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Shaft Wall Rating in Individual Residential Units

R

rosegamble

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Jul 9, 2021
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South Carolina
Hello All,

Working with a R-2 building. These are two-story individual residential units. If a shaft containing mechanical ducts is running exclusively through a unit without sharing a shaft wall or branching into another residential unit, does it have to be rated like a traditional shaft wall? I see 713.1.2 in the 2021 BC (the applicable code) but this is for "unconcealed" openings and my commentary indicates this does not apply to ductwork with walls around them.

Thanks!
 
Is the floor/ceiling assembly rated? If not, nothing needed (2021 IMC 607.6.3) If they are, a fire damper listed for the assembly type is needed, no shaft needed (IMC 607.6.1). Not 100% sure of the corresponding IBC sections but pretty sure its in section 717 of the IBC.
 
Hello! It is unrated. But that’s the exact issue — I cannot find this in the IBC anywhere except 713.1.2 in the 2021 BC (and key word there is unconcealed).
 
rosegamble said:
Hello! It is unrated. But that’s the exact issue — I cannot find this in the IBC anywhere except 713.1.2 in the 2021 BC (and key word there is unconcealed).
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You're reading the code backwards. You don't start in shafts, you only need a shaft if some other part of the code sends you there to get the specifics about shafts. If you start in the right place, 717.1.2.1, you will probably find that there are no requirements other than filling the annular space with something like fiberglass or mineral wool insulation (717.6.3).
 
Ducts would go from an attic (where the units are) to service the second floor and first floor. No basement in this scenario but if that changes something would be interested to know. I do see 717.1.2.1, which states if a duct connects more than 2 stories it can not be in a shaft. I wonder if the AHJ would consider the attic in this scenario to be a story... maxing out the two floor requirement. The attic is unfinished.
 
rosegamble said:
I do see 717.1.2.1, which states if a duct connects more than 2 stories it can not be in a shaft.
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That's not what my 717.1.2.1 says.

717.1.2.1 Ducts That Penetrate Nonfire-Resistance-Rated Assemblies​


The space around a duct penetrating a nonfire-resistance-rated floor assembly shall comply with Section 717.6.3.
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717.6.3 Nonfire-Resistance-Rated Floor Assemblies​


Duct systems constructed of approved materials in accordance with the International Mechanical Code that penetrate nonfire-resistance-rated floor assemblies shall be protected by any of the following methods:
  1. A shaft enclosure in accordance with Section 713.
  2. The duct connects not more than two stories, and the annular space around the penetrating duct is protected with an approved noncombustible material that resists the free passage of flame and the products of combustion.
  3. In floor assemblies composed of noncombustible materials, a shaft shall not be required where the duct connects not more than three stories, the annular space around the penetrating duct is protected with an approved noncombustible material that resists the free passage of flame and the products of combustion and a fire damper is installed at each floor line.
    Exception: Fire dampers are not required in ducts within individual residential dwelling units.
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If the equipment is in an attic and serves both the first and second stories, the duct connnects more than two stories and has to be protected by one of these three methods.
 
rosegamble said:
I see 713.1.2 in the 2021 BC (the applicable code) but this is for "unconcealed" openings and my commentary indicates this does not apply to ductwork with walls around them.
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That’s a typo, it’s 712.1.2 (Individual Dwelling Unit.) But you are correct, “unconcealed” is the key word as noted in the commentary, so you have a shaft per 712.1.1. There is additional commentary regarding 712.1.2 in the IBC Illustrated Handbook that says, “Concealed spaces used for installation of ducts, piping, and conduit between stories do not fall under this allowance.”

redeyedfly said:
If you start in the right place, 717.1.2.1
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Don’t we first have to confirm if a shaft is required, that would be in 712 Vertical Openings.

rosegamble said:
If a shaft containing mechanical ducts is running exclusively through a unit without sharing a shaft wall or branching into another residential unit, does it have to be rated like a traditional shaft wall?
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Yes, it has to be a “traditional” shaft wall per IBC 713.
 
Yankee Chronicler said:
If the equipment is in an attic and serves both the first and second stories, the duct connnects more than two stories and has to be protected by one of these three methods.
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Where are you an inspector? I want to be sure to never build anything where you have any authority whatsoever.

