Wet vent bathroom group?

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DaveNewhampshire

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Greetings everyone ... a few months back I posted questions on how to properly vent my bathroom I am putting in. There was a lot of great info from different people, including Wayne, but I did not want to tag off that post to avoid confusion, so I am starting a new thread with a specific question.

For background info, I am putting in a bathroom group consisting of a double lav, toilet, free standing bathtub, and stand up shower (see attached layout pic). I am in NH, and the IPC is the governing rules. The challenges I am up against are that the area below the bathroom is garage space, so I would prefer to have all plumbing be inside the wooden I-joists. The joists are 16" deep, but to maintain slope, I really only have 5 1/2 inches of drop from bottom of the subfloor to the point of entry into the main house where it will go to the basement and tie into the main septic pipe. The other challenge is that there is no good vertical wall in the direction of flow to dry vent the appliances, and IPC does not allow horizontal dry vent below the flood rim of the appliance.

What I would like to do is wet vent the whole bathroom group via the double lav 2" drain. The 2 lav drains will meet in a vertical double cross, and the 2" dry vent will extend up into the attic part of the garage and out the roof. Since I live in a cold region, I will increase the dry vent from 2 to 3 inches in the climate controlled part of the house before going up to the attic/roof. The bottom of the cross will serve as lav drains and wet vent for the toilet, shower, and bathtub. See attached diagram, and the purple colored pipes are the wet vent.

Please feel free to comment on whether this meets Ch. 9 of the IPC, as this is the simplest and straight forward solution in my (non-pro) opinion. If it won't work, then I may have to go back to other solutions, such as directing pipes to a vertical wall, even if it means going in the opposite direction or through floor joists and back again. If any part of the wet vent piping needs to be upsized to 3", I am open to that as well. Thank you in advance.
 

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wwhitney

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I'm pretty sure we covered all of this in the other thread. You've go two problems with your layout above:

1) The distance and drop from a trap (shower, tub, lav) to its vent (wet or dry) is limited based on one pipe diameter fall, which give a maximum length of 8' for a 2" trap at a perfect 1/4" per foot fall. The only vent connection you have for the WC, shower and tub is that wye in the lower left where the lav drain comes in to wet vent everything. Way too far from the tub and shower traps.

2) More basically, with wet venting, every fixture needs to be vented as it joins another drain. So the lav can wet vent everything if it is one of the two upstream most fixtures. I.e. you'd have to have the following order of connection going downstream:

2" double lav drain -- fixture 1 joins in -- fixture 2 joins in -- fixture 3 joins in.

The order of the fixtures don't matter, just that they join the double lav drain one at a time. And if fixture 3 is the WC, then the pipe between fixture 2 and fixture 3 needs to be 3".

Cheers, Wayne
 

wwhitney

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Now, the above layout would work if you dry vent the tub. E.g. you could pull a dry vent into that diagonal wall by the tub. That could be an AAV in an accessible wall box with a grill if you can't get a vent through the roof from that diagonal wall.

Cheers, Wayne
 

DaveNewhampshire

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Now, the above layout would work if you dry vent the tub. E.g. you could pull a dry vent into that diagonal wall by the tub. That could be an AAV in an accessible wall box with a grill if you can't get a vent through the roof from that diagonal wall.

Cheers, Wayne
Thanks for the reply Wayne. I did not think I asked about wet venting the whole bathroom through the lav last thread, but maybe I did ... it had more than a few side bars.

I did not take into consideration that the dry vent part of the wet vent system had to be upstream. I thought I was ok with the trap arm distance for the tub because I made the assumption that the 2" pipe coming from the tub trap was the start of the wet vent (even with water draining at the same time, the air from the lav dry vent could make it back to the tub). Now I think I understand the wet vent concept better. My flow was bathtub as the most upstream, then shower joins it, then toilet, then finally Lav. I can understand now that the tub drain would not flow well or siphoning out the tub trap because vent being so far away.

So what I hear is I need to dry vent the tub somehow, and that could be the start of the wet vent, being the furthest upstream appliance. The only problem is, although the tub and shower traps are in the same joist bay, I would either need to either go back to the diagonal stub wall, which would involve doing a 180 change in direction, or go into the next joist bay, catch the corner of the stub wall, and back through the joist and on from there. See pictures of both situations. Let me know if either would work and which would be preferable. Once in the stub wall, I would be able to get the vent pipe up to the attic area to join the lav vent and out the roof.

Thanks again for all the help.
 

