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Thread: Vent question

  1. #1
    DIY Member chetwynd's Avatar
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    Default Vent question

    Hi all, I just failed a plumbing inspection because we reduced a 2" vent down to 1.5" just before it goes through the roof. We have two vents very close to each other...I'm not sure which fixture's vent we reduced, but I think we did it order to use the old roof jack and not have to deal with a new one. So, it's either the shower vent or the toilet vent.

    Can anyone tell me what the required size vents are for those, and if reducing down a vent in general is even allowed?


    THANKS!

  2. #2
    DIY Member chetwynd's Avatar
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    Default more details...

    Ok, apparently what it is, it's the shower vent, and it's 2" all the way up, and then 1.5" through the roof. I think the inspector was looking at it backwards, thinking the free air coming into the system through the roof was getting reduced, when in fact it's actually getting bigger. Does this make sense? Talk to me guys...

  3. #3
    Plumber Cass's Avatar
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    Default

    What do you have going through the roof on the other vent that passed.

  4. #4
    DIY Member chetwynd's Avatar
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    Default hmmm

    Not sure...I think the other one is the toilet and it's 2" all the way up. I mean it shouldn't matter if you go from 2" below the roof to 1.5" above the roof right? 1.5" vent is all thats required for a shower, so as long as 1.5" is going through the roof it should be fine, right?

  5. #5
    Plumber Cass's Avatar
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    Default

    3" through the roof is what is required here so it can't frost up closed and not work.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    This is heresay, but it was my understanding that you would never want to reduce the fitting, and has been mentioned, it is usually enlarged to go through the roof, not reduced. My unprofessional understanding...
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    Plumber RioHyde's Avatar
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    Default

    Your inspector wasnt looking at things backwards. You cannot reduce the size of the vent. Here all vent through roof penetrations must be 3" though this varies in different parts of the country. You need to take it out the roof without reducing it in size.

  8. #8
    Forum Admin, Expert Plumber Terry's Avatar
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    Default

    It depends on how many total vents through the roof sometimes.

    Here, there needs to be a 3" area leaving the building if you have three or less toilets.

    That can be:
    2-2" vents
    1-1.5" vents

    A toilet would need the 2"
    and the shower could use a 1.5" assuming there are not other fixtures he's looking at and you have your composite somehow.

    It's the Seattle area, we don't worry about frost here.

  9. #9
    Moderator & Master Plumber hj's Avatar
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    Default vent

    Quote Originally Posted by chetwynd
    Ok, apparently what it is, it's the shower vent, and it's 2" all the way up, and then 1.5" through the roof. I think the inspector was looking at it backwards, thinking the free air coming into the system through the roof was getting reduced, when in fact it's actually getting bigger. Does this make sense? Talk to me guys...
    No. The smallest sized pipe, even if it gets larger lower down, determines the amount of air available, and if it is the one for the toilet it may have to be 2" in your area. Your area may also have a prohibition about reducing the size of a pipe before it passes through the roof. But the discussion is academic, because you have to do whatever he requires, especially if you want the remainder of the project to go smoothly.
    Last edited by hj; 01-14-2006 at 06:20 AM.

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