Venting plan question

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Dmt78, Oct 21, 2021.

  1. Dmt78

    Dmt78 New Member

    Joined:
    Oct 21, 2021
    Location:
    Louisiana
    My plumber backed out on us and have not been able to get any call backs from any others, so looks like we are on our own. I am trying to plan my under slab stuff so we can pour.
    The drain seems pretty straight forward, but the venting has me confused. See plumbing layout below. Note we will have two sinks in the master bath, plan shows one. Also we have a one room loft directly above both bathrooms, so hopefully can vent around that room?

    Questions:
    1. What fixtures should/can I combine to vent together? I’d like as few roof penetrations as possible.

    2. Do the toilets and tub/showers vents need to connect under slab close to the p-traps then come up a wall?

    thanks for any advice and help.
    [​IMG]
     

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  2. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Up.codes says Louisiana uses the IPC. Sounds like two stories, but no plumbing upstairs?

    If you follow the drain layout in your drawing, each fixture gets its own vent. So in terms of pipes sticking up out of the slab, each sink and the washer standpipe would have one, each WC would have two (drain and vent), and each tub would get a slab blockout, maybe extending just to the edge of the wall plate (not sure what standard practice is for tubs on slabs).

    And the right hand WC drain layout is no good, the vent can't be upstream of the toilet flange (a flat vent), so the drain should go up and to the left of the toilet flange to pass under the wall behind the toilet on its way to the building drain, with the vent takeoff under that wall.

    Once the vents are in your walls, you can combine them at an elevation that is at least 6" above the flood rim of any of the fixtures served by the combined vent. And you can run them horizontally starting at the same height, so you can jog the vents in the floor framing above to avoid rooms directly above the first floor walls with vents. If you have an attic above the second story, you could combine all the vents there for a single roof penetration.

    You could reduce the number of vent takeoffs and the number of drains going to the building drain by wet venting each bathroom. So within each bathroom, the drains would connect under the slab there, with a single branch drain to the building drain. And the bathroom would have only one vent takeoff, for the lav(s). If that interests you, I could sketch it out on top of your plan.

    Cheers, Wayne
     
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  4. Reach4

    Reach4 Well-Known Member

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    Location:
    IL
    Feeding the shower into a wye that carries the left toilet waste will wet-vent the toilet.

    Feeding the lavatory or shower drains into the right toilet waste will wet-vent the toilet.

    If you can run on another level, you could get by with even fewer vents.

    Is that area behind the left toilet a stairway to an upper level?
     
  5. wwhitney

    wwhitney Well-Known Member

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    Location:
    Berkeley, CA
    Oh, I missed the shower next to the garden tub. Looks like the shower is currently dry vented and wet venting the tub. That's the only use of wet venting in the drawing. But as Reach4 points out, you could eliminate the two WC vents pretty easily by wet venting them. And with a little more effort you could eliminate the tub and shower vents by wet venting each bathroom via its lav(s).

    Cheers, Wayne
     
  6. Dmt78

    Dmt78 New Member

    Joined:
    Oct 21, 2021
    Location:
    Louisiana
    Wow y’all have been very informative. Thanks for taking the time to detail everything.

    No plumbing upstairs. The upstairs is just one bedroom centered directly over both bathrooms. Front and back sides will be attic space.

    I’ve heard wet venting is a no-no is some codes. I can confirm with my area codes. Is it a better option to vent as drawn? I don’t mind connecting them in the wall/attic if need be.

    So the double sinks would need just one pipe coming up which will be the drain for both and vent up the wall, correct?

    Thanks for the help. Much appreciated!
     
  7. Dmt78

    Dmt78 New Member

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    Oct 21, 2021
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    Louisiana
    So the blackout boxes for tubs would just have a drain pipe up into that box and will vent from that same pipe?
     
  8. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    I know of no such code, but horizontal wet venting is only for bathroom stuff. The codes like vents that are "washed", and wet vents get easier routing rules. IPC dry vents have to be within 45 degrees of plumb, where bathroom wet vents can go "horizontal".

    https://www.iccsafe.org/wp-content/uploads/20-18927_GR_2021_Plumbing_Venting_Brochure.pdf describes IPC venting rules. See the drawing on page 12.
     
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  9. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    I think all the codes allow wet venting now. If I recall 15 years ago the UPC didn't, but I could be wrong. Some still say separate dry vents is better. I don't really know. You could still have separate dry vents while combining the bathroom fixtures into a single branch drain for each bathroom.

    You can stub up a single drain behind one of the sinks, and then put a san-tee in the wall behind each sink. One is directly over the stubbed up drain, with a vent straight up; the other would have a drain that turns horizontal below in the wall to join the stubbed up drain, and a vent above that revents to the other sink vent. I think there's some wisdom to not using 1-1/2" below the slab, so the common drain would be 2".

    This is not something I've done before, so I'm not sure I have all the details correct, but:

    You'd block out an area so the slab has a hole in it for the tub trap and connections. The tub drain would be run into the side of the blocked out area for trap installation at the time of tub installation. The blocked area would need to be big enough for the trap and the vent takeoff before connecting to the horizontal stub out.

