Joining vent pipes in attic

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by muzz, Aug 17, 2008.

  1. muzz

    muzz New Member

    Messages:
    21
    I have a 1 1/2" vent protruding thru my roof now, have added a 3" vent with a bath remodel that is waiting to be finished capped in the attic. My original plan was to tie both of these in together and run thru the roof in the existing hole, it would mean a 5' horizontal run with the 3". I am reconsidering this, now thinking I should run the 3" straight thru the roof, not a fan of putting another hole in the roof, but...
    Should I:
    --leave the 1 1/2 as is; run the 3" straight thru (would it make sense to tie the 1 1/2 in horizontal anyway?)
    --take out the 1 1/2 thru the roof and repair the hole in the roof and vent the 5 feet horizontal over to the 3"
    I live in Minnesota, and the weather can be severe, I believe that the smaller pipe frosted up in the winter, or got plugged with snow in the heavy snow years.
  2. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    Not sure where you live, but most parts of the country require 4" through the roof.
  3. Terry

    Terry Administrator Staff Member

    Messages:
    15,005
    Location:
    Bothell, Washington
    Then I would go with the larger pipe.

    I'm in the Seattle area, so the concerns are not the same. Unless we are plumbing at the ski areas.
  4. muzz

    muzz New Member

    Messages:
    21
    so you are saying to take out the 1 1/2, or could I leave it and tie the two in?

    thanks
  5. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    Yes you can
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    Patch the hole for the 1-1/2" one, run it over to the new pipe. You might consider bumping the penetration to 4".
  7. muzz

    muzz New Member

    Messages:
    21
    thanks jadnashua, I guess I was hoping to leave the 1 1/2, but it makes sense to take it out.
  8. Herk

    Herk Plumber

    Messages:
    547
    Location:
    S.E. Idaho
    I think it would be easier to put a new penetration through the roof and simply go straight up.

    Running from one pipe to another requires support and grading, and probably uses more pipe and fittings. If you were putting in a newer, smaller pipe it might be different, particularly if your roof has clay tile or shakes on it. But if it's shingles, cut a hole and flash it, fer crineoutloud. You have to make a bigger hole anyway.
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    Or, you could make the existing hole bigger and join there. Or just put a second hole in the roof.
  10. muzz

    muzz New Member

    Messages:
    21
    The reason I was considering tying them in was because of the years that we get heavy snow, the small vent may get plugged or frosted over for a period of time; I thought that tying in to the bigger vent would take care of that? I figured it would be better to go straight up with the 3" rather than doing a horizontal to the smaller and tying in there. Its only a 5 foot run...

    Thanks for all the input.
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,641
    Location:
    Cave Creek, Arizona
    vent

    You can do it any of the ways you mention, or possibly a couple of others you did not think of.
  12. muzz

    muzz New Member

    Messages:
    21
    HJ, could you enlighten me? Curious to know what you have. I still have some time before I am going to tackle this; the weather has turned hot here for some strange reason, been pretty cool all summer. Enjoying it while I can.
  13. comp1911

    comp1911 New Member

    Messages:
    5
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