Wet vent configuration / distance from toilet flange

[SteveIA]

What are limitations / best practice guidance on how close to a toilet a wet vent needs to tie into the 3" drain pipe?

I'm wanting to tie a 2" wet vent into 3" horizontal about 5' downstream of the toilet (via a 3x3x2 wye rolled up maybe 20 degrees--so wet vent line comes in real close to top of 3" pipe)
The 2" wet vent would run horizontal about 3', then turn straight up and continue through roof. (Catching a shower on the horizontal and single lav into the vertical)

What I'm finding indicates vent should be within 6' of trap for 3" pipe, but that seems to be in reference to a dry vent... not sure if wet vent is handled differently, or if I need to account for the 2" horizontal run separately?

I'm doing a minor bathroom remodel in a rural area (not subject to inspection) but trying to do things right. I would have liked to hire a plumber and not mess with it myself, but getting someone to show up / return a call has been problematic so I eventually gave up and started trying to learn enough to just DIY so I can move on with the rest of the project. Thought I had everything figured out, but had someone who should know what they're talking about look things over before gluing anything and they thought I needed to add another vent closer to the toilet. I have a wall on the "far" side of the toilet I can run a vent up through, however being an old house with undersized joists means limited height (and 3" obviously needs to be where it needs to be to get proper slope)... so getting a vent tied in and turned the direction it needs to be seems like it might be tricky. So I'm trying to understand the "why" before I mess with adding/changing things.

My thinking is that one 1.6g toilet should never fill the the 3" more than half full, and if the 2" ties in within the 6' distance on the top half of the pipe it seems like I should be fine with what I have? I would not think the shower/lav should ever come close to filling the 2" to cause much air restriction, or significantly add to the fill height of the 3" pipe. Am I missing something?

It looks like Iowa uses UPC if that matters.

I'll try to add a diagram and/or pictures in case that helps explain configuration/geometry better, but it will probably be later this evening before I have a chance to draw something.

 

[Reach4]

Your plan of wet venting the toilet with the shower sounds right.

It looks like Iowa uses UPC if that matters.

6 ft under upc.

Unlike trap arms for most stuff, the toilet trap arm does not need to stay horizontal before being vented.

 

[Sponsor]

 

[wwhitney]

(via a 3x3x2 wye rolled up maybe 20 degrees--so wet vent line comes in real close to top of 3" pipe)

I would think "rolled up" means relative to horizontal, so 20 degrees wouldn't put the side connection very close to the top, compared to rolled up 90 degrees. Anyway, for horizontal wet venting, there's no need to roll it up (beyond for the 1/4" per foot slope coming in), although I would think it would be OK to roll it up 20 degrees.

BTW, for toilets under the UPC, the 6' distance limit is measured along the pipe starting at the closet flange. Presumably since there is no external trap.

Cheers, Wayne

 

[SteveIA]

I would think "rolled up" means relative to horizontal, so 20 degrees wouldn't put the side connection very close to the top, compared to rolled up 90 degrees.

Correct. My understanding is for a horizontal wet vent, you want wyes at 45 or less above horizontal. I'm not saying the 2" goes into the top of the pipe, but being rolled up, the top edge of the 2" hole inside the wye is not significantly down from the top of the 3" pipe. (So say *if* the 3" line were 90% full, it could still pull air through the wet vent.)

In this case the exact angle of roll was sort of predicated by where I needed things to come out to get the 2" line to land in the center of the joists, so I could drill 2.5" holes without significantly weakening things.