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Main stack venting

DIYJester | Posted in Building Code Questions on

I’m finishing tying in an addition to my existing slab on grade home and found the main stack vent on the existing house is about 6″ into what will be a hallway.

The original house had a 3″ main stack vent off the master bath, near where the drain exits the house to the septic. There is also a 2″ vent on the other side of the house connected to the kitchen and another full bath. There is a 3rd full bath in the middle of these two vents. The original master bathroom piping has been capped and covered with concrete, except the main stack vent.

The addition plumbing has a master bath and a 2″ vent stack” off this and a 2″ vent off the new drain stack.

Is it possible to cap the old master bath main stack vent since no fixtures are now withing the code requirements and are technically being vented closer to the fixtures? It is my understanding that for smaller pipe in the 1.5″ and 2″ range IRC/IBC only allows the vents to be 6-8′ away. With that said this main vent would be 30′ feet from the nearest fixture.

I made a crude picture to try and help.

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  1. tommay | | #1

    Not sure where you are located, but every house has to have a minimum 3" vent stack for the main drain through the roof. Other individual vents must be 2" minimum through the roof. Hopefully you can offset the main stack to get it into a wall after framing the new hallway. Or cut the slab and move the wye fitting to where it is needed.
    The 6-8 ft you mention is the distance from the fixture trap, on the horizontal, to the vertical vent. The pipe size depends on this distance.

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