    The vent needs to rise vertically, but that includes up to 45 degrees off plumb. So the vent takeoff could be not directly under the wall but move into the wall as it rises. That would require some void space above the slab underneath the tub, but I think that's common on most tubs. Or if the slab void (block out) extended under the wall plate, it would be easy to do a vertical vent takeoff, but I don't think that's typical.

    Cheers, Wayne
     
  10. Dmt78

    Dmt78 New Member

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    Location:
    Louisiana
    Thanks for the information. It’s been very helpful to see examples. Someone suggested the layout below to me. Seems close to the methods y’all were explaining.
    DCF89CEA-8F44-404B-B85D-9D094BBB1A1B.jpeg
     
  11. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Yes, below is how I might wet vent each bathroom under the IPC, same idea as the previous picture. A few comments:

    Purple is the 4" building drain, Red is 3", Blue is 2".

    It's important that the lav hit the 3" WC drain upstream of the shower/tub in each bathroom. That's an error in the previous drawing in the right side bathroom.

    The blue shower/tub trap arms are limited to 2" total fall, so at minimum 1/4" per foot, maximum 8' in length if you get exactly the right slope. If the trap arms in the right bathroom would be too long, you could jog the red WC drain to the right, just like in the previous drawing.

    Vents are not shown, but they would be above the lav drain in each bathroom. IPC allows 1-1/2", but 2" is fine/maybe better. The double lav would get plumbed as previously described (I could draw an elevation of the lavs if that's not clear).

    Cheers, Wayne

    05ac5aca_1982_4bfb_8867_614f99815dd1_5bc420fc55c2178960304bf35b5c559bb76fb11d.jpeg
     
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  12. Reach4

    Reach4 Well-Known Member

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    Sep 25, 2013
    Location:
    IL
    delete
     
    Last edited: Oct 22, 2021
  13. wwhitney

    wwhitney Well-Known Member

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    Location:
    Berkeley, CA
    And this is how you could do things if you want each fixture to be dry vented. Same color code as before, but the orange circles are vent stub ups, either 1-1/2" or 2". Not shown for the lavs, as it comes off from the lav-drain at the san-tee higher up in the wall. And for the tubs, it might not be a separate underslab stubup, depending on how the tub blockout works.

    This gives you a total of 8 dry vent takeoffs for the bathrooms vs the 3 in the wet venting diagram (one for each lav). But the vents are spread around in just 3 walls, so within the wall framing, at least 6" above the flood rims, the vents could go horizontal and join, giving you just 3 vents entering the floor framing above. That's just one more location than in the wet venting version (where the two double lav vents combine in the wall), the extra dry vent is over by the garden tub/shower.

    Cheers, Wayne


    05ac5aca_1982_4bfb_8867_614f99815dd1_5bc420fc55c2178960304bf35b5c559bb76fb11d (1).jpeg
     
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  14. Dmt78

    Dmt78 New Member

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    Location:
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    Thanks Wayne, that’s very helpful and vents seem simpler than the original layout. Much easier to understand seeing it. Greatly appreciated sir!
     
  15. Dmt78

    Dmt78 New Member

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    Oct 21, 2021
    Location:
    Louisiana
    Maybe someone can offer some advice on this situation. First photo is the bathroom on the left. Second photo is the master bathroom on the right of the plans.
    I was dreading the pipe ending right in the middle of a footing, but it appears the tub/shower drain will.(the small orange dot at the bottom of the footing on the left of the first photo. )
    I know I have to sleeve the pipe with 6" pvc if running horizontal through footing, and foam wrap/tape going vertical.
    Any experience with this situation and what's my best course of action? Also, does the layout look correct so far?

    Thanks for any advice.
     

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  16. John Gayewski

    John Gayewski In the Trades

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    Aug 7, 2021
    Location:
    Iowa
    I only skimmed three above comments but,

    You don't have to be so deep with the laterals if you vent individually. You can run the main deep like you have it and come up out with a wye and 45. Then drain and vent much shallower (if that's a word). Also toy can have shorter ditches as you just need to 90 over to where your going vs. digging longer 45 degree ditches. This will also help you get up out of the footings.
     
  17. Dmt78

    Dmt78 New Member

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    Oct 21, 2021
    Location:
    Louisiana
    Thanks John. I was concerned with keeping only the 1/4” drop to the main drain line, so I was digging down so I could meet the main at that slope. Could I just drop down greater once I get to the main 4” pipe? Also, can my tub, toilet, and sinks drain at a lesser angle towards the 3” branch (connect via 3-3-2 wye with long 45?)
     
  18. John Gayewski

    John Gayewski In the Trades

    Joined:
    Aug 7, 2021
    Location:
    Iowa
    Yes short runs of vertical piping are common. 1/4" slope to a drop, then down into the main. .
     
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  19. Dmt78

    Dmt78 New Member

    Joined:
    Oct 21, 2021
    Location:
    Louisiana
    Would this option be better? Drain and vent tub separately? Only issue is it may connect to main drain really close to washer drain up top. Suggestions? Sorry for all the questions, just want to get this right. Thank you.
     

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