I live in a cape cod style home, which has knee wall attics. Air from these spaces travels from the soffit vents, between the rafters, into the second floor attic space, then out the ridge vent. I am adding an addition to the home in a part of the house that does not have access to the second floor attic. Can I run the plumbing vent pipe for this new addition between the roof rafters in order to tie it in to the main vent in the second floor attic?

1 Answer 1


There might be some local code variance that prohibits it, but this is (if I understand correctly) exactly what I did and got approved.

So long as you maintain slope (so any rain that gets into the vent can run to the drain), I can't imagine why you would not be allowed to do this.

  • I agree. There's nothing different about this than running through just about any other attic space.
    – isherwood
    Mar 21, 2023 at 12:48

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