Go read the definition of a story.
 
walker.t said:
Wouldn’t two stories and an attic be considered more than two stories?
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Yes...Sorta....but it wouldn't be 3 stories...Which is what the code section is trying to prevent I believe and commentary uses the language of one floor penetration is 2 stories and 2 floors is 3.....
 
redeyedfly said:
No. Please see Chapter 2, "Story"
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Yes, I did check that before making my post, I agree that the definition of “Story” excludes attics, and that the definition of “Attic” is clearly not a “Story.”

My question was to clarify if “more than two stories” included an attic in addition to the stories, such that Story 1 + Story 2 + Attic is considered “more than two stories” because it includes something in addition to the two stories. Your “No” lets me know that you believe the intention in the code is that only stories are counted.

This might be a weak comparison, but I guess it’s kind of like someone saying, “Do you have more than two dollars?” and the other person says, “Yes.” then shows the first person two dollar bills and a quarter. How literally should the question be taken, should only dollar bills (floors) be counted?
 
steveray said:
Yes...Sorta....but it wouldn't be 3 stories...Which is what the code section is trying to prevent I believe and commentary uses the language of one floor penetration is 2 stories and 2 floors is 3.....
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With the equipment in an attic, you have to do a floor-ceiling assembly penetration, plus a membrane penetration or an attic floor-ceiling penetration, depending on how the attic is constructed. All options connect more than two stories, which would only penetrate one floor-ceiling assembly.
 
Attic is defined as: "The space between the ceiling framing of the top story and the underside of the roof." Does the attic have a floor or habitable space? It wouldn't be considered a story if it didn't.
 
walker.t said:
Yes, I did check that before making my post, I agree that the definition of “Story” excludes attics, and that the definition of “Attic” is clearly not a “Story.”

My question was to clarify if “more than two stories” included an attic in addition to the stories, such that Story 1 + Story 2 + Attic is considered “more than two stories” because it includes something in addition to the two stories. Your “No” lets me know that you believe the intention in the code is that only stories are counted.

This might be a weak comparison, but I guess it’s kind of like someone saying, “Do you have more than two dollars?” and the other person says, “Yes.” then shows the first person two dollar bills and a quarter. How literally should the question be taken, should only dollar bills (floors) be counted?
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The definition is unambiguous, the attic is part of the story immediately below it. The reason they have that in the definition is for this purpose. No one is going to claim you don't meet Table 504.4 because they counted the attic.
 
Yankee Chronicler said:
With the equipment in an attic, you have to do a floor-ceiling assembly penetration, plus a membrane penetration or an attic floor-ceiling penetration, depending on how the attic is constructed. All options connect more than two stories, which would only penetrate one floor-ceiling assembly.
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Where in the code does equipment in the attic make it a story?

Or maybe just stop for a minute and think about why we protect penetrations, why shafts are required sometimes and then why an attic would be irrelevant.
 
Paul Sweet said:
Attic is defined as: "The space between the ceiling framing of the top story and the underside of the roof." Does the attic have a floor or habitable space? It wouldn't be considered a story if it didn't.
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No, in that case it's not a story. But it's still outside of (beyond) the second story. It would then be a roof-ceiling assembly. With the equipment in the attic, penetrating the ceiling portion would me a membrane penetration. The applicable criterion from 717.6.3 is:

The duct connects not more than two stories, and the annular space around the penetrating duct is protected with an approved noncombustible material that resists the free passage of flame and the products of combustion.
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Look at the exception of 717.6.3. If none of the assemblies are required to be rated with fire barriers going from lowest level floor to roof deck, its all within an individual dwelling unit, no dampers needed. Unless its habitable space, the attic is not a story, so no shaft needed. Any enclosure to conceal the duct is now simply a chase, not a rated shaft.
Now if the dwelling unit separation doesn't continue all the way through, that changes things, but then the horizontal assemblies would more than likely be rated. A little more info may be needed on how the building is constructed.
 
I can see where the concern lies of the fire racing to the attic and burning the roof off before anyone knows, but hey, whatever....If it was important, it would be required to be fire rated....
 
klarenbeek said:
Look at the exception of 717.6.3. If none of the assemblies are required to be rated with fire barriers going from lowest level floor to roof deck, its all within an individual dwelling unit, no dampers needed. Unless its habitable space, the attic is not a story, so no shaft needed. Any enclosure to conceal the duct is now simply a chase, not a rated shaft.
Now if the dwelling unit separation doesn't continue all the way through, that changes things, but then the horizontal assemblies would more than likely be rated. A little more info may be needed on how the building is constructed.
Click to expand...

That exception applies only to condition #3, which is only applicable to non-combustible floor-ceiling assemblies.
 
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