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a4aj 01-31-2010 05:47 PM

Combining vent pipes in the attic.
Can I combine multiple vent pipes into a single vent pipe in the attic?

I am in the process of installing a metal roof. Currently there are 5 vent pipes exiting through the roof (1.5 to 2 inch pipes) and I would like to combine the pipes into a single large pipe that will exit through the roof. Don't want multiple pipes exiting through the new roof due to possibility of leaking and aesthetics.

In the attic, I have clear access to all of the pipes and they are evenly spaced about 5-6 feet apart. Is there a problem with running a horizontal pipes to combine them? All of the horizontal pipes will be minimum 8 feet above the highest plumbing fixture.

Thank you for your help.


Scuba_Dave 01-31-2010 06:22 PM

What is the purpose of each vent pipe ?

a4aj 01-31-2010 07:56 PM

5 vent pipes are for 2 sinks, 2 showers, 2 toilets, and 2 laundry drains. About 2 plumbing fixtures to each vent pipe.

Thanks for your help.


md2lgyk 02-01-2010 10:05 AM

I think it depends on the applicable code where you live. What you'd like to do is legal under the IRC, and in fact the log house I'm currently building is plumbed that way. It has only one roof penetration - the main stack. I don't think it would be legal under the UPC.

rudolph58 02-01-2010 10:12 AM

as long as you keep a proper slope to wash each vent from the new main vent,i see no problem.use 4" to penetrate the roof and to tie all the vents together.

AppleMac*Fit 02-04-2010 11:20 AM

I wanted to do this before we had our metal roof installed, but didn't. :( I kind of regret it. The only roof penetration on the front of our house is a plumbing one, so if we would have combined vents we could have had zero roof penetrations on the front of the house. Definitely combine them if code allows! :yes:

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