In article EEGmh.1750$IT2.561@trnddc06, says...
Just out of curiosity.....I'm wondering why these sink vents need to go
through the roof instead of the side of the building (like gable end of
attic)?

Some jurisdictions allow side venting, others don't. Concerns include
where vapors go that come up from the sewer -- some idiot pours gas down
a drain, the fumes come up your vent stack, do they dissipate outdoors
or accumulate in your attic?

--
is Joshua Putnam
http://www.phred.org/~josh/
Braze your own bicycle frames. See
http://www.phred.org/~josh/build/build.html