Lavatory absolutely need a dry vent above?

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Hello all, my laundry is complete and demo begins on 4 other rooms next weekend. One of my tasks coming up will be to figure out the DWV routing for a dual bathroom group. The existing conditions include a single 2" vent pipe through the roof and a 3" drain line that I will be draining to. Everything in between is getting ripped out. I know I will be doing a horizontal wet vent system and that each fixture drain needs to connect individually. I am on Florida's version of IPC.

My question is about a lavatory. Every picture I have ever seen had a vent pipe directly connected above the fixture drain for the lav. My problem is that where this is to be installed is directly under a window on a masonry wall and the sink cabinet is flanked by drawer cabinets on both sides. This means unless I change something (which if I have to I have to and will figure out) I need to go down. The existing vent is on the wall beside one of the flanking drawer cabinets.

What I am envisioning is that the 2" vent pipe would go from roof penetration straight down through wall and floor and then bend toward the eventual 3"drain. The lav fixture drain (after the trap) would go to the wall behind the sink and then 90 bend down through the floor, bend again towards the vent pipe and connect to the horizontal pipe thus creating the beginning of the wet vent. My understanding for IPC is that I have 5' developed length to make that happen. The next connection would be the toilet so it upsizes to 3" from there on.

I can't find a picture representing this sort of setup so I am asking if this is allowed.

1662384201095.png


please excuse the crude paint sketch. I have CAD drawings at work that I will create some images to go with this tomorrow but I wanted to get the ball rolling today. Thanks in advance for any knowledge shared.
 

wwhitney

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Every external trap needs a vent connection at the elevation of the trap. More precisely, before the drain has fallen more than one pipe diameter from the trap outlet. This prevents siphoning of the trap.

So your drawing definitely doesn't work, as you have the drain turn down before it's vented. If you are under the IPC, then with a 1-1/2" lav trap, your lav drain could travel as far as 6' horizontally (including the portion outside the wall) at a perfect 1/4" per foot slope before you hit the 1-1/2" fall limit. So perhaps that is enough to get out from under the window.

The other option the IPC allows is to use an AAV, which can be in the cabinet under the lav.

Cheers, Wayne
 

John Gayewski

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I think i would have a faux drawer on one of these cabinets or something like that to run a vent pipe.
 
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Every external trap needs a vent connection at the elevation of the trap. More precisely, before the drain has fallen more than one pipe diameter from the trap outlet. This prevents siphoning of the trap.

So your drawing definitely doesn't work, as you have the drain turn down before it's vented. If you are under the IPC, then with a 1-1/2" lav trap, your lav drain could travel as far as 6' horizontally (including the portion outside the wall) at a perfect 1/4" per foot slope before you hit the 1-1/2" fall limit. So perhaps that is enough to get out from under the window.

The other option the IPC allows is to use an AAV, which can be in the cabinet under the lav.

Cheers, Wayne
Right. I figured there was a reason I had not seen it that way lol.
So, yes I can do 5' on the 1-1/4" 6' on 1-1/2". Getting out from under the window wasn't really the problem. The wall the window is in is masonry and structural. I had not planed to build out a wood wall there due to limited space for the cabinet. The vent pipe is to the side anyway so going out to the side would be better but I have drawers (which as John said above I could fake a drawer front).
There are definitely options, I just was hoping I could go down.

I will look further into the AAV...I have not used one or really understood them but I did see it mentioned in the code.
 

Reach4

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AAV at least 4 inches above the trap arm. There are more precise descriptions available, and the required height might be lower than you would first think.
Must be accessible to change it out. Reach under the vanity maybe, but they make boxes with louvered covers to let you build them into a wall.
Must have enough ventilation, but under a bathroom vanity is enough ventilation.
 

wwhitney

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Yeah, I don't have a wood wall there to plumb in. Adding one would make cabinet encroach the doorway.
With a wall, you could make the vanity less deep. Or without a wall, you could shorten one or more of the drawers.

Cheers, Wayne
 
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Reach4

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Yeah, I don't have a wood wall there to plumb in. Adding one would make cabinet encroach the doorway.
How about a photo of what you do have. Include the vent from above, the drain line you want to dump into and where you would like to put the trap adapter. 800 pixels and 200 KB max.

If the cabinet will cover that area, I suspect you could modify the cabinet to clear, but hide, a pipe that is outside of the brick wall.

If not, that AAV works.
 
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How about a photo of what you do have. Include the vent from above, the drain line you want to dump into and where you would like to put the trap adapter. 800 pixels and 200 KB max.

If the cabinet will cover that area, I suspect you could modify the cabinet to clear, but hide, a pipe that is outside of the brick wall.

If not, that AAV works.
Sorry Reach4...the room has not been through demo yet, my dumpster shows up Wed. Picture of room would be useless.
This (below) is a snip from the plans showing the two bathrooms that might help. The vent is somewhere in the green area. Pink is the 3" I am tying into. Yellow is the sink in question. Second pic is the existing floor plan.

Yes cabinet modification is always an option. There might even be room behind the drawers, I have not built one of them yet.

