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» ICC Bulletin Board » Code Chat » Plumbing, Mechanical and Fuel Gas Codes » 1601.4 Under-floor plenums.

   
Author Topic: 1601.4 Under-floor plenums.
Casey
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1601.4 Under-floor plenums states that "An under-floor space used as a supply plenum shall conform to the requirements of this section. Fuel gas lines and plumbing waste cleanouts shall not be located within the space."

What about a supply plenum between a dropped celiing and the ceiling above? Can I have gas lines in that plenum?

In this instance, the plenum is in the ceiling of a corridor on 4 floors of a condo building. It is used to supply make-up/outdoor air to each unit from a duct from the roof unit. The floor/ceilding assembly between each floor is rated and we have a dropped ceiling per above. We want to run the gas trunk line in that same plenum space to each unit.

Let me know what you all think and thanks.

Posts: 11 | From: Salt Lake City, Utah | Registered: Sep 2006  |  IP: Logged
Builder bob
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Look at the definition of a concealed space in International Fuel Gas Code. I believe you will see the light.

CONCEALED LOCATION. A location that cannot be
accessed without damaging permanent parts of the building structure or finish surface. Spaces above, below or behind readily removable panels or doors shall not be considered as concealed.

[ 07-31-2009, 06:11 AM: Message edited by: Builder bob ]

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Posts: 4199 | From: Lost in the South........ | Registered: Apr 2004  |  IP: Logged
mueller
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Casey-
Is this a 4 story building.If so the IRC section you metioned does not apply. Must use IBC.Also see IMC sec. 601.2.1,this sets some conditions for using this space for a plenum.Also see IFGC 404.1 prohibited locations.

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Builder bob
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Me thinks that the plenum space he is talking about is not a true plenum as the code describes. I am sure that the HVAC systems are using ducted runs fo supply and returns, therefore this space isn't a plenum.

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Posts: 4199 | From: Lost in the South........ | Registered: Apr 2004  |  IP: Logged
Dr. J
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A couple of issues:

For the purpose of this post, I will assume Casey is accurate in his description of a plenum - the duct from the rooftop unit just stubs out of the shaft and feeds the space between the floor and ceiling, with transfer openings to each unit. If BB is right about the air really being ducted, then not much of an issue - just don't run the pipe in the duct.

I do not see any issue with IFGC Section 404. The space is a plenum, not a duct, and yes there is a difference. If the code meant plenum, it would have said plenum.

However, if this is new construction, and the plenum is new, it is in violation of IBC 1017.4 which allows the above ceiling space in a corridor to be used as a plenum, but only a return plenum. If not new, adding gas piping may open the door for the AHJ to require the outside/makeup air to be ducted.

Posts: 516 | From: Colorado (Denver area) | Registered: Mar 2005  |  IP: Logged
Casey
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While the other option we are looking at is to duct the make-up/outside air to the units thorugh th ecorridors, my question is what Dr. J outlined and I am using the space as a supply plenum. It would not be a concealed space as we are using a lay-in ceiling with easily removable panels.

My reading of IMC 601.2.1 Corridor Ceiling allows my use of the plenum space I desribed by meeting the one #4 comment.

I agree that IFGC 404 doesn't cause any issues in regard to my application.

Dr. J's last comment regarding 1017.4.1 is correct in that it references return air plenum only. However, my local code official has allowed make-up/outside air supply plenum in the past.

Having said all that, now that we are seeing the costs for plenum rated wiring, etc. it is actually a little more expensive to do the plenum vs. a ducted system so we are doing the duct. Thanks for help.

Posts: 11 | From: Salt Lake City, Utah | Registered: Sep 2006  |  IP: Logged
Dr. J
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You have made a wise choice young Padawan. Plenum rated wiring was probably the least of the cost issues.

If all those openings were transfer openings, they would have required smoke/fire dampers (unless the AHJ makes stuff up about that also). As ducted openings you probably would meet the exceptions in 716.5.4 and no dampers would be needed.

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Lexington Park
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Are you citing the right code (1601.4) 4 story condo's are these 4 story townhouses or stack units above each other? Residential code only applys one & two family dwellings and townhouses.
My concerns would be if gypsum boards is being used and outside air that might be below dewpoint
according to 602.2 IMC

Posts: 8 | From: Troy, MIchigan | Registered: Apr 2006  |  IP: Logged
   

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