Island vent alternate

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clix

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Hi everyone. I'm starting to plan out a kitchen remodel with a peninsula/island sink and have an interpretation question regarding a local plumbing ordinance (I will run everything by the inspector but want to make sure I'm not missing something obvious here). Here is what my local plumbing ordinance contains as an amendment to UPC 2009 (I've added comments where I see differences from the UPC language):

909.0 Special Venting for Island Fixtures.

Traps for island sinks and similar equipment shall be roughed in above the floor and may be vented by extending the vent as high as possible, and no lower than bottom of sink/fixture it serves [UPC 909.0 uses "drainboard height" here] and then returning it downward and connecting it to the horizontal sink drain more than five (5') feet (1524 mm) [UPC 909.0 uses "immediately"] downstream from the vertical fixture drain. The return vent shall be connected to the horizontal drain through a wye-branch fitting [UPC 909.0 also includes reference to a foot vent and connection with other vents >= 6" higher than flood level of fixtures served]. Drainage fittings shall be used on all parts of the vent and a minimum slope of one-quarter (¼") inch per foot (20.9 mm/m) back to the drain shall be maintained. [UPC 909.0 describes use of 45-90-45 for the loop construction here] Pipe sizing shall be as elsewhere required in this code with minimum size to be two (2") inch (51 mm) [UPC 909.0 has no reference to 2" minimum here]. The island sink drain, upstream of the return vent, shall serve no other fixtures. An accessible cleanout shall be installed in the vertical portion of the vent.

To me, this says:
  1. That the top of the loop should be as high as possible (up to the bottom of the countertop), but I don't have to build a two-level island to be able to accommodate the "above drainboard height" requirement (I assume drainboard means counter top, but don't see a definition anywhere)
  2. As long as I run at least 5' horizontally and use 2" PVC, I can connect the "vent" side to the drain side and do not need to tie the "vent" side into an existing vent, run a new vent to the outside or use an AAV
I've read a number of threads here and on some inspector forums regarding proper layout for an island sink vent. I have seen pictures of loops that connect in this fashion, albeit without the 5' horizontal run required, with the consensus generally being that the venting is inadequate (see: https://terrylove.com/forums/index.php?threads/proper-loop-vent.44963/ ).

So, I guess I have two questions. Is my reading accurate? If so, is there a function that the 5' run is providing to the system that the small loop vent from the thread I linked above does not provide?

Thanks in advance for any responses and for providing this resource online.
 

Cacher_Chick

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This publication ocassionally shows things that are not permitted under every code, but does ok overall.
 

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clix

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This publication ocassionally shows things that are not permitted under every code, but does ok overall.

Thanks for the response and sorry if I wasn't clear. The image you posted is, I believe, more of the standard island vent configuration and does tie the vent side of the loop into a vent to the outside. I was more curious about the alternative approach outlined by the local AHJ in my quote above where, if my reading is correct, the "vent" side of the loop only connects back to the drain.
 

clix

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Just to be clear, my reading is that the diagram attached to this reply would be permitted under the alternative approach, with the red deletions and green additions.
 

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Smooky

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Just to be clear, my reading is that the diagram attached to this reply would be permitted under the alternative approach, with the red deletions and green additions.

No, a vent is required:


....and shall, in addition, be provided with a foot vent taken off the vertical fixture vent by means of a wye branch immediately below the floor and extending to the nearest partition and then through the roof to the open air, or shall be permitted to be connected to other vents at a point not less than six (6) inches (152 mm) above the flood-level rim of the fixtures served ......
 
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clix

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The language you quote, I believe, is the standard language from the UPC. The language in the alternate approach (the amendment by the AHJ to the UPC I pasted above) does not include the language you pasted. The bracketed comments in my original post show where there are differences between the UPC and the alternative language in the amendment by the AHJ.

I understand there isn't a vent in my drawing or my reading of the amendment (but it appears to be what the AHJ amendment describes, which is why I'm confused) and that the typical setup would include a foot vent.