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wwhitney

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Scenario 8 works and clearly involves fewer changes of direction, so that's better.

You have the option to use a 1-1/2" tub trap and then a 2 x 1-1/2 x 1-1/2 wye or combo (with the barrel horizontal) for the vent takeoff. I.e. the tub drain after the dry vent has to be 2" because it's a wet vent carrying more than 1 DFU. But you could also use a 2" tub trap and then a 2x2x1-1/2 vent takeoff.

As long as your showerhead(s) add up to less than 5.7 gpm, the shower counts as 2 DFU, and the combined tub drain/ shower drain / wet vent for the WC is only carrying 4 DFU and can be 2".

Cheers, Wayne
 

DaveNewhampshire

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I think you are correct… #8 is more straight forward as far as changes in direction. The only concern is I would lose about an inch and 1/2 of slope because I have to go through the I-joist below the flange, but I think I will have just enough slope to make it work.
I was thinking of using a 2x1.5x1.5 wye with a street 90 degree 1.5 for the vertical dry vent, and the 2 inch branch of the wye for the wet vent downstream. See picture … I only had a 2x2x2 to use as a prop but hopefully you get the idea. Thanks!
 

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wwhitney

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That's not going to work, it has a short horizontal dry vent segment between the 90 and the wye, and that is prohibited. The dry vent has to come off the upper half of the pipe. E.g. with a wye or combo with the side inlet vertical (or rolled up to 45 degrees off upright).

What's the tub model, and where exactly in your picture is the flange of the I-joist in the way?

Cheers, Wayne
 

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Thanks Wayne and Jeff ... I see that now. I need to stay as close to the top of the subfloor as possible so I was trying to go vertical in the dead space triangle area of the stub wall to buy me some vertical room in the joist bay.
The tub is BainUltra claw foot (see pic), and the space between the tub trap and the wye is where the joist flange is. Would this mock up picture work if I can make it happen using a wye and 90 street? I would use a 1.5x1.5x2 wye or reduce the 90 inlet to the wye. If I had to, I could adjust the stubwall a little or box in the vertical part of the vent as it is just the area behind the tub and not a very noticeable area. To complicate things a little more, there is a joist directly below and parallel to the wall to the right in the pic. Thanks again for the great advice!
 

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wwhitney

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The vent takeoff geometry you show is fine.

Seems like with a claw foot tub that has the waste and overflow above the floor, you don't have to have the combined waste and overflow enter the floor system directly underneath the overflow elbow. You could keep the outlet of the waste and over flow tee horizontal instead of vertical and then travel above the floor a little to enter the floor system at a convenient place with a 90. Then it should be possible to fit the trap and vent takeoff all within one joist bay, I think.

That is, if it's important that you not waste that initial 1.5" of height by having the trap outlet below the I-joist flange. Not sure how much height it will save you--if the trap outlet is tight to the subfloor, then the wye for the vent take off would stick through the subfloor.

BTW, the IPC would allow a san-tee on its back for the vent takeoff, and your situation is one in which the more compact shape that provides could make that a worthwhile tradeoff.

Cheers, Wayne
 

DaveNewhampshire

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Wayne, I was thinking of something similar, where I would keep the outlet of the trap above the subfloor, have the wye and vent above as well, and then drop the 2" drain/wet vent down into the subfloor with a couple 45's offset and then continue on from there. I would have to cut out a rectangle in the subfloor for the trap to recede into, but I would avoid cutting a hole in the web of the joist and avoiding the wasted height of having to be below the flange. Essentially what you see in the picture except the wye is flush against the subfloor.

I had not thought of your idea though, essentially is would be a "horizontal tailpiece", correct? I know there is the 24" maximum for a vertical tailpiece, but not sure if that applies to a horizontal run as well? If so, that is not a problem as I would be well within that. Then I could put the trap and wye in the joist bay and still not loose much height for sloping. In either case, I am not much concerned with the way it looks as I can box it in, or just leave it because the tub will cover most of it unless someone is laying on the floor looking under the tub or looking behind the tub itself.

I am going to go out and buy some fittings, including the san-tee, to see how it will work with a mock up. Thanks for all the help, and I think I am on my way to a final plan!
 

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The vent takeoff geometry you show is fine.

Seems like with a claw foot tub that has the waste and overflow above the floor, you don't have to have the combined waste and overflow enter the floor system directly underneath the overflow elbow. You could keep the outlet of the waste and over flow tee horizontal instead of vertical and then travel above the floor a little to enter the floor system at a convenient place with a 90. Then it should be possible to fit the trap and vent takeoff all within one joist bay, I think.

