Hello. We’re adding a second floor powder bath. It has a vaulted ceiling/steep pitch roof. So the plan is to run a 3” pipe horizontally to catch the toilet approximately 4 ‘ between the joist bay and drop it down vertically in a wall space to the crawlspace below. On the vertical 3” pipe will be a 3x2 wye to catch lav drain running below floor joists. Reason being there is space approximately 3” above a false ceiling where we can run this pipe. But in an adjacent joist bay there is a 1-1/2 vent running horizontally that will intersect above this 2” lav waste that runs across to catch another lower floor bath and then exits out the roof. The vent termination is 4-5’ above the the second floor level. Can I tie the 2” lav into the 1-1/2 with a tee at the intersection and use that as a vent for powder bath? The 2” will be horizontal below floor joists and the 3” horizontal pipe for toilet is above that in the joist bay remember. Thank you in advance.
Second floor powder bath vent issue
- Thread starter Stud59
- Start date
wwhitney
In the Trades
If you are asking if you can tie a drain for fixtures on the 2nd floor into a dry vent that is serving fixtures on the 1st floor, definitely not. Wet venting is limiting to fixtures on the same floor.
Cheers, Wayne
Cheers, Wayne
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No it would still be a dry vent. No water would flow through this 1-1/2” pipe. The 2” lav would travel below this under the 2nd joists, as the dry vent is in the joist bay above, perpendicular to it.
wwhitney
In the Trades
OK, second try: if the question is about tying the dry vent(s) for the upstairs fixture to the dry vent from the downstairs fixture(s), you can tie any two dry vents together at an elevation at least 6" above all the flood rims of the fixtures being vented.
If your question is something else, please trying asking it differently, or perhaps provide a diagram.
Cheers, Wayne
wwhitney
In the Trades
Does not work to vent the lav. The lav vent takeoff must be within one trap diameter (1-1/4" or 1-1/2" for a lav) of fall from the trap outlet. So it need to come off in the wall behind the lav.
Also, even if your lav vent takeoff were at an acceptable location, the lav vent couldn't join the existing vent like that. The lav vent has to stay vertical until 6" above the lav flood rim, and any joints between vents similarly have to be above that elevation.
Cheers, Wayne
wwhitney
In the Trades
Not allowed. Can't you run the vent up the wall behind the lav and connect to the existing roof penetration in the attic or ceiling joists?
Cheers, Wayne
In the simplest terms, no. This is a vaulted clg with spray foam , a host of dormer valleys close and steel roof. I’m thinking aav or figure some way to get it from 3” end where toilet is out to dry vent past that and tie in to existing ? Or see end view diagram which may be possible if that works putting vent at a downward slope to catch existing vent stack.
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wwhitney
In the Trades
Sounds like an AAV is the way to go. You can either put it in inside a cabinet under the sink, or inside the wall in a ventilated box. It needs to be at least 4" above the lav trap arm. The AAV will count as dry venting the lav, which allows it to wet vent the WC in the configuration you've drawn.
Cheers, Wayne
Cheers, Wayne
Until now I was too stubborn to figure out that you were under IPC.
You can have VTR vents that tilt either way, so no additional penetration needed. IIRC you need some slope, but it can peak at some point, and drainage can go either way. I think they don't want pure horizontal in the math sense. So while an AAV can work, that VTR (vent thru roof) in img_1995.jpeg would be better.
wwhitney
In the Trades
IPC 905.5 still requires that connections between vents be at least 6" above any fixture flood rims. So if the lav vent would have to turn downward to join the existing vent through the roof, even if it is run at the minimum elevation of 6" above the lav flood rim, then the connection between the lav vent and the vent through the roof would violate IPC 905.5.
Cheers, Wayne
wwhitney
In the Trades
This is called Combination Waste and Vent, but the horizontal oversized drain still needs to have a vent attached to it. This might be possible to do if you can take a vent off the WC fixture drain and get it to rise to 6" above the WC flood rim before joining the existing vent through the roof.
Then the way the lav drain joins the WC drain would need to change (I think it would have to be a horizontal wye), and the lav drain would need to be 2" starting at the point that the lav drain turns downward in the wall behind the lav. Plus there may be some other restrictions I'm forgetting, you'd have to check IPC 915.
Chapter 9 Vents: Vents, Michigan Plumbing Code 2021 | UpCodes
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Cheers, Wayne
Holy moly. This just has to work, there’s no inspection required but I do want to do it close to right if we can. Not saying I want to violate every plumbing code there is but I have to be realistic. I’m a builder by trade so I've seen enough suspect plumbing by licensed plumbers that passed inspection but it was the most impractical way of doing it. And that was coming from the inspector himself.
I interpreted the bending down would be at rafter level.
