Hello, I added a new 2nd story full bath. I had a 3 inch pipe main drain coming out of the ground behind my laundy room. On the side the laundry drains into this pipe with a trap. On the top was a 2 in pipe that was the vent. I took this vent out and made it 3 inch all the way up to the top and ran the line to my new bath. I then went back to 2in and went out the roof with the vent. I vented all my new fixtures correctly with the 2in vent that is behind the bath.

My problem is I thought I was going to wet vent the laundry downstairs with the 3 inch pipe. I forgot to take into account that water falling from the 2nd floor pushes air differently. Should I add a 2in vent at the bottom and go out the roof. Like the old one except on the side? And should I vent before it goes down the wall and tie into the new vent line I'm going to run up the wall? Or am I totally wrong and need to do something else?

Thanks!!

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I thought I was going to wet vent the laundry downstairs with the 3 inch pipe

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But what you really did was to discharge major fixtures past a unvented minor one. This is against code and not very good practice.

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Should I add a 2in vent at the bottom and go out the roof Like the old one except on the side?

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You should add a vent on the laundry. You may run the new vent out the roof, revent back into a existing roof vent in the attic or revent back into a existing dry vent at least 6" above to flood rim of the highest fixture on that vent. OR** If local codes allow, you could install a AAV,( air admittance valve) just downstream from the laundry trap.
Your choice! But you're going to hafta vent that laundry. Good luck, Tom

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Originally Posted by Paul1279

Hello, I added a new 2nd story full bath. I had a 3 inch pipe main drain coming out of the ground behind my laundy room. On the side the laundry drains into this pipe with a trap. On the top was a 2 in pipe that was the vent. I took this vent out and made it 3 inch all the way up to the top and ran the line to my new bath. I then went back to 2in and went out the roof with the vent. I vented all my new fixtures correctly with the 2in vent that is behind the bath.

My problem is I thought I was going to wet vent the laundry downstairs with the 3 inch pipe. I forgot to take into account that water falling from the 2nd floor pushes air differently. Should I add a 2in vent at the bottom and go out the roof. Like the old one except on the side? And should I vent before it goes down the wall and tie into the new vent line I'm going to run up the wall? Or am I totally wrong and need to do something else?

Thanks!!!

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You should never downsize a vent -- If you brought it up as 3", then it should exit the building as 3".