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Thread: Frozen Soil Stack Vent

  1. #1
    DIY Junior Member jasper1372's Avatar
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    Default Frozen Soil Stack Vent

    We've built two new homes in the past 14 years and both of them have had the same problem with the soil stack (plumbing vent) freezing when the temps get way under zero for a number of days in a row.....you know, a 20 or 25 below kind of thing.

    Our soil stack is 3" white PVC Pipe and sticks through the roof about 14 or 16 or so".

    Is there something that us is very cold climates could be doing to solve this problem ? Quite a number of our neighbors have this problem too.

    I bought this insulating hood last fall that fits on the stack where it comes out of the roof....but I swear it made things worse than last year. The only thing I can think of is to wrap the exposed pipe in heat tape next fall and hang a cord over the side of the roof and plug it in when the temps get way under zero which is when we have our problem....won't that look nice

    Any suggestions ????
    Last edited by jasper1372; 03-08-2009 at 08:01 AM.

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default vent

    That is the reason most codes require that the roof penetration pipe be 1" larger than the vent pipe, and a 4" pipe the minimum size, starting 1' below the roof. The lead flashings that surround the pipe also help direct warmer air up around the pipe.

  3. #3
    Illinois Licensed Plumber SewerRatz's Avatar
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    Default

    Here in Illinois they make us increase the vent one pipe size larger in the attic 12" below the roof, to prevent frosting over of the vent pipe. So in your case it would be increased to 4 inches.


  4. #4
    DIY Junior Member jasper1372's Avatar
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    Quote Originally Posted by hj View Post
    That is the reason most codes require that the roof penetration pipe be 1" larger than the vent pipe, and a 4" pipe the minimum size, starting 1' below the roof. The lead flashings that surround the pipe also help direct warmer air up around the pipe.
    It is currently one inch larger. The plumbing vening inside the house is 2" PVC pipe and up in the attic it goes to the 3" as I mentioned.

    So it sounds like in our case our plumber should have maybe used 3" venting through the housing envelope and then gone to 4" up in the attic and through the roof ?

    I am obviously wanting to fix this problem in our current home by whatever reasonable means possible....but in the next house the plumber is going to wonder why I'm so obscessed with knowing his venting procedures and knowledge....lol. I've had this problem in two new homes and as the saying goes: First time shame on you (plumber), second time shame on me (for letting them do this to me twice)....the third time I think I'll just jump off a cliff or something :-)
    Last edited by jasper1372; 03-08-2009 at 09:00 AM.

  5. #5
    Illinois Licensed Plumber SewerRatz's Avatar
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    This is from an old old plumbing code book. Which makes makes some sense.

    No pipe of any building should open to the air with less than a 4-inch end. Small pipes should be increased to 4 inches before passing through the roof, as shown in Fig. 148. Pipe 4-inch and larger, up to 6-inch, should be increased to 6-inch. The object in all cases being to prevent closure by hoar frost. With 6-inch and larger pipe, it is doubtful if it is ever necessary to increase the size at the roof, excepting in buildings with cold roof space, no matter how high the building may be; yet some city ordinances call for an increase of one size regardless of size, which is manifestly foolish, as it permits increasing 2-inch to 2 1/2 or 3-inch on any type of job, and this is known to be inadequate in any but southerly latitudes.

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