Hi - we want to add a bathroom in our attic, right above existing bathrooms, but can't do 'the right thing' with running a new vent stack line to tie in fixtures below the existing units. My question is:

If we put in this bathroom, which would be wet venting everything, what problems will it cause?

We would likely use this attic bathroom about 40 times per YEAR, and would go back in about 2-3 years to 'fix' the DWV lines when we redo the existing bathrooms.

Thanks, Matt

Good morning Matt,

You may install your bath group and keep it legal by discharging the toilet, (3"line) into the existing vent stack and tying in the lavatory (2" line)to the toilet discharge and connecting the shower or tub, (If you plan on one) into the lavatory drain line. You will vent your group by running up from the tee that stubs out the lav and tying it back into the existing stack as a revent, or you may run it out the roof as a separate vent. The tub/shower will be wet vented back through the lav drain line. More questions? I'm as close as a click. Good luck, Tom

Great news! But do I run into any problems by having the waste from the attic 'run into' the waste lines from the fixtures below it?

I'm just worried that I will create some kind of problem with the lower bathrooms by having the upper bath group drains meet inline. I've tried to make this quick little diagram to show what I mean in case it was not clear.

Thanks again, Matt

| (roof vent)
|
| Bath group (attic)
|-----'
|
| Bath group (2nd floor)
|-----'
|
|
|-----(to sewer line)

As long as the bathroom groups are vented the common stack's both acceptable and within code. Just revent the attic group back and you'll be OK. Cheers, Tom

Okay, now I think I have the right question to ask...

The issue is that the lower bath group will not be really be vented... it would be (wet?) vented up to the attic bath goup (and then out to the roof).

What problems will I cause by not having a proper vent stack for the lower bath group?

Sorry to be dense, you've been nothing but helpful!

You will have to run the lower vent up to 6" over the top of the highest attic fixture and revent back into the attic vent or out of the roof. This is not a wet vent set up. Cheers, Tom