Another Venting Question

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Arca, Oct 10, 2020.

  1. Arca

    Arca New Member

    Joined:
    May 19, 2020
    Location:
    Ohio
    Hi everyone,

    I am running a new 2" vent for a master bath and have run into a little problem.

    I am using an old vent's roof location. I raised the ceiling of the master to 8', and have now discovered that I do not have the proper 1' clearance from the roof to my 3x2 reducer. I am at about 7.5" from the "high side" of the vent.

    My question is...can I extend that 3" pipe length horizontally? I would come down 7.5" from the roof, glue a 3" 90 and then continue with 3" pipe the needed length to my reducer.

    I know this may not work, but with that being said can someone provide me with a little education on this section of plumbing code? I understand it is for frost and condensation?

    Thanks everyone!

    EDIT: Here is a sketch.
     

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    Last edited: Oct 10, 2020
  2. James Henry

    James Henry In the Trades

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    Jul 23, 2019
    Occupation:
    Plumber
    Location:
    Billings, Montana.
    Upload a sketch of your proposition and someone can answer your question.
     
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  4. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Can't you just put the 3x2 reducer in the wall below the roof penetration?

    Here's the relevant code section:

    https://up.codes/viewer/ohio/ipc-2015/chapter/9/vents#903.2

    If your insulation is in the ceiling rather than between the rafters, that section requires the 3x2 reducer to be at least 12" below the bottom of the ceiling joists.

    Cheers, Wayne
     
  5. Arca

    Arca New Member

    Joined:
    May 19, 2020
    Location:
    Ohio
    Thanks Wayne, we are going to spray foam in between the roof rafters, not ceiling joists. Will that make a difference?
     
  6. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    I am not saying that a reducer is or is not OK where your sketch shows, but I think it should be a
    3" x 2" PVC Schedule 40 Eccentric Reducer [​IMG] A regular reducer would leave a little mosquito-breeding pool I fear.

     
  7. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    I would start measuring the 12" from the warm side of the spray foam. That's the thermal envelope.

    What's going on to the right of your sketch? I'd consider making the entire horizontal run 3". I think there's some code language about the vent being arranged to drain, so any reducer on the horizontal would be required to be eccentric.

    Cheers, Wayne
     
  8. Jeff H Young

    Jeff H Young In the Trades

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    Feb 27, 2020
    Location:
    92346
    I would run 3 inch vent horrizontal then reduce on the vertical. Never seen a eccentric reducer in a dwv system used I dont think it meets code but it might
     
  9. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    That would look better.

    Arca, 45 off of vertical is considered vertical. So you could put a 45 where you have the 3-inch 90 drawn, and go down again with another 45.
     
    Jeff H Young likes this.
  10. Arca

    Arca New Member

    Joined:
    May 19, 2020
    Location:
    Ohio
    Thanks everyone...great idea on the 45s...that will give me my 12" of vertical below the roof.
     
  11. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    A couple comments:

    - If you are able to use a reducer coupling on the 45 degree section, then you won't create any region that can collect water:

    https://www.supplyhouse.com/Spears-P102-338-3-x-2-PVC-DWV-Reducer-Coupling

    - The 12" length is supposed to be "inside the thermal envelope," which isn't so precisely defined. If you have, say, 6" of spray foam up against the plywood roof deck, I would conservatively say that the thermal envelope is located 6" below the roof deck, so you'd need 18" of 3" pipe below the roof deck. It would be reasonable to argue that the thermal envelope is the middle of the 6" insulation thickness, so you'd only need 15" of 3" pipe below the roof deck. I would argue against using only 12" of 3" pipe below the roof deck.

    Cheers, Wayne
     
  12. Arca

    Arca New Member

    Joined:
    May 19, 2020
    Location:
    Ohio
    Got it and agree, Wayne. I am probably going to go higher than the minimum 12 inches outside of the roof in order to get a good 3" run below the insulation. Thanks for all your help sir.
     
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