Duct chase in mixed use 2 story building. Can I call it a "two story opening"

[Fast_Edd1e]

I have a non-separated mixed use building. Fully fire suppressed. Wood framed. 2015 michigan building code. One portion of the building has 5 apartments above a business space. Apartments only need to be 1/2 hour rated since we are fully fire suppressed. Walls are 5/8 each side. Doors are rated. Ceiling is 5/8 on rc-1. Floor is 1.5" gypcrete.

Does the gypcrete compartmentalize the apartments or would the whole lower level need a 1 hour floor/ceiling assembly?

This brings me to the main question. We have a duct chase going from roof to lower level. Framers did not give enough space with their joists. So we are trying to avoid calling this a Shaft since its a wood joist and cant penetrate a shaft. This chase we can provide an access to so its not concealed. And its not on a corridor. And complies with all other requirements of 712.1.9 Two Story Openings. But if we have the entire floor/ceiling assembly below as rated and not covered by just the 1.5" gypcrete in the apartments, we would be penetrating a rated assembly. Which throws us into a Shaft and required to be rated.

Otherwise, im assuming the only option is to encapsulate the wood joist running thru the shaft to protect it. Which is difficult but doable.

 

[steveray]

The gypcrete is more about sound than fire I believe.....
Access panels do not make it "not concealed"
Wood exposed in the "shaft"? Make sure you get sprinklers in it or have a specific exemption from NFPA 13...

Good Luck!

 

[klarenbeek]

IMC 607.6.1 allows a duct to connect not more than two stories without a shaft if a fire damper is installed at the floorline.

 

[Fast_Edd1e]

IMC 607.6.1 allows a duct to connect not more than two stories without a shaft if a fire damper is installed at the floorline.

Hmm. That might help avoid calling it a rated shaft enclosure and alleviate our issues if we seal the duct off at the floor with a damper.

 

[classicT]

Fire burns upward. The fire protection of floor/ceiling assemblies is provided by the ceiling. The gypcrete floor is typically only for sound. Without the ceiling (gyp board), joists burn, floor falls, and the gypcrete does nothing.

 

[Yankee Chronicler]

Fire burns upward. The fire protection of floor/ceiling assemblies is provided by the ceiling. The gypcrete floor is typically only for sound. Without the ceiling (gyp board), joists burn, floor falls, and the gypcrete does nothing.

Correct -- mostly. You are correct that fire/heat [mostly] burns up and it is the ceiling that is important in a rated floor-ceiling assembly, BUT ... it's rare to find a rated ceiling. What we usually find in the U.L. Design book (or, now, web site) and in the Gypsum Association Handbook is rated floor-ceiling assemblies. It's the assembly that is rated, and if you remove any part of the assembly -- it's no longer a rated assembly.

 

[classicT]

Correct -- mostly. You are correct that fire/heat [mostly] burns up and it is the ceiling that is important in a rated floor-ceiling assembly, BUT ... it's rare to find a rated ceiling. What we usually find in the U.L. Design book (or, now, web site) and in the Gypsum Association Handbook is rated floor-ceiling assemblies. It's the assembly that is rated, and if you remove any part of the assembly -- it's no longer a rated assembly.

Correct. I simplified it down for the OP who did not appear to understand the concept.

 

[Paul Sweet]

There are a few systems, such as Gypsum Association #FC 5406 - 5408, where the "Ceiling provides one hour fire resistance protection for framing, including trusses."