using section of pipe for both drain and vent
 

my powder room will be right below my bathroom on the floor above. there is a vent pipe coming into the bathroom from the roof and i was gonna tie into it to discharge the bathroom sink and bath tub. then i was gonna use the same pipe for the powder room sink to get vent and also discharge. so the portion from the roof to the bathroom would be vent only but from there to the powder room sink it would perform both vent (for the powder room) and discharge (for the bathroom above). below it would be no more ties into only flow into the main in the basement below. i was wondering if this dual use for both vent and drain in that portion is OK. if it is a problem, i can run double pipe in the portion so that the vent and drain don't mix but obviously, the former design would be simpler.

thanks

No it is not code compliant, what you are describing is a wet vent. The vent for the powder room should be piped above the discharge drain of the bathroom and can then be tied back into the vent before it goes through the roof.

I've seen wet vents done before, are they not code compliant everywhere? Can you wet vent a toilet?

thanks a bunch !! it shall be no problem to do it that way, just a little more pipes and joints.

:thumbsup:

Wet vents are allowed often. You just have to meet certain code criteria. A couple of examples for my area would be:
vertical wet vent only
2" min. pipe size
fixtures must be on the same floor and no more then 6ft apart

I'm sure the IPC reads differently as will a Canadian code.
Its best to consult your local inspector.

The OP described venting the lower floor powder room into the drain of the bath above, this is a no, no. Yes wet vwenting is allowed with restrictions but I was answerimng the OP's specific case.

Got it, no wet-venting to a fixture that is a floor above the one you want to add.