Vertical wet vent sizing question

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Natimus

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Hi All,
I have a question about sizing a wet vented section of a vertical drain and also the horizontal drain section that immediately follows. As you can see in the drawing, I have a short section of vertical wet vent between the tub and a laundry sink on the other side of the plumbing wall. After reading the California plumbing code, I concluded that the wet vent section must be 3" pipe (1 pipe size larger than the proper size for both fixtures on the wet vent). Does that then mean that all of my drain sections immediately downstream of the wet vent must also be 3" ? Or can I reduce to 2" once the wet vent is finished? It feels wrong to reduce to 2" from 3" even in this case. Thoughts? Is 3" even the correct sizing of the wet vent?

Much appreciated!

Nate
IMG_7213.jpeg
 

wwhitney

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Yes, the wet vent would need to be 3" (or 2-1/2"), because the laundry sink's minimum drain size after the vent is 2". And yes that means that all downstream drains would need to be at least 3".

However, you have a problem with the above configuration. Horizontal wet venting is limited to bathroom fixtures. So the horizontal drain between the tub/shower and the WC can not be a wet vent for the WC, since it is carrying the laundry sink. That leaves your WC unvented.

The typical solution would be to keep the 2" laundry drain separate from the 2" tub/shower drain, with the tub/shower drain joining the WC to wet vent it, and the laundry sink drain joining in downstream of the WC. The tub/shower needs a 2" vent to wet vent the WC, while the laundry sink needs only a 1-1/2" vent. Those vents could join 6" above both fixture flood rims.

Cheers, Wayne
 

Natimus

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Yes, the wet vent would need to be 3" (or 2-1/2"), because the laundry sink's minimum drain size after the vent is 2". And yes that means that all downstream drains would need to be at least 3".

However, you have a problem with the above configuration. Horizontal wet venting is limited to bathroom fixtures. So the horizontal drain between the tub/shower and the WC can not be a wet vent for the WC, since it is carrying the laundry sink. That leaves your WC unvented.

The typical solution would be to keep the 2" laundry drain separate from the 2" tub/shower drain, with the tub/shower drain joining the WC to wet vent it, and the laundry sink drain joining in downstream of the WC. The tub/shower needs a 2" vent to wet vent the WC, while the laundry sink needs only a 1-1/2" vent. Those vents could join 6" above both fixture flood rims.

Cheers, Wayne
Thanks so much Wayne. I appreciate the response. My WC is only 5' from the main stack with a vented lav in between. I recall that anything less than 6' is ok for a WC. Does that sound right or does the WC have to be on it's own branch for that to be true?
 

wwhitney

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A drain which is horizontal and is to function as a vent (wet vent) must be draining only bathroom fixtures.

So eliminate the laundry sink and your WC would be wet vented by the tub. Eliminate the laundry sink and the tub, and your WC would be wet vented by the lav. But connect the laundry sink as shown and that horizontal drain can no longer be used for wet venting.

Cheers, Wayne
 

Natimus

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A drain which is horizontal and is to function as a vent (wet vent) must be draining only bathroom fixtures.

So eliminate the laundry sink and your WC would be wet vented by the tub. Eliminate the laundry sink and the tub, and your WC would be wet vented by the lav. But connect the laundry sink as shown and that horizontal drain can no longer be used for wet venting.

Cheers, Wayne
Got it. Thanks for the quick responses, Wayne. I appreciate the help.
 
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