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Community and Q&A

Toilet stack alternatives

user-1135248 | Posted in Building Code Questions on

I’ve recently realized that air admittance valves have generally become
more permitted by code and help reduce the number of roof penetrations,
but they likely still won’t do for a sealed system [on-property septic]
as any positive pressure has to have *somewhere* to go. Thus, as far
as I know code only permits AAVs for branches but not the main stack;
there has to be *someplace* for the sewer gas and its attendant
condensation to escape. [Is that also true for systems piped into
city sewers, which would eliminate the pressure problem?]

I did some searching here, without finding much. One or two projects
sent the stack through a gable wall, which might mitigate the roof problem
but is often a pretty inconvenient way to run it, not to mention being
looked on with much skepticism on the part of the local AHJ. One of
the GBA posts seemed to imply a system based solely around an AAV, but
didn’t clarify if it was for the main stack and/or the home was connected
to city sewer instead.

So I’m just trying to clarify what’s legal, sensible, and safe to do in a
building with septic that wants to be as tight as possible and have the
least amount of stuff poking through the roof. No immediate need here,
although I recently did a bunch of noodling to design a little protective
“snow splitter” for my own stack which is about midway down a standing-seam


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  1. jackofalltrades777 | | #1

    Each area has its own code allowance on AAV's and plumbing vent stacks. In my area they allow AAV's but there must be at least ONE vent stack and that vent stack can exit through a wall. It does NOT have to exit through the roof. As long as pitch and distance from windows/doors is met, it can exit through a gable wall or any wall. In my house design I have ZERO roof penetrations. (Bathroom exhaust is handled through an ERV which has one main exhaust on the side wall and one intake on the side wall also.)

    Call your local code reivew and check with them.

  2. user-2890856 | | #2

    Termination in the open air is just that . It does not matter whether horizontal or vertical . Most model plumbing codes address this . Systems with AAVs must have at least 1 termination to the atmosphere .

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