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The vent in this house is 3", however, it has a 45* jog that starts about 2' from the attic floor, then extends at angle for maybe 4', then returns vertical. It extends past the roof maybe 18" and that's pretty close to the roof peak. Don't see why it was set at an angle. It suspect icing maybe at most four times in the six years we've been here. The attic is insulated (maybe 3" in most of the area), but is also full of air leaks. What could be some reasons for having it at an angle, and could that be why it's icing?
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No doubt your plumber thought it was easier to offset the pipe to a point where he/she could cut the hole through the roof from a kneeling position rather than lay on their back where the pipe would have been straight.
Technically speaking what you have is a vertical offset, because in plumbing any line which rises at an angle from 45 to 90 degrees above horizontal is considered a vertical pipe.
They could have used a pair of quarter bends and run the offset flat across the trusses before turning upwards again because code allows a horizontal offset in a vent line once the line reaches a point at least 6" higher than the flood level rim of the highest fixture served by that vent.
Having said all that, you are also correct about the ice closure. By running your vent with that offset instead of going straight up through the roof they added another 7' or 8' feet of pipe that is exposed to the cold. -
Offset vent
Thanks, LayzPup.Comment
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