VTR sizing

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by DavidTu, Dec 19, 2010.

  1. DavidTu

    DavidTu Member

    Messages:
    239
    Location:
    Seattle, WA
    In a moment of hubris :cool:, I had two 2" VTR roof jacks installed for a 3" drain. :eek:<doh!

    [Mea culpa: I am aware of the area requirements for VTR but I didn't have my book or calculator with me and I knew that two 3" pipes > 1 4" pipe, and same is true for all other pipe sizes relative to the next size up so I errantly ASSUMED that the same held true for two 2" > one 3" in area.... EXCEPT, it turns out it's not: 2x2" = 6.28si vs 3" = 7.06si).]

    My venting is mainly all 2" runs. I'm in Seattle and the Chief Inspector has previously told me that they do NOT require a continous run from the sewer through the roof at full-size of the sewer (ie. 3" from sewer through roof). Rather, as long as each fixture is appropriately vented and as long as the accumulated dfu's are within spec all is good (provided we meet the area requirement which we did not do).

    My question is: a) will the inspector definitely require me to upsize one VTR to 3" (leaving other 2")? ... i.e. should I see if it sneaks by or just go ahead and do it now! and (b) is there any real-world benefit to doing this inasmuch as venting to satisfy the dfu's is easily handled by 2" vent pipe (24 dfu capacity, 13 used) and really all that will happen is in the attic I'll upsize the 2" pipe to 3" when I join a couple of 2" pipes there. NOTE: I do plan to use a AAV for kitchen sink.

    FYI: one 2" VTR is serving a toilet + lavatory (4 dfu), the other is serving laundry tray & clothes washer standpipe, toilet, lavatory, tub/shower, and a kitchen sink w/ disposal + dishwasher vented on AAV (13 dfu including KS)
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,321
    Location:
    New England
    Some places require the vent to be larger because of potential frost buildup. That probably isn't an issue in Seattle.
  3. DavidTu

    DavidTu Member

    Messages:
    239
    Location:
    Seattle, WA
    So is the consensus that I'd be OK leaving both at 2"?

    Btw, if I could locate some 2.5" pipe it would work for the area requirement AND fit inside the '2-inch' roof jack since it is a lead jack it seems larger than 2" abs pipe and looks like it could accomodate the 2.5".

    (Also, is there some minimum length I'd have to have 3" pipe inside, were I to upsize the jack?)
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,263
    Location:
    Cave Creek, Arizona
    It would have to be 3" from the point of juncture of two other vents. I assume this is a tile roof, so adding a 1 1/2" vent may not be a possibility, but that would satisfy the inspector. IF he only sees TWO 2" vents he will know the area rule was not met. In the future, when you want compare areas, just square the radius, (forget about pi, since it is a constant), and do the computations.
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