I would like to re-route some of the vent pipes in my attic so I can put down flooring for storage. currently the pipes run above the ceiling joists. what I would like to do is run the pipe below the boards until they are directly under the place in the roof that the vent pipe goes through and then go up through the roof. Also do these pipes have to be at a particular angle?

Pitch the pipe downhill to the fixture they come from,as far as a minimum I'm not aware of any ,your only draining condensation.

Please excuse my ignorance, but what exactly are these pipes for? one pipe comes from the kitchen sink and the other appears to come from the washing machine. The pipe from the kitchen sink joins with the pipe from the washing machine and from there goes horizontal for about eight feet then up and out the roof. Thanks

Suck water into a straw amd put your thumb on top......No drain......take your thumb off.......drain....Same deal ...larger scale.

Just remember that no vent shall run other than a uphill direction. Any drops or dips will allow water to sit in low spot and freeze, thus causing the piping to break.

ooohhhh, now that makes sense! thanks.

It sounds like it doesn't matter if the pipes in the attic go up and then down and then back up again. as long as there is an unobstructed path to the air outside. Does thst sound right? Thanks

thanks, but I thought these pipes were for drawing air to the fixture. do these pipes have water in them at anytime?

They have to continually rise. Condensation from moisture from sewer gases would build up and collect in the low spots,,,,with no way to drain. No plumbing inspector will pass a pipe in this fashion. You basically would be making a trap out of a vent......which will never work.

TDR, the pipes can't run up and down! They must run up towards the roof. Some codes will allow the vent pipe to run perfectly level, but otherwise up towards the roof.

This is what I needed to know. thanks to all that replied!

Wrong! The pipes can go up, sideways, up, sideways, etc., but never down.

One exception!!.........Bow vent for island sink

The person was asking about rerouting vents in the attic, not installing an island sink.

Yes and steve's point was not to run a vent in manner as not to form a trap,vents have to run UP!on an even plane

Even the yoke/sow vent has to be connected so the the low point drains.

You really don't want to change your venting system at all.You're allowed to use 45's if you run across a beam. Utherwise, you need to run it straight up. Hope this helps you out.

Can it go downhill if it then intersects another vent which pitches downhill? The drop is only a 2" street 22s worth where by one direction of the ty is a dry attic vent pitched down to another bath below and the other direction it pitches is 2" up to a 3" vertical out the roof.