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Community and Q&A

Best practices for dealing with DWV line penetrations

Mark_Nagel | Posted in Green Building Techniques on

I’m curious as to what approach people take with regard to routing Drain Waste Vent lines out of the conditioned space.

My design (zone 4c, so no icing issues) is a ranch (on slab) with an unconditioned attic (cold roof).  I’ll have a dropped ceiling, but it’ll only be a 3 1/2″ drop (2x4s).

Although I have things fairly well clustered in the overall floor plan, the layouts of the fixtures within each bathroom tend to raise concerns over how to manage the various vent lines.

In a perfect world I’d be tying all of the DWV lines together before punching through the ceiling’s sealing layer (and into the attic space), but I’ve got water fixtures slated to go on different sides of the rooms.  So…

Is it just something that folks accept (and really isn’t talked about much), or are there some tricks/tips to go by?

I am not thinking I’m going to want to try and cutting a bunch of wall studs in order to achieve horizontal distance (horizontal as in lateral, not as in level).  My dropped ceiling which would provide for horizontal/lateral travel won’t really do anything for routing such pipes (due to it only proving for a headspace of 3 1/2″ space; not much room left to add in slope for the DMV piping).  Pretty much appears that I have little choice than to punch straight up and through wall top plates and through the vapor barrier and insulation (and then tie together into the main stack).

Just curious as to what folks do (because I’m not seeing much talk of it).

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  1. Expert Member
    BILL WICHERS | | #1

    What I've done in the past is to seal around the vent pipe pentration in the attic floor using canned foam, then go through the roof with the usual weather boot. Nothing fancy.

    All you need to do is seal up your building envelope, so if you have an unconditioned attic, that typically means the attic floor is what you need to air seal. The roof penetration doesn't really matter for air sealing in this case, it just needs to be weather sealed (rain tight).


  2. Mark_Nagel | | #2

    Thanks, Bill.

    I just need to be a little less anal. I aim for the optimal and then back off as needed. I'll just punch up as needed.

    1. Expert Member
      BILL WICHERS | | #3

      Perfect is the enemy of good :-)


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