Venting question

Discussion in 'UPC Plumbing Code Questions' started by tomski, May 1, 2021.

  1. tomski

    tomski New Member

    Joined:
    Feb 13, 2021
    Location:
    auburn, CA United States
    I've attached a layout of my proposed plumbing for an addition. I'm in California so UPC.

    I've read that a 2" vent can take care of 24 DFU's. I have a total of 8 DFU's so I thought I could combine the two 2" vents in the attic to one 2" vent through the roof.

    However, I've also read that the area of all the vents must be greater than the area of the main drain. My main drain is 3" so by this standard I need 7.07 sq. inches. Even if I use a 2" vent through the roof for the kitchen sink and another 2" vent through the roof for my bathroom group I am still short of the 7.07 sq. inches. Am I missing something or do I have to add another vent pipe somewhere? Thanks for your input.
     

    Attached Files:

  2. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    Through the roof, two 2" vents and a 1.5" vent.
    The kitchen sink is getting the 1.5" vent, and the bathroom group is the 2".
    You have other plumbing in the home, right?
     
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  4. tomski

    tomski New Member

    Joined:
    Feb 13, 2021
    Location:
    auburn, CA United States
    Yes there is other plumbing and vents in the main part of the house.....forgot about those so that would take care of the total vent area.

    Just to clarify, you said 2 2" vents and one 1.5" vent. I assume you meant one 2" and one 1.5"?
     
  5. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Under the UPC, if you have 3 WCs or less, the minimum size building drain is 3". With 4 WCs, the minimum size building drain is 4". The total vent area through the roof has to be at least the minimum size building drain.

    For 3" minimum area, you could obviously do a 3" vent. Or you could try (2) 2" vents, but 2^2 + 2^2 = 8 < 9 = 3^2. So that's not quite enough, you'd need to use (2) 2" vents and (1) 1.5" vent, which was Terry's point.

    For 4" minimum area, you could do a 4" vent, (2) 3" vents, (1) 3" vent plus (2) 2" vents, (4) 2" vents, (3) 2" vents and (2) 1.5" vents, etc.

    Cheers, Wayne
     
  6. tomski

    tomski New Member

    Joined:
    Feb 13, 2021
    Location:
    auburn, CA United States
    Ahhh. I'm so focused on the new plumbing, I keep having tunnel vision. I wasn't realizing Terry was talking about the house in total, not just the new addition. Sorry, I'm usually not so dense. Thanks again to both of you for the help.
     
  7. Nick_A

    Nick_A New Member

    Joined:
    May 19, 2021
    Location:
    Iowa
    Hello, this thread is helpful to me, thank you. On the vent size requirements, is this requirement for the size at the interface with the roof, or the size of the vent stack in the attic space? Thinking in terms of the upsizing one inch at the roof due to freezing temps in the winter.

    Thanks
    Nick
     
  8. Tuttles Revenge

    Tuttles Revenge In the Trades

    Joined:
    Oct 15, 2014
    Code does call for upsizing a pipe size for the potential freezing of condensation in a vent at the roof. The upsizing should occur at least 1ft below the roof but also within an insulated space.. so potentially the entirety of the attic space starting at the insulated portion. I had to look that up since we don't deal with climate that cold.

    The discussion was originally about the proper sizing of venting at a group of new fixtures in an existing house. The OP's drawing was perfect for horizontal wet venting the bathroom and separately venting the sink in wich they could be combined and vented through the roof as 1 penetrations.
     
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