Hello,

I am installing a toilet, sink and tub into my attic space that I am finishing. My question is: how can I tie into the existing 4" stack without affecting the fixtures below. Presently the stack acts as a vent for the lower story fixtures. Will I need to re-vent the lower fixtures in order to use the stack as a downpipe to the main sewer line in the basement?

In the attached images (if I can get them to load) the top of the two diagonal pipes was labeled "vent" by the previous owner of the house. This ties in to the lower diagonal pipe about 8" above where they meet the joists. The vertical pipe leads to the first floor toilet which is straight above. I've read in other posts about using a "wet vent" in the attic. What is the scoop on "wet venting"? Is this applicable to my application?

Thanks,
Charles

Hey Charles,

"Will I need to re-vent the lower fixtures in order to use the stack as a downpipe to the main sewer line in the basement?"

If you connect the attic bathroom group to the attic vent you will have to disconnect the lower vents on this stack and run them up to the attic where you can revent back to the existing roof vent.

"I've read in other posts about using a "wet vent" in the attic. What is the scoop on "wet venting"? Is this applicable to my application?"

Wet venting is using a existing drain line as a vent. Most bathroom groups are roughed in like this.
Toilet connects to sewer main or stack vent. The toilet wet vents through the lavatory vent. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book. More questions? I'm as close as a click. Regards, Tom