I am having a bathroom added to the third floor of an old Victorian home. The bathroom will have a shower, sink and toilet. The room is situated between two existing vents, but because this is basically an attic floor, I think they may be too low to be used by this new bath. They are so low that I believe the sink trap will be in line with the penetration.

How high does the roof penetration need to be in comparison to the drain?

Hi Weller...

Vents need to connect into vent stack at 6 inches above the flood level rim of the highest fixture being served on a particular floor. In this case, as in most, the lavatory will be the highest fixture so you can at a MINIMUM connect into the stack vent or penetrate the roof at 42" off the finish floor. All other vents (if any) will connect into this vent and pitch back toward the plumbing so rain water can drain back to the plumbing system.

Sink drain/ptrap cannot be in-line with the roof penetration as drain could get blocked and instead of showing up as a clogged drain it would simply overflow into the vent and out the roof! That make sense?

For a bathroom on the 3rd floor you will most likely only need 1-2" WET VENT. This wet vent will come from the toilet pipe and will pick up the shower drain as it runs by to pick up the lavatory. The pipe will then pick up the sink and run full size 2" up the wall and out the roof.


Let us know if need more info. Here...

MARK