Attaching New Attic Vents to Existing Attic Stack Vent


Old 02-10-09, 08:38 AM
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Attaching New Attic Vents to Existing Attic Stack Vent

We added a whole new bathroom and now have (2) 2” vents pipes and (1) 1.5" vent pipe going into the attic. They range in distance of 13' to 20' away from an existing 4” cast pipe exiting the roof. This cast stack already has two other cast vents tapping into it: 1.5" (no longer used - YAY!) and another 1.5" or a 2” (not sure).
I could run the new 1.5" vent to the unused 1.5" stack tap, but it's about 20' away. Seem ok? But, what about the other (2) 2” vent pipes? I cannot find anything about rules for combining vent pipes, but can I hook them together and run just one 2" pipe to the stack? Heck, could I connect the 1.5" to the 2" pipe? And then how should I connect them to the stack? There might be room to cut the big stack and insert a new 4"-2”-4" tee, but that’s a PITA. Any ideas about running/combining these vent pipes or hooking them into the big ole monster pipe?
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Old 02-10-09, 01:47 PM
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Vent Pipes

karen_z: You can tie all three vents into one 2in. line. If thats a 2in connection on the stack thats the place to tie in.

If you have to cut into the cast iron you're right [PITA].

1: You have to suport the upper part of the stack that goes thru thu the roof so it dosen't fall out.
2: If you have a 4 1/2in grinder you can cut the iron using cut-off discs; it has to be cut reasonably straight with about 1/4in. play.
3: You need a 4x4x2 tee [the last dia. is always the center], your best bet is to get this fitting in no-hub and adapt to pvc on the branch. You will need 2 Fernco or Mission couplings; check the markings on the cast iron, should be xh or sv, you need this info to get the right coupling.

FYI vent fittings are installed upside down, the flow of the branch should be heading toward the roof, hope this helps,luck.
Old 02-10-09, 02:07 PM
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combining the vents may be ok. it all depends on what is connected to them. vents have a dfu range just like the drain. there is no problem with tieing them into the main vent as long as you have enough room for the pitch.

may i suggest one of these KOZY KOLLAR ROOF FLASHING they can be installed without even getting on the roof
Old 02-11-09, 07:57 AM
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That's all great news and answers my questions. Thanks!!

And, I love that Kozy Kollar.


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