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Old 02-06-2011, 12:57 PM   #1
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Venting Plumbing


I have a general question about venting plumbing..

Do you have to vent the 3" ABS with the same diameter all the way to the roof?

Can you go from 3" down to 2 or 1.5" for the venting?

I've got an addition on the second story and the 3" abs takes a big zig zag to avoid being in the view of the windows. Unfortunately the bone heads that did the addition didn't seal all the joints of the vent. So condensation leaks..

If I was able to transition to 1.5" pipe, I could send it laterally through rafters which would work a lot better than the current routing.. What are the rules for transitions down from 3" pipe in the plumbing venting?


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Old 02-06-2011, 01:12 PM   #2
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this depends on a lot of factors. what is the pipe venting? where does the vent pipe go? how much of it is horizontal? what other vents do you have? where do you live? in my area, you don't have to have any certain size of vent, depending on the fixtures it serves. however, i have to upsize a vent if more than 1/3 of it is horizontal, or it runs over a certain length. also, i have to match the area of a 4" pipe with a combination of all of the vents thru the roof.


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