# P3112 Island Fixture Venting



## TimNY (Jun 17, 2011)

Looked at one of these venting a lav.  Well, it's kind of like this except the vent down from the lav connects to the fixture drain from the tub, rather than downstream from the lav drain connection. Anyway, while trying to figure out the confused plumbing, I came across this from the icc: 
	

		
			
		

		
	

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 WHere is the wording in the code that requires the dry vent from the island vent to the vertical stack?  Is it required? Thanks,Tim

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## mark handler (Jun 17, 2011)

Here are two easy solutions


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## jar546 (Jun 17, 2011)

The aav cannot be used because it has to be 6" above the flood rim unlike what is shown in the photo.


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## mark handler (Jun 17, 2011)

jar546 said:
			
		

> The aav cannot be used because it has to be 6" above the flood rim unlike what is shown in the photo.


Check with your local codes to find out if they are legal for use in your area. And there is alternate means and methods...


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## TimNY (Jun 17, 2011)

In Mark's photo you again see the connection to the stack from the vent down from the sink.. But I don't see the wording that requires that.

I think AAV has to be 4" above the fixture arm connection, not the flood rim (I think it used to be 6" above the flood rim a code cycle or two ago)

Told him he had to provide a cleanout above the flood rim of the sink.. which is going to require an access panel.. at which point he could have used an AAV.. Doesn't really matter to me, but the plumbing below the floor is also in question.


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## Francis Vineyard (Jun 18, 2011)

Assuming a bathroom because of the tub drain connection; I’ve yet to see an island lavatory in a residential unit. Other than in commercial repair facilities with multi-station hand washing sink; island fixtures are customarily in kitchens. 

P3112.1 Restricts this venting method to the island sinks and lavatories. If this is indeed an island fixture then the vent installation to the tub drain should not be possible or permitted upstream against the direction of flow.

P3112.2 This is the “foot vent” where the vent after it reaches above the drainage outlet (as opposed to the flood level rim) will eventually have to connect to the “outside vent terminal” above the highest fixture.

P3112.3 The lowest point of this vent sloped and connected in accordance Chapter 30; Sanitary Drainage shall connect to the drainage system accordingly being that this horizontal vent will need to drain as such. And because of the potential of this vent becoming clogged owing to the fact that it is a vent (not a drain that normally gets flush clear) below the flood level rim it needs to have an accessible cleanout on the vent side for “all vent piping located below the flood level rim of the fixtures.”

Question; is “highest fixture” another way of saying the highest flood level rim?


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## TimNY (Jun 18, 2011)

Thanks, Francis.. P3112.2 had me confused:

"The vent or branch vent for multiple island fixture vents shall extend to a minimum of 6 inches (152 mm) above the highest island fixture being vented before connecting to the outside vent terminal."

I took is as "The vent/branch vent for multiple island fixtures..."

But what it means is, "the vent (or the branch vent, in the case of multiple fixtures), shall extend to a minimum..."

Just something I never deal with.. usually see AAVs.  Probably better off, as it now seems this island vent isn't even close to compliant.

Lacking any better direction, I would say "highest fixture" means "flood rim of highest fixture", that way there is no chance of the backed up sink/lav clogging the "outside vent terminal"


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## Francis Vineyard (Jun 18, 2011)

Here's a different variation where it may not connect above the fixture but still works and is similar to mark h picture above IMO.

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## TimNY (Jun 18, 2011)

Yeah that one is a bit easier to understand.


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## Francis Vineyard (Jun 19, 2011)

Could use some help in how the code addresses island fixtures to be wet vented. See this method frequently in older homes.

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## TimNY (Jun 19, 2011)

I would say that as far as the IRC is concerned, the vent does not connect above the flood rim.

I do note that those diagrams indicate a 3" drain and vent (wow!) for the sink.  Possibly an older method; maybe permissible under UPC?

Reminds me of another method I heard of..  Where the stack is 8" and there are no individual vents.


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## Francis Vineyard (Jun 19, 2011)

Tim, my understanding is for the most part a 3" horizontal will have an air space above the fluid discharge.  There are allowances for bathroom and kitchen fixtures; see appendix N.  I imagine given the low amount of dfu's the distance could be up to 100 ft. limited to the clean outs.


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## jar546 (Jun 20, 2011)

So where are we on this one?

I am looking through the IPC (yes I know this is an IRC issue) to see if the language is similar for AAV's.



> 917.4 Location. Individual and branch-type air admittancevalves shall be located a minimum of 4 inches (102 mm) above
> 
> the horizontal branch drain or fixture drain being vented.
> 
> ...


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## jar546 (Jun 20, 2011)

There is not doubt that the photo of the AAV above is not compliant since it is neither 4" above the fixture or 6" above the flood rim.

What I would like to know is what is the actual requirement for that kitchen sink?

Can it be (AAV) 4" above the fixture drain and be compliant or does it have to be 6" above the flood rim?

I am confused by the language in that section.


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## Francis Vineyard (Jun 20, 2011)

jar546 said:
			
		

> There is not doubt that the photo of the AAV above is not compliant since it is neither 4" above the fixture or 6" above the flood rim.
> 
> 
> 
> ...


 I am confused by the language in that section.



> 917.4 Location. Individual and branch-type air admittance valves shall be located a minimum of 4 inches (102 mm) above the horizontal branch drain or fixture drain being vented. The air admittance valve shall be located within the maximum developed length permitted for the vent.


 The _fixture drain_ is the horizontal pipe between the trap to the vent; 906.1 & 912.2.4 The confusion may be the difference is a fixture outlet is above the fixture drain and branch drain.

The commentary notes that the air admittance valve need not extend above the flood level rim of the fixture served because in the event of a drain blockage, such device will trap air between it and the rising waste, thereby protecting the device from contamination.



> Stack-type air admittance valves shall be located not less than 6 inches (152 mm) above the flood level rim of the highest fixture being vented.


 910.3 adding an AAV to a compliant configuration. Vent stacks as defined start 6" above the highest fixture flood level rim.

I believe confusion is explaining the difference of ground, grounded and grounding to a plumber as this is to an electrical expert.


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## TimNY (Jun 20, 2011)

That's why I always use the term "fixture arm" in relation to the AAV.. When you say "fixture drain" people just get confused.


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## JBI (Jun 20, 2011)

Sounds like there's some confusion on 'individual' vs 'stack' type AAVs.


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## Francis Vineyard (Jun 20, 2011)

JBI said:
			
		

> Sounds like there's some confusion on 'individual' vs 'stack' type AAVs.


That's it JBI; Stack!

It would IMO be a very large home; note AAV is limited to six branch intervals in IPC 917.3.3 that's not in my version of the IRC.

http://www.studor.com/vent_compare.htm


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## jar546 (Jun 21, 2011)

That clarifies it, meaning you can have an AAV under a sink providing it extends up 4" above the fixture drain (aka horizontal pipe to the vent/aav) which must be at or above the weir of the trap anyway.  Therefore it can be below the bottom of the sink if the trap is set lower.


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## jar546 (Jun 21, 2011)

That makes this installation compliant with the 4" rule since we are talking about the fixture drain and not the actual drain inside the sink.


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