a few feet downstream of the tub trap, I think. Water flows downstream.

    You might try a sketch, but there is a good chance that what you are asking is doable.

    Edit: IPC does not allow horizontal dry vents.
     
    Last edited: Mar 13, 2021
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  4. Jeff H Young

    Jeff H Young In the Trades

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    because code doesn't allow it. dry vents rise 6 inches above flood level before going horizontal or connecting with another. to keep vent from plugging up would be one reason for this
     
  5. ghaun

    ghaun Member

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    As an example, in the picture that I have attached, imagine as if the vanity was never connected to the vertical. It would just be a vertical vent pipe. Why is a wet vent allowed, which actually has water running down that pipe? ...but by removing the vanity and not having water, that vent would not be appropriate for the shower or WC. ...or is it? My specific scenario would be removing the BT and WC from the picture and replacing the shower with a BT. The vent would be upstream and be flat before rising vertical.
     

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  6. Reach4

    Reach4 Well-Known Member

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    The thought is that the lavatory flow will help keep the piping clearer.
     
  7. Jeff H Young

    Jeff H Young In the Trades

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    ghaun there is a right way and wrong way . your way is wrong re read posts kinda hard to more fully explain
     
  8. ghaun

    ghaun Member

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    Jeff H. Young, I know that it is wrong. I was only asking from a physics and engineering standpoint as to what is different. That is all!

    I thought about the flow to keep it clean. That was all that I could think of, which does make sense.
    Reach4, thank you for confirming that!

    So as long as I can get some fixture behind this like a lavatory to flush the junction between the flat vent created by a horizontal vent, then I am good. Unfortunately, I cannot.

    So, the only thing that I can come up with is the attached picture for my application. The top would be a vent and the bottom long turn would bring me back inside the joist cavity when runs back to the main branch. This is a 180, which I don't know if this introduces any issues with regard to cleanouts, etc. The only other option is to use a 3" trap/arm and run within a soffit perpendicular to the joists and under them in order to have a vent run to the next wall. I would rather go with the attached picture.

    Thoughts?
     

    Attached Files:

  9. Reach4

    Reach4 Well-Known Member

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    Should be good if that trap is for a tub or shower, which will then go on to wet-vent a toilet.

    The toilet has its own trap, so if this is a toilet only idea, you would replace that trap with a a 4x3 closet bend or 3 inch medium bend instead of the trap.
     
  10. ghaun

    ghaun Member

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    One other comment, my tub will be direct drain, so the normal arm off the drain to the overflow will not be a part of the normal drain pattern, it will only be utilized in the case of overflow. The picture that I had attached above is not much different than the overflow path typically taken. I just wanted to point out that the top of the trap will connect directly below the tub drain, of course with the 't' above it for the overflow.
     
  11. Jeff H Young

    Jeff H Young In the Trades

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    pic in post 7 is a good way of venting
     
  12. ghaun

    ghaun Member

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    Reach4, thank you! This is for a free-standing tub. This drain will only serve the tub and connect back to the main branch. I will be putting an AAV behind the tub out of the floor, which will rarely be seen because of the large tub next to a window. I don't want a vent in the outside wall, let alone the window in the way. I have gone to great lengths on the rest of this project, but this is a difficult one. The joists run perpendicular to the window and the tub drain would run from the tub toward the middle of the house, where it would dump into a slightly lower main branch running perpendicular to the joists. I would rather use an AAV over punching a hole through the joists.
     

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    • Tub.jpg
      Tub.jpg
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  13. Jeff H Young

    Jeff H Young In the Trades

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    Ghaun, maybe like your pic in post number 7 AAV on top if allowed in your jurisdiction. that's a perfect way of venting (other than the AAV) but if legal a good second choice. under a window and coming up a wall and through roof not what you like to do understandable
     
  14. ghaun

    ghaun Member

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    Jeff and Reach4, thank you.

    Unfortunately, I just realized that the above option won't work because of joist depth. I do have a few other options which might work. I do have a soffit below this area perpendicular to the joists, so the trap can hang down, but not the run of pipe in the joist cavity.

