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Community and Q&A

Minimizing roof penetrations

DigitalBenny | Posted in Green Building Techniques on

What do you think about a Chicago Loop drain vent being applied to the whole DVW system of a slab on grade house to eliminate roof penetration? In other words, the vent pipe would go DOWN into the slab before coming UP outside the envelope? Similar to a kitchen island fixture vent, but applied to the entire plumbing system. Trying to figure out how to avoid both a vent pipe through the roof and the use of AAV’s…

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  1. Akos | | #1

    I'm pretty sure the inspector will have issues with that one.

    Drain vents are pretty easy to seal up, there are much larger sources of potential air leaks in a house build to worry about.

    Nothing wrong with the occasional AAV, but your house still needs at least one positive pressure vent, no easy way around a roof vent.

  2. Malcolm Taylor | | #2


    You won't get away with a Chicago Loop for the whole house - a whole house one wouldn't work anyway, individual fixtures would still have their traps drain - so if you don't want any vent stacks you are stuck with AAVs (unless you are in Canada). I agree with Ako: I wouldn't be comfortable without some way to relieve pressure and vent sewer gas, but I think codes in the States do allow whole house AAV venting.

    Why the aversion to a vent stack penetrating the roof? Any decent builder should be able to guarantee it won't leak.

  3. DigitalBenny | | #3

    Thanks Akos and Malcolm for your replies. Maybe I didn't use the right terminology or omitted proper explanation of my idea.
    There would be a positive pressure vent. All traps would still be vented. The only difference is the "stack" would go into the floor and exit outside the house envelope. For instance, a vertical pipe on the outside of the wall that extends to the roofline. Within the house, the vents would all go upward to the required heights relative to the drains they serve. It's not that I don't want a stack, I just don't want it to penetrate the roof. Does that make sense?

    1. Malcolm Taylor | | #4

      Ah okay - so not a Chicago loop at all - you just want to send the vent stack horizontally outside the envelope and run it up the exterior.

      Under most codes this pipe, whether inside or out, would have to terminate above the roofline. Under the codes that do allow it to terminate elsewhere - on a gable wall for instance - there are a number of setbacks that need to be observed to things like operable windows and roof vents, which make it quite difficult.

      It's a lot of gymnastics to avoid what really isn't a problem.

  4. DigitalBenny | | #5

    You're *kinda* getting my point... I want to send the vent stack down, through the slab, THEN horizontal beyond the footing, then vertical along the exterior wall. The vent would still be terminating above the roofline, but would not penetrate the envelope except for the slab.

    1. Malcolm Taylor | | #7

      Okay - leaving all my code and practical reservations aside - the only way you could do that is by connecting the lowest horizontal level of the vent that passes under the slab with the main 4" sewer pipe so the it would not fill with condensate.

      Conceptually it strikes me as being similar to some 0ne suggesting entering their house through a tunnel leading to a hatch in their crawlspace to avoid having to periodically lubricate their door locks.

  5. User avatar
    Peter Engle | | #6

    Most codes/inspectors would not allow it. The pipe will generate a LOT of condensation, and that must be drained by connecting it to the sewer main. This will make the lower portion of the loop subject to clogging. Also, the stack is not permitted to run up the outside of the house in cold climates, as the steam/moisture in the pipe tends to freeze inside the pipe and plug it up.

    From the 2015 IRC:

    P3102.1 Required vent extension. The vent system serving
    each building drain shall have not less than one vent pipe that
    extends to the outdoors.
    P3102.2 Installation. The required vent shall be a dry vent
    that connects to the building drain or an extension of a drain
    that connects to the building drain. Such vent shall not be an
    island fixture vent as permitted by Section P3112.

    Section P3112 is the section that allows a "Chicago Loop" style drain for island sinks. So, your idea is specifically prohibited under the I-codes series.

  6. User avatar
    Jon R | | #8

    As others say, it would form a trap in the vent and IMO be a violation of this: "Vent and branch vent pipes shall be graded, connected and supported to allow moisture and condensate to drain back to the soil or waste pipe by gravity."

    I believe that the vent can leave through a wall (it may need to be insulated). I suppose that in some theoretical sense, an envelope hole near the neutral pressure plane is superior to one higher up.

  7. Gary_M | | #9

    I also have the aversion to the roof penetration however my thought was that I would run the vent into a framed "chimney chase" that will also be used for a triple wall stove pipe and vent both out thru the top (not thru the roof). I still need to confirm this with my plumbing inspector, but I don't think there is an issue as long as I maintain proper clearances. I would rather have a the pipe enclosed in a box that looks like masonry chimney form a ascetics point of view then a pipe running up the side of my house as well. This would also make it possible I can run the vent out high / not under the footing.

  8. Joel Cheely | | #10

    A vent doesn't have to go through the roof. It can go through a sidewall with some limitations. Allowed in 2015 IRC P3103.

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