double bath DWV

I'm trying to figure out the most efficient DWV for our back-to-back bathrooms. We're under IPC 2006. Does this iso look correct? I would be using a double fixture fitting for the back-to-back lavs. Can I take a common vent for both toilets off a wye between them? Would the bathtub be properly wet-vented off the lavs if it were within the required distance?

Also, I'm unsure about how to connect the bathtub drain/wet vent to the main drain. I read in a plumbing book, which I think was based on UPC, that you can't roll your wye above a 45 degree angle with a wet vent because the falling water might cut off the flow of air in the pipe. Is that correct? Thanks for your help.

IPC is fairly close to my code, so everything looks pretty good to me....except for the bathtub.

Basement_Lurker said:

IPC is fairly close to my code, so everything looks pretty good to me....except for the bathtub.

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I'm trying to get a grasp on wet-venting, and the IPC regs seem pretty lenient as long as all of the pipes are the right size and the traps are within the required distances. Is there a reason why the bathtub wouldn't be wet vented off the lavs?

The bathtubs would be "wet vented" off the lavatories ONLY if it were connected to their drain pipe, ideally, into the vertical section of it. Just having water flowing past a drain connection does NOT make it wet vented. And, a toilet flowing past an unvented tub or shower connection is ALWAYS a no/no.

hj said:

The bathtubs would be "wet vented" off the lavatories ONLY if it were connected to their drain pipe, ideally, into the vertical section of it. Just having water flowing past a drain connection does NOT make it wet vented. And, a toilet flowing past an unvented tub or shower connection is ALWAYS a no/no.

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I'm so confused by wet venting. I thought that the IPC allowed for horizontal wet vents, so that the wet vent for the bathtub would extend from the drain for the lavs through the main drain to the point where it connects to the bathtub trap arm. I thought that the wet vent portion just had to be large enough to handle both the discharge from the upstream fixtures while carrying enough air to protect the traps of the wet-vented fixtures. Here's a link to an ICC journal article with a simlar arrangement on page 4.

I can see how you are confused. That link you provided shows a HORRIBLE example of wet venting. Wet venting properly is a difficult concept to understand and implement properly. Your drawing was pretty good (on paper), except for the fact that flushing either toilet, and especially both, would siphon the tub's trap....which would make you a very naughty DIYer!

The problem is that you think the IBC is a "plumbing code", but it is really a document written to allow plumbing to be installed a inexpensively as possible. That "code" has very few things which it does not allow. That drawing of the toilets and shower into a horizontal line would NEVER pass under any "real" plumbing code. The IPC and UPC were all set to merge into a single code, until the IPC contractors found out they would have to change the way they did plumbing. Then they withdrew their ratification of the merger.

put a 3 x 2 combo looking up, put a sanitary tee looking in the detection of the tub rough in for your p-trap, then re-vent all the way back to your vent stack.

I hope you realize it is easier to tell someone how to fix a faucet or stopped up drain, than to give directions about doing a complete bathroom installation over the Internet. Especially, when the exact way we would do it would depend on the situation which we CANNOT see.

Will Rogers Plumbing said:

put a 3 x 2 combo looking up, put a sanitary tee looking in the detection of the tub rough in for your p-trap, then re-vent all the way back to your vent stack.

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I think that's what I'll end up doing. I was interested in trying a wet vent, but it sounds like it wouldn't work in this arrangement.