Horizontal Island Loop Vent?

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Jer805

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Does an island loop vent have to come to a point (45-90-45 bends), or can the top run horizontally for a few feet using two 90 bends and no 45s? I would like to run my island sink drain pipe down one leg of the island and the vent pipe down the adjacent island leg a few feet away. Thoughts?

Other crazy options if the horizontal approach is not allowed... The skirting around the top of the island could conceal a traditional island vent (two 45 & 90 bends) then vertical for 7" and a horizontal run to the leg. Or, one 45, a 90, and a diagonal pipe but I'm still left with a short horizontal section before reaching the leg. Or, can the trap arm connect to a horizontal drain pipe which runs to the drain leg? Thoughts?

By the way, this is a permitted job so it will be inspected.

Thanks for your help!

Based on John's response, would the layout in the below diagram be allowed?
 

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John Gayewski

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I removed a section of horizontally vented piping under a cabinet one time. It was copper pipe. It was completely packed full of the most god awful sludge you could imagine.
 

Tuttles Revenge

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I removed a section of horizontally vented piping under a cabinet one time. It was copper pipe. It was completely packed full of the most god awful sludge you could imagine.
I was all set to say that I never could figure out why that configuration of 45-90-45 was always required... guess that answers that..

technically the pitched pipes are horizontal since they're at a 45... But also vertical. So ultimately the answer is yes.. but no.

island_sink_bert_polk.jpg
 

Jer805

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No horizontals on an island vent.
Hi John, I was afraid of that. Still searching for a solution... At what point can the vent run horizontally? Or, can a trap arm enter a sloped (but by definition vertical) drain pipe? Other than an AAV I can't believe this problem hasn't been solved before. Thanks!
 

Jer805

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I removed a section of horizontally vented piping under a cabinet one time. It was copper pipe. It was completely packed full of the most god awful sludge you could imagine.
That doesn't surprise me. In this case a sloped drain seems better than a horizontal vent.
 

John Gayewski

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Hi John, I was afraid of that. Still searching for a solution... At what point can the vent run horizontally? Or, can a trap arm enter a sloped (but by definition vertical) drain pipe? Other than an AAV I can't believe this problem hasn't been solved before. Thanks!
A vent can run horizontally (less than 45 degrees) at 6 inches above the flood rim of fixture it serves.
 

wwhitney

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Still searching for a solution...
You may have to go figure out how to run both the loop vent and the drain in/near the same leg.

How about a plan view of the island, along with where you'd prefer to penetrate the subfloor and where the drain and vent will run to under the floor?

Cheers, Wayne
 

Jer805

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I was all set to say that I never could figure out why that configuration of 45-90-45 was always required... guess that answers that..

technically the pitched pipes are horizontal since they're at a 45... But also vertical. So ultimately the answer is yes.. but no.

island_sink_bert_polk.jpg
Thanks! I know this layout well. Now the question is, does the code restrict the length of the two diagonal pipes between the 90 bend at the top and the two 45s? If not, then I'll cut them to aprx 11 inches in length so that the space between the drain and the vent is enough to fit down my island legs (see my pic). My understanding of the code is 45 or steeper is considered a vertical pipe. Thoughts? Thanks!
 

wwhitney

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Thanks! I know this layout well. Now the question is, does the code restrict the length of the two diagonal pipes between the 90 bend at the top and the two 45s? If not, then I'll cut them to aprx 11 inches in length so that the space between the drain and the vent is enough to fit down my island legs (see my pic).
Easier if you attach a pic to your latest post, rather than edit the first post and use a PDF.

Fundamentally, sure you can do that. But you should draw in what is happening below the floor to be sure you those details will still work with the wider spread between the vent loop legs. Plus you'll almost certainly need your trap arm lower for your sink, and even if not, the highest you could get it would be with a street 45 into a san-tee. And you'll need a cleanout fitting on the vent leg of the loop.

Cheers, Wayne
 

Jer805

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Easier if you attach a pic to your latest post, rather than edit the first post and use a PDF.

Fundamentally, sure you can do that. But you should draw in what is happening below the floor to be sure you those details will still work with the wider spread between the vent loop legs. Plus you'll almost certainly need your trap arm lower for your sink, and even if not, the highest you could get it would be with a street 45 into a san-tee. And you'll need a cleanout fitting on the vent leg of the loop.

Cheers, Wayne
Thanks Wayne, I'll take your posting advice to heart next time. You're right on the plumbing details. Now that I'm at least in the ballpark (drain and vent relative to island leg), I'll mock up and fold in the details like the cleanout. I think the details below the floor will workout okay given the wider loop vent. Thanks again!
 
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