Basement venting

getting ready to saw my basement slab to add a bath. i'm re-routing an existing vented 3" line from a first floor bath to go under the basement slab and tie into an existing under-floor vented 4" c.i. to street. i'll tie into the 3" line from the new toilet, tub & shower (all less than 5') and 1-1/2" from lav will run into the 2" shower line with AAV under the countertop. am i ok on venting depending on both the 4" c.i. line and the existing 3" as a wet vent ? thank you. al p.s. sketch at.....
Wisconsin Plumbing Code Link

The 3" and the 4" appear to be the "main drains" from the upper levels, and if so they CANNOT be used as "wet vents". If that is REALLY 18' from wall to vented stack, then it is too far away from the vent. The downstairs tub is NOT vented, and technically, neither is the toilet.

Wisconsin Plumbing Code Link

In Wet Venting, water closets must connect downstream of all other fixtures within the bathroom group.
added by Terry

Click to expand...

The only horizontal wet vent allowed in WI is a bath group through the lavatory. Whether you can use an AAV will be based on the local inspector, but you should be prepared to show why a proper vent cannot be installed.

so if i vent the tub & shower drains into the lav AAV i'm good to go? the w.c. is only 2' from the main 4"c.i. line - can i just dump it in there without a vent? thank you for your help.

An AAV is not a bandaid that will fix everything! In some places, they aren't allowed at all. It is a one-way air vent, and sometimes, you need to be able to let air out of the system, not just in, so no, it may not work properly. What would work anywhere to all codes would be to run a vent up either all the way to the roof, or into the attic, then tie into another vent in the attic before it goes out of the house. Keep in mind that a drain line could be a vent to things above, but once a line becomes a drain, it cannot be a vent.

i may be able to get a vent up to the attic thru a closet. there would have to be some horizontal vent lines in the basement (allowed?) to connect the tub,shower & lavs. would it matter if the vent lines were under the concrete and then up at a single location - or run vents to the closest wall & tie them together up under the joists and then up and out the attic? will the w.c. be ok dumping directly into the 4" from 2' away with no vent? thank you.

Every trap must have a vent including the W.C. The tub/shower/w.c. can be wet vented through lavatory. The vents must rise vertically until they reach a point no lower than 6" above the flood rim of the lavatory before they can they turn horizontal. The horizontal portion of any vent must be pitched towards a fixture drain. Vents can all tie together either at the basement ceiling or in the attic so that only a single vent through the roof is required. The WI plumbing code is pretty clear on what you are allowed to do.

This type of work requires a permit which can be obtained from your local municipal office. To obtain a permit, you will need to submit an isometric diagram of the plumbing that you intend to install and in some places a bill of materials will also be requested.

If you place into use any new plumbing system without approval and inspection, the municipality can deny occupancy of the residence until the unapproved system is removed. It is in your best interest to do this right the first time, or not at all.

Wisconsin Plumbing Code Link

cacher, thanks for the constructive comments.

basement bath venting

I'm posting again to see if i have learned anything about adding a basement bathroom. i've given up "wet venting" and hope this plan is correct & WI code compliant. thanks for all previous comments and anything helpful on current plan

Direct link because the other was too small.

You we're given a bunch of great advice, why create a new thread.

Basically you're going to be able to wet-vent, but only if you do it properly.

My intention was to rip nothing, but your original plan failed to meet any plumbing standard.

If you draw an isometric diagram, it will make it much easier for everyone.


There is free printable isometric graph paper all over the internet which makes drawing quite easy.

dlarrivee & cacher say i can wet-vent, but do not offer a "how to" clue. another says it is way too far to the existing vent stacks and it won't work-period. if i were a master plumber i wouldn't be asking for help. maybe the forum format works only for clogged sink & leaky faucet questions? how does one beg on the internet?

thanks, i understand wet venting. the problem that has been pointed out is that my wet stack on the 4" drain line is too far away at 18'-20'. do you have a different opinion?

oldnorskie in your post yesterday you seemed to complain. But cacher_chick had posted a drawing an hour earlier, and I think that drawing deserves a compliment and a "thank you".

You are the only one in the world who is motivated to compare that diagram to your needs and to your real-life situation. Don't go expecting a number of people to go try and make head or tail of your first diagram, and then compare it to the one posted by cacher_chick, and then comment on the possible differences, and also to try to refine it or to offer alternatives. You already have one person doing a good deed for you, and you ignore it and post a whine. Hmmm...

oldnorskie in your post above you ask "do you have a different opinion?". Is this addressed to dlarrivee? Reviewing his other posts you'll see he often asks one-liners and in so doing obliquely points towards a new idea. That's about the extent of it.

oldnorskie, one week ago you posted under the name oldnorskie in a garden web forum that was supposedly for plumbers. All you got was one guy telling you again and again the same thing as what you got here: i.e. that no, a wet vent is not a wet vent when the pipe is YEA long. Now you say you know wet venting. OK, great, you learned something about wet venting in the last ten days. BUT only you can pick up the threads of the discussion and take it in the direction you want it to go. Comment on the nice clear drawing you got yesterday when someone posted it. That drawing is SO clear and complete that it makes me cry. I wish I had had such good work done to help me when I was starting out.

Since cacher_chick pointed out that "your original plan failed to meet any plumbing standard" I guess it becomes clearer and clearer why this thread is not getting any traction, and also last week's thread in the other forum. We have an OP who whines, who doesn't do his homework until a few days later, who has a complicated situation that only he can tell us about, but won't.

Hope this helps.

"YEA long" is no help. and i do appreciate cacher-chick's isometric but it seems the layout is so basic that a plan view is sufficient. real plumbers; is there such a thing as a finite distance allowed from the 4" wet vent to where my 3" layout intersects the 4" main? also, it seems important to mention again that upstream from my 3" layout is another, separate wet-vent stack serving a standard bath. lots of "free air" in all those pipes? thank you.

The maximum allowed distance between a trap and it's vent is listed on table 82.31-1. This is the distance you must adhere to regardless of if you are using a wet vent through the lavatory or individual dry vents.

A drain line or drain stack connected to any other fixture in the house cannot be used as a wet vent.

cacher, thank you very much for the pointer - it was just what i needed. b-y

cacher_chick said:

My intention was to rip nothing, but your original plan failed to meet any plumbing standard.

If you draw an isometric diagram, it will make it much easier for everyone.

There is free printable isometric graph paper all over the internet which makes drawing quite easy.

Click to expand...

I know this post is old and I am not a licensed plumber, rather trying to check my knowledge for educational purposes. I'm seeing issues with this drawing, please correct me if I'm wrong: shower is 1.5" instead of 2", 1.5" vent in the middle of the drawing should be 2" (above the word "TUB"), & the dry vent after the shower cannot go horizontal. If I'm correct, what would be the easiest way to correct the horizontal dry vent after the shower before it turns up to go up the wall? Thanks!!