1662403098832.png

1662403152156.png
 

Jeff H Young

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an AAV is basicaly a one way or check valve it allows air in so pipes can drain without siphoning out the p trap but wont allow stinky to enter your home . often used in a bind like you apperar to be in. my opinion its not the same or equivilant to a real vent but in practical use should work without any problem
 
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How about a photo of what you do have. Include the vent from above, the drain line you want to dump into and where you would like to put the trap adapter. 800 pixels and 200 KB max.

If the cabinet will cover that area, I suspect you could modify the cabinet to clear, but hide, a pipe that is outside of the brick wall.

If not, that AAV works.
See anything jumping out at you as being a bad idea on this? I think I have conceded that I will lose a drawer to make this work.

1662483587913.png
 

wwhitney

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Comments, based on yellow horizontals being above the floor, and tan horizontals being below the floor:

- 90" is too long for a 1.5" trap arm (upper shower). But a shower is better served by a 2" trap, and a 2" trap arm can be 96" if you achieve a perfect 1/4" per foot slope. Close enough to the limit that I might try to shorten the trap arm further.

- The lav trap arms can be 60" long with a 1-1/4" trap or 72" long with a 1-1/2" trap, but still seem unnecessarily long to me. I'd be inclined to have separate san-tees for each lav, with each san-tee closer to the lav itself, and then take those 2 vent takeoffs and recombine them with the existing vent with the walls, at least 6" above the lav flood rims.

- If you post the floor plan without the drain overlay and text boxes, I could draw a suggestion.

Cheers, Wayne
 
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Comments, based on yellow horizontals being above the floor, and tan horizontals being below the floor:

- 90" is too long for a 1.5" trap arm (upper shower). But a shower is better served by a 2" trap, and a 2" trap arm can be 96" if you achieve a perfect 1/4" per foot slope. Close enough to the limit that I might try to shorten the trap arm further.

- The lav trap arms can be 60" long with a 1-1/4" trap or 72" long with a 1-1/2" trap, but still seem unnecessarily long to me. I'd be inclined to have separate san-tees for each lav, with each san-tee closer to the lav itself, and then take those 2 vent takeoffs and recombine them with the existing vent with the walls, at least 6" above the lav flood rims.

- If you post the floor plan without the drain overlay and text boxes, I could draw a suggestion.

Cheers, Wayne
Oppps, yeah that shower drain was supposed to be 2" which I read in IPC would go 8'
My sources have me at 5' for 1.25 trap and 6' for 2" trap...where are you getting 60" and 72".
I completely forgot about the ability to vent the sinks separately and combine vents above, I will put some thought into that.
The floor plan image is a couple posts above this...
 

wwhitney

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An option for your consideration. It keeps the two bathrooms separate, although that is not required by the IPC.

Red is 3", Blue is 2", Green is 1.5". Green circles are the lav dry vent takeoffs; green between lav and circle is above the floor; the rest is below the floor. Tub and shower show explicit u-bend (not to scale), and tub is in 2" just because. [If you switch to 1.5" for the tub trap, then if you bring the lower lav to the tub as shown, you'd still need 2" after the tub/lav junction. Or you could just continue the lav straight across to the 3" WC line.]

Cheers, Wayne

1662403098832.png
 
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An option for your consideration. It keeps the two bathrooms separate, although that is not required by the IPC.

Red is 3", Blue is 2", Green is 1.5". Green circles are the lav dry vent takeoffs; green between lav and circle is above the floor; the rest is below the floor. Tub and shower show explicit u-bend (not to scale), and tub is in 2" just because. [If you switch to 1.5" for the tub trap, then if you bring the lower lav to the tub as shown, you'd still need 2" after the tub/lav junction. Or you could just continue the lav straight across to the 3" WC line.]

Cheers, Wayne
Thanks for that. I will definitely consider it. I am sure there are a dozen ways to lay it out...I was more concerned with if I had the concept correct, which based on what you drew seems like I did. Not sure I understand the explicit u-bend reference. Both of those would get traps under them right?
 

wwhitney

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Not sure I understand the explicit u-bend reference.
I just mean I'm showing that the trap outlet doesn't correspond to exactly under the drain, because of the u-bend of the trap. That's why I drew little short segments at the drain of the bathtub and shower. The u-bend gives you a small offset for free, because you can swivel the u-bend / outlet elbow joint however you like. The 90 I drew is just the trap outlet elbow.

[Also, on the top of my drawing, it looks like the lav and shower could be joining at a double wye. Those are to be avoided on the horizontal because they are a "flat" fitting, and two single wyes in succession is better. I'm trying to show the WC/lav wye upstream of the shower wye, as is required for wet venting.]

Cheers, Wayne
 
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I just mean I'm showing that the trap outlet doesn't correspond to exactly under the drain, because of the u-bend of the trap. That's why I drew little short segments at the drain of the bathtub and shower. The u-bend gives you a small offset for free, because you can swivel the u-bend / outlet elbow joint however you like. The 90 I drew is just the trap outlet elbow.

[Also, on the top of my drawing, it looks like the lav and shower could be joining at a double wye. Those are to be avoided on the horizontal because they are a "flat" fitting, and two single wyes in succession is better. I'm trying to show the WC/lav wye upstream of the shower wye, as is required for wet venting.]

Cheers, Wayne
Got it...makes sense. And yeah I knew to avoid the flat double. both sides need to come in above the centerline and individually.
Thanks a lot Wayne. Plenty to think about.
 
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