That is, if it's important that you not waste that initial 1.5" of height by having the trap outlet below the I-joist flange. Not sure how much height it will save you--if the trap outlet is tight to the subfloor, then the wye for the vent take off would stick through the subfloor.

BTW, the IPC would allow a san-tee on its back for the vent takeoff, and your situation is one in which the more compact shape that provides could make that a worthwhile tradeoff.

Cheers, Wayne
Wayne ... when you said I could keep the outlet of the tub waste and over flow tee horizontal, did you mean I should fabricate my own, or try to use the one that came with the tub? I don't see how I could turn the existing outlet of the tee horizontal and still stay above the subfloor.

To customize one, I was thinking of using the drain and overflow tailpieces into slip fittings, and then a 1 1/2 wye to go horizontal until I get it to the trap in the next bay. Let me know if I am on the right track and it's allowed per IPC. The trap should be no more than 16 inches or so horizontally from the wye. See pictures.

Thanks again!
 

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wwhitney

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Wayne ... when you said I could keep the outlet of the tub waste and over flow tee horizontal, did you mean I should fabricate my own, or try to use the one that came with the tub?
Not sure on that tubular style whether it is OK to turn the tee horizontal or not, maybe someone else can comment. They do have special side outlet tubular waste and overflows, e.g .


But I don't think you particularly need the side outlet, right? Not sure if there's an equivalent straight horizontal outlet tubular [or if you can turn the tee horizonal, then they wouldn't have a separate product for that.]

Anyway, I was mostly thinking in terms of the glue joint waste and overflows that use regular DWV fittings. Then you could just use a combo or possibly a san-tee on its back. E.g.


If your waste and overflow won't be accessible, then you need to use glue joint. If it will be accessible, then you have your choice, and of course if it will be exposed, the brass tubular looks better.

Cheers, Wayne
 

DaveNewhampshire

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Not sure on that tubular style whether it is OK to turn the tee horizontal or not, maybe someone else can comment. They do have special side outlet tubular waste and overflows, e.g .


But I don't think you particularly need the side outlet, right? Not sure if there's an equivalent straight horizontal outlet tubular [or if you can turn the tee horizonal, then they wouldn't have a separate product for that.]

Anyway, I was mostly thinking in terms of the glue joint waste and overflows that use regular DWV fittings. Then you could just use a combo or possibly a san-tee on its back. E.g.


If your waste and overflow won't be accessible, then you need to use glue joint. If it will be accessible, then you have your choice, and of course if it will be exposed, the brass tubular looks better.

Cheers, Wayne
So I hope to have the final layout. See pictures and please comment. Nice thing is the sani-tee on it's back is snug up against the bottom of the subfloor so I have plenty of room for slope as it heads to the shower and beyond. Also, I had the room so I thought I might sneak a clean out in the horizontal run from the tub outlet and the drop to the trap, so let me know if that is a good idea or not (and allowed per IPC). I plan to be able to access that stub wall as the air pump for the jets will be in there.

Now I may get the PVC drain and overflow kit you mentioned before, but I was also thinking it would be nice to be able to quickly unhook the drain/overflow and move the tub if need be. Is there an issue with mixing steel tubes with a PVC slip joint/compression adapter? Or are they only meant for PVC pipe? It will be accessible above the subfloor. Thanks!
 

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Jeff H Young

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I'd rather have a soffit in the garage than these exposed pipes in master (personal choice) . Can't that line going to the tub roll a combi for the vent toward the wall on right?
 

DaveNewhampshire

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I'd rather have a soffit in the garage than these exposed pipes in master (personal choice) . Can't that line going to the tub roll a combi for the vent toward the wall on right?
After further review, I think this is a better way to put in a clean out ... see pics.

As far as aesthetics, most of it will be enclosed in that triangle stub wall that runs parallel and right behind the tub (only the sole plate is installed now). The only exposed pipes will be the few inches of horizontal drain run, and of course the drain/overflow, but again it will all be behind the tub. See view of tub in place, and right behind it will be a stub wall that will house plumbing and the air pump for the whirlpool.

I am not sure where I could roll a combi, but does not the vent have to come downstream of the trap? So the vent needs to come from the joist below I believe. Thanks
 

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Jeff H Young

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I'm not sure exact location of joist but rolling a wye or combi up and perhaps slight notch at top of joist?
If you can make it work and upon review I think you can. I see its a precise rough in but doable.
 
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