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Pipe Venting

The right way to rough in a future bathroom

Richard Trehewey holds a toilet

In an old house we purchased recently, we're remodeling the kitchen and bath that are adjoined. While I'm at it, I want to rough in plumbing for a second bathroom directly above the existing one. I'd like to cut the existing four-inch vent stack and take my new drains off of that and then continue the vent through the roof. Taking into consideration that the first floor bath will now be wet-vented, would you say this is properly vented?

— Al, Chicago, IL


Richard Trethewey replies: If you're cutting the stack at the first-floor level, then the kitchen and first floor bathroom should have vents that either continue through the roof or reconnect to the stack at a point above the highest fixture in the building. These vents can be run individually or tied together with single pipe that goes up to the high point. The bathroom on the first floor can certainly be wet-vented as long as the vent ties in as noted. The second floor bathroom, when and if you do it, can be stack vented so that the remaining full-size stack acts as the vent for the bathroom group.


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