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We're taking down a section of the wall between our kitchen and living room and we want to drop the 'bar height' down level with the sink. Unfortunately, the bulk of the section we're removing has plumbing and electrical in it. Most of that is not an issue. However, I'm trying to determine if I can reroute the air vent for the plumbing as below. The closest I could find on how to do it would be with an 'island loop': enter image description here I'm trying to determine if I can reroute the vent as such, rerouting in blue, existing sink level in red line: enter image description here

As far as I can tell, the relevant bit of the georgia plumbing code is this, but does this mean the top of the loop has to go 6" above the sink?: enter image description here

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In this case, it doesn't look like you need the vent loop at all, and the 6" height requirement is well-covered by the vent stack going clear up to the roof.

If you want to put that loop in, it definitely isn't going to hurt anything. It just doesn't look like you need it.

You could branch off the vent stack above the junction and use a flatter slope to get the pipe over to the point where you take it vertical. The slope you show is steeper than you strictly need it to be.

The important thing with a plumbing vent is that there is an air break downstream from the p-trap to prevent water pressure from siphoning the trap dry, and to prevent sewer gases under pressure from bubbling up through the water in the trap into your living area.

You can just put an up-turned wye coupling in the existing vent stack just above the existing connections, run it through the same path you show in your diagram, and tie back in with a 90° elbow (or a couple of 45° elbows), and cap off that 2" pipe in the wall straight above the connections to the big drain pipe.

Vent loops are for situations like kitchen islands, where there is no air break vent path without using a little ingenuity to create one

  • Ok, that makes sense. I guess I just thought going that big route did need a 'little ingenuity'. Why a wye coupling and not a 90 degree T if I need a gentle slope? – rfusca Aug 16 '15 at 23:20
  • @rfusca They make 90 deg wye connectors. But I might look for a 22.5 or even use a couple of 45's (rotate them to get the angle you want), making it easier for any water that might splash up into that stretch of pipe to drain back out smoothly. A wye also has a gentler sweep instead of hard angles, which can make snaking a little easier if that's ever an issue. You definitely need that to slope up, just not as steep as your diagram shows. – Craig Aug 16 '15 at 23:40
  • Awesome, thanks. Ya, my slope was more dramatic simply to show that I know I needed a slope. I looked up the actual requirement of N inches of raise per X number of feet (just don't remember off the top of my head). – rfusca Aug 16 '15 at 23:42
  • The most important slope related to the vent is between the p-trap and the vent, so that there is always an air gap at the top of the pipe (if the pipe's full of water, then water pressure can siphon the trap dry). For dry vent pipe I think the requirement is about 1/4" per foot, which means you're only required to have that pipe rise a few inches. Appropriate slope for a wet drain is pretty important, too, to maintain fast enough water flow so that solids don't stop moving. ;-) – Craig Aug 16 '15 at 23:48

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