No, a vent is required:


....and shall, in addition, be provided with a foot vent taken off the vertical fixture vent by means of a wye branch immediately below the floor and extending to the nearest partition and then through the roof to the open air, or shall be permitted to be connected to other vents at a point not less than six (6) inches (152 mm) above the flood-level rim of the fixtures served ......
 

Smooky

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Have you got a link to the section that you are referring too? All around the country there are exceptions to the code or a completely different code. Some things are different depending on where you are located, it often changes from city to city etc. You've got to go with what the code from your area says.
 

rjbphd

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Just to be clear, my reading is that the diagram attached to this reply would be permitted under the alternative approach, with the red deletions and green additions.
This is more like the standard loop venting which used to be allowed years ago..however, I would raise the clean out higher than the p trap entry.
 

Kreemoweet

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clix said:
I understand there isn't a vent in my drawing or my reading of the amendment (but it appears to be what the AHJ amendment describes, which is why I'm confused) and that the typical setup would include a foot vent.

I don't know why you say "there isn't a vent". That amended photo you posted is exactly what your local code requires, and it IS
a vent, and unless there is also some other method your local code permits, it is not an "alternative approach", it is how you have to do it.
What is the confusion? What the unamended UPC says is irrelevant. What some folks might say on this or that internet forum is
also irrelevant. If someone, somewhere, posts some actual empirical performance data regarding various venting designs, then that
might be of some interest. But it would be of theoretical interest only.
 

clix

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Confusion was merely because of inexperience and trying to understand how this approach provides an adequate vent for the system. It doesn't seem that this provides the same type of access to air that the UPC island vent layout so I wanted to make sure the way I was reading the language was correct, again, given my limited familiarity. This alternative is great for my purposes, so not trying to argue against it, just wanted a sanity check.

I don't know why you say "there isn't a vent". That amended photo you posted is exactly what your local code requires, and it IS
a vent, and unless there is also some other method your local code permits, it is not an "alternative approach", it is how you have to do it.
What is the confusion? What the unamended UPC says is irrelevant. What some folks might say on this or that internet forum is
also irrelevant. If someone, somewhere, posts some actual empirical performance data regarding various venting designs, then that
might be of some interest. But it would be of theoretical interest only.
 

Cacher_Chick

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So, for the guys that are plumbing under UPC, are you telling us that you can have a loop under the cabinet with no vent connection downstream? I have trouble believing that that trap would not siphon if one drained a sink basin full of water.
 

clix

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While I am also curious about your question regarding function, my question was about an amendment in one jurisdiction.

So, for the guys that are plumbing under UPC, are you telling us that you can have a loop under the cabinet with no vent connection downstream? I have trouble believing that that trap would not siphon if one drained a sink basin full of water.
 

Smooky

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CITY OF SAINT LOUIS

909.0 Special Venting for Island Fixtures. Traps for island sinks and similar equipment shall be roughed in above the floor and may be vented by extending the vent as high as possible, and no lower than bottom of sink/fixture it serves and then returning it downward and connecting it to the horizontal sink drain more than five (5) feet (1524 mm) downstream from the vertical fixture drain. The return vent shall be connected to the horizontal drain through a wye branch fitting. Drainage fittings shall be used on all parts of the vent and a minimum slope of one quarter (1/4) inch per foot (20.9 mm/m) back to the drain shall be maintained. The return bend used under the drainboard shall be a one (1) piece fitting or an assembly of a forty five (45) degree (0.79 rad), a ninety (90) degree (1.6 rad) and a forty five (45) degree (0.79 rad) elbow in the order named. Pipe sizing shall be as elsewhere required in this Code with minimum size to be two (2) inch (51 mm). The island sink drain, upstream of the return vent, shall serve no other fixtures. An accessible cleanout shall be installed


https://www.stlouis-mo.gov/internal-apps/legislative/upload/Ordinances/BOAPdf/66615x00.pdf
 

Cacher_Chick

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Just seem like AAV is SOOO much easier...than all that piping...

It's a bit like using a backwater valve to prevent sewage from backing up into the house- it should work but it also may fail at a most inopportune time. When the piping is all installed properly in the first place, there are no mechanical components to fail, and the system will work properly throughout its intended lifespan.
 
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