Vent Size Question

[neils]

Updating my kitchen and adding a utility sink. Our town follows IRC 2018. Checking code and references I don't see a clear answer for my question. I have a 2" lateral that will serve a washer, utility sink and kitchen sink (5-6 DFU's depending on grouping). The 2" drain line is good for 6 DFU's but I'm not sure about the 1-1/2" vent line circuit. My modification would be much simpler if I could keep 1-1/2" vent line and minimize 2".

Can I keep it all 1-1/2"? Or do I need to upsize the center vertical stack and main line out to the roof 2"? Thoughts appreciated.

Note I'm aware of cleanouts, fittings, etc.. The attached simplified diagram is just for the venting question.

PS: Great forum. I've learned a lot from it in the last month. Truly Terry's legacy.

 

[wwhitney]

A 1-1/2" vent is fine, see P3113.1 https://up.codes/viewer/tennessee/irc-2018/chapter/31/vents#P3113.1

Note that your utility sink venting depends on Circuit Venting P3110. https://up.codes/viewer/tennessee/irc-2018/chapter/31/vents#P3110

As such, the 1-1/2" vent at the san-tee is superfluous. You only need two dry vents, the one just downstream of the kitchen sink, and the one for the lav.

if you want to individually dry-vent the utility sink, then the utility sink fixture drain should needs to proceed separately and horizontally to the stack and connect above the kitchen sink drain. Then the middle vent riser will dry vent the utility sink. And the kitchen sink fixture drain would be free to drop down anytime after its own vent takeoff.

Cheers, Wayne

 

[Sponsor]

 

[Jeff H Young]

The circuit vent is between the 2 uppermost fixtures, It appears the vent downstream of the utilty sink is unnessesary

 

[neils]

A 1-1/2" vent is fine, see P3113.1 https://up.codes/viewer/tennessee/irc-2018/chapter/31/vents#P3113.1

Note that your utility sink venting depends on Circuit Venting P3110. https://up.codes/viewer/tennessee/irc-2018/chapter/31/vents#P3110

As such, the 1-1/2" vent at the san-tee is superfluous. You only need two dry vents, the one just downstream of the kitchen sink, and the one for the lav.

if you want to individually dry-vent the utility sink, then the utility sink fixture drain should needs to proceed separately and horizontally to the stack and connect above the kitchen sink drain. Then the middle vent riser will dry vent the utility sink. And the kitchen sink fixture drain would be free to drop down anytime after its own vent takeoff.

Cheers, Wayne

Thanks for the thoughtful reply.

Yes that center vent line is redundant, but it is existing so I planned to leave it in place. The drain line to the kitchen sink is new. The sink is in a peninsula and could use an AAV, but is close enough to the wall for its own vent. I thought it better, for inspection and reliability, to add the left vent line and tie it into the roof vent line above.

Best, Neil

 

[Jeff H Young]

I think wayne is saying that the utility sink is adequately vented . Ive never run a Circuit vent system havent ever seen them in practice . Havent really reviewed this type system but sounds like it may actually be a legit circuit vented system as drawn. the rendundant vent could be a relief vent but nothing shows that a relief vent would be required.