Bathroom remodel DWV system

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JMC21

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Hello,
I am currently remodeling a bathroom in a small home I just purchased out in the country. I don't think they are very strict as far as plumbing code here but I would like to do things the correct way. It is in Michigan so will be based off IPC.

First picture is the current DWV set up. There is only the one bathroom group in the house and also the kitchen sink, no other plumbing fixtures in the house. I feel like they have it vented a bit odd with the 4" pipe going up through the roof and not inside of the wall framing, so that has got to go.

The second picture is the proposed new layout looking at the setup from down in the crawl space. The lav is being moved to the opposite side of the bathroom (behind me in the picture), the toilet is directly above the main stack, and the bathtub drain will be adjacent to the toilet to the left. I would like to get rid of the 4" vent and horizontal arm coming off of the main stack to the left.

The third picture is more of a side view of the whole bathroom from top to bottom. I'd basically like to get it where I can get rid of that original 4" vent coming off the horizontal pipe from the main stack. Instead I would vent it up through the dry vent coming up off the lav and meeting up to the existing 4" vent going up through the roof. Then wet vent 2" down from the lav, picking up the bathtub, and WC which is basically directly over the main stack going out to the septic tank. I don't know if the kitchen sink can stay the way it is, it is not vented any other way currently. Was thinking to just add an AAV for the kitchen sink vent.

Please let me know if this looks like it would work or what would need to be corrected. Any and all help is greatly appreciated as I am a newbie on here. Thank you.

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wwhitney

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Pretty sure that 4" cross has to go, it looks like there's no radius to the side connections, so it's not a double san-tee. I could be wrong on that, haven't see a 4" cross like that before.

Both your kitchen sink and your lav will need dry vents at the elevation of the sink trap. At least one of those has to go through the roof; the other could be an AAV or can go through the roof (individually or by joining the other one).

Then to wet vent the tub via the lav drain, the tub trap outlet has to be at the same elevation (other than the 2% slope) as the lav drain it joins. That is, the tub drain can't turn down before being vented; the vent connection (the horizontal wye joining the tub drain and the lav drain) has to be within one pipe diameter vertically of the tub trap outlet.

The WC has no such vertical limitation. If you're redoing that 4" cross, then there's something to be said for using (2) separate wyes/combos/san-tees on the vertical section, with the kitchen sink coming in below the tub/lav drain. The kitchen sink can't come in above the tub/lav drain if the tub/lav drain is to wet vent the WC; and if you use a double san-tee, that's probably OK but is definitely borderline.

Likewise, if you're ever going to add a laundry or laundry sink, it needs to join the 4" drain downstream of the lav/tub/WC. That is non-bathroom fixtures can't be part of the bathroom horizontal wet vent.

Cheers, Wayne
 

John Gayewski

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I think this is sdr35 pipe and fittings. You need to convert to sched 40. You might want to think about replacing the sdr35 underground also as it's easily crushed or ovaled and not allowed here anymore, not sure about where you are, but it's a crappy product with limited usability.
 

JMC21

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Pretty sure that 4" cross has to go, it looks like there's no radius to the side connections, so it's not a double san-tee. I could be wrong on that, haven't see a 4" cross like that before.

Both your kitchen sink and your lav will need dry vents at the elevation of the sink trap. At least one of those has to go through the roof; the other could be an AAV or can go through the roof (individually or by joining the other one).

Then to wet vent the tub via the lav drain, the tub trap outlet has to be at the same elevation (other than the 2% slope) as the lav drain it joins. That is, the tub drain can't turn down before being vented; the vent connection (the horizontal wye joining the tub drain and the lav drain) has to be within one pipe diameter vertically of the tub trap outlet.

The WC has no such vertical limitation. If you're redoing that 4" cross, then there's something to be said for using (2) separate wyes/combos/san-tees on the vertical section, with the kitchen sink coming in below the tub/lav drain. The kitchen sink can't come in above the tub/lav drain if the tub/lav drain is to wet vent the WC; and if you use a double san-tee, that's probably OK but is definitely borderline.

Likewise, if you're ever going to add a laundry or laundry sink, it needs to join the 4" drain downstream of the lav/tub/WC. That is non-bathroom fixtures can't be part of the bathroom horizontal wet vent.

Cheers, Wayne
So assuming I dry vent the lav up through the roof as planned, and get an AAV for the kitchen sink. Is it ok to do away with the existing 4” vent shown in the first picture which goes off the left side of the cross up through the floor and the roof?

Also is there a max length the 2” wet vent can be? Seems like it would be somewhere around 8-10 ft here.

Thanks.
 

wwhitney

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To tell the difference, 4" SDR35 is 4.25" OD, and 4" Schedule 40 is 4.5" OD.

Cheers, Wayne
 

wwhitney

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1) Definitely yes if the lav vent through the roof is 2". With a 4" building drain, even though it could be 3", I'm not clear if the minimum dry vent under the IPC would be half of the minimum building drain size (half of 3" = 1-1/2") or half of the actual building drain size (half of 4" = 2").

2) The length of the wet vent is not limited. Only the length of a trap arm, between the trap and the vent connection (be it dry or wet). And what a horizontal wet vent carries (only bathroom fixtures).

Cheers, Wayne
 
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