    Unfortunately, both options involve an AAV.

    Option 1, would involve 135 degrees of horizontal turn (I am assuming that the 45 degree angle gained out of the trap does not count) with a tee on its back at a 45(I know, but this is a vent and will never be used as a drain in the future, as it is for an AAV in the floor) so that I can clear the back of the tub and bring the AAV up above the floor. The AAV would be hidden from view by the tub against the window.

    Option 2, would involve an AAV inline on the trap arm coming to the main horizontal drain. I do have clearance and could have a vent in the ceiling for air admission.

    I would love to get your thoughts. Again, I just don't have a way to regularly vent this area, given the low window and no nearby walls.

    Thank you!
     

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  15. Jeff H Young

    Jeff H Young In the Trades

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    I think your code allows santee on back mine would require a combi but other wise good. not sure on your clean out requirements but if the 4 inch main (or 3inch hard to tell) has c/o I think you can service tub drain well enough
     
  16. Reach4

    Reach4 Well-Known Member

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    6 ft IPC max for 1-1/2-inch trap and trap arm
    8 ft IPC max for 2-inch trap and trap arm

    AAV must be accessible and must be in area that admits air.
     
  17. ghaun

    ghaun Member

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    All, thank you for your help. I am working through some other ideas. I have a vanity past the tub that I could use as a wet vent. In doing this, the vanity sink trap arm becomes 8', over the limit for 1.5". I could upsize to 2", but then I would be pushing the limit for going through multiple studs.

    I know that the original reason for not having a vent extending past the fixture was keeping it washed. I have attached a diagram which uses the concept of a wet-vent for the tub using the vanity sink, with an extra vent on the vanity sink trap arm (relief-vent ?). Is this even such a thing or allowed.

    You can also see in my picture where I have the drain for the tub extending 12' to another vent down-stream. I have this pipe in 3", but this too was pushing it. The yellow shows the two areas for possible venting.
     

    Attached Files:

  18. wwhitney

    wwhitney Well-Known Member

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    I don't follow your picture--needs more labeling and a key for the color coding.

    I don't see why there would be a relationship between the sink trap arm length and whether you use it for wet venting the tub. You can pull your sink dry vent off the 1.5" trap arm anywhere within the first 6' of length, with the drain continuing on horizontal (use an upright combo for the takeoff) or turning vertical (use a san-tee as usual). Then you just bring your sink drain over to combine horizontally with the tub trap arm, meeting the tub trap arm within 6' of the tub trap if it is 1.5", or 8' of the tub trap if it is 2". The IPC would allow you do do the tub and sink all in 1.5", including the wet venting, but arguably 2" is preferable for the tub.

    Cheers, Wayne
     
  19. ghaun

    ghaun Member

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    Wayne, sorry on the drawing. I have added some comments. I thought that the dry vent for a wet vent had to extend vertical without any jogs. ...but are you saying that I can have a single dry vent in the middle of the two that I have drawn for the sink and still accomplish a wet vent for the tub? Also, the wet vent portion that I had drawn has to be there as there is a soffit below. The joists run perpendicular.
     

    Attached Files:

  20. ghaun

    ghaun Member

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    Btw, ignore the color for now. These were my temporary additions. Sorry.

    My only other option for venting the tub was using the 3" drain for the tub and then venting off the other "yellow" dry vent at the end that I had drawn which is 12' away. That was a vent for my shower, which would become a common vent.
     
  21. wwhitney

    wwhitney Well-Known Member

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    Location:
    Berkeley, CA
    Dry vents need to be "vertical" from their takeoff to 6" above the flood rim level of the fixture served. Likewise when you connect dry vents, the connection needs to be 6" above the flood rim level of any of the fixtures being dry vented.

    You can do something like the drawing below. I didn't follow what you said about the soffit, but I'm assuming you want the sink drain to stay horizontal until that point you had it turn down.

    Sizing for the IPC would be: 1-1/2" for dry vent and sink drain/wet vent up to tub; 2" for combined sink/tub drain/wet vent up to WC; 3" for WC and downstream.

    Cheers, Wayne

    Bathtub Markup.jpg
     
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