Vertical openings and duct penetrations

[Sifu]

I have a VB, 2 story with a basement building, non-sprinklered, using the 2018 IBC. The basement is unoccupied for mechanical equipment. I would consider it a story for the two-story opening provisions. The two upper floors are separated by a 2-hr horizontal assembly for separated occupancies (E below, B above).

They are sending ducts from the furnace in the basement to the 2nd & 3rd story via a shaft since 3 stories are penetrated. The shaft stops at the horizontal assembly above the E, then the ducts exit the shaft and run under the rated horizontal assembly to serve the 2nd and 3rd story. They propose to provide fire dampers at the ducts serving the 3rd story at the ceiling penetration of the 2nd floor.

They only propose a "fire damper" where the ducts penetrate the horizontal assembly. They show nothing for the penetration of the shaft, or the enclosure/damper at the bottom and nothing where the ducts penetrate the shaft wall.

Based on 717.5.3 I think the ducts that penetrate the shaft wall must be provided with fire/smoke dampers.
Based on 713.11 I think the bottom of the shaft would require a fire damper.
Based on 717.6.2 I think the ceiling membrane of the horizontal assembly must be protected with ceiling radiation dampers.

But, some of this seems redundant, so I am not sure. I simple-sketched out the conditions. Am I off base?

 

[Yankee Chronicler]

• The lower floor is unrated, so the duct shaft doesn't need a rated enclosure at the bottom. I would only require that the duct be metal and that it has a tightly-fitted flange where it passes through the floor-ceiling assembly. [Note: in your sketch, the shaft enclosure passes through the lower floor and terminates at the basement ceiling (if there is one). In reality, wouldn't it bear on the upper surface of the lower floor-ceiling assembly?]

• The shaft only connects the basement and the first floor. It terminates against the underside of the rated floor-ceiling assembly for the second floor. So it only needs to be rated 1-hour.
• I concur regarding the fire & smoke damper where the duct exits the shaft just below the rated floor-ceiling assembly.
• Your reference to 717.6.2 for the ceiling radiation dampers is incorrect. As drawn, the duct runs below the rated assembly, and the trucks extend through the entire floor-ceiling assembly. That's a through penetration, not a membrane penetration. You need to be looking at 717.6.1

 

[Sifu]

• The lower floor is unrated, so the duct shaft doesn't need a rated enclosure at the bottom. I would only require that the duct be metal and that it has a tightly-fitted flange where it passes through the floor-ceiling assembly. [Note: in your sketch, the shaft enclosure passes through the lower floor and terminates at the basement ceiling (if there is one). In reality, wouldn't it bear on the upper surface of the lower floor-ceiling assembly?]

The applicant has not provided a section of this, so it may be on the upper surface of the lower floor. This is the area I found redundant, not sure of the need for the damper/enclosure at the bottom if there is one at the top.

View attachment 13846

It is the "but not less than the rating required for the shaft enclosure" language that trips me up. 713.11 exc. #1 permits draftstop, but only if the only openings in the shaft are at the bottom, so I moved away from that.

• The shaft only connects the basement and the first floor. It terminates against the underside of the rated floor-ceiling assembly for the second floor. So it only needs to be rated 1-hour.
• I concur regarding the fire & smoke damper where the duct exits the shaft just below the rated floor-ceiling assembly.
• Your reference to 717.6.2 for the ceiling radiation dampers is incorrect. As drawn, the duct runs below the rated assembly, and the trucks extend through the entire floor-ceiling assembly. That's a through penetration, not a membrane penetration. You need to be looking at 717.6.1

I was unsure of the ceiling radiation damper vs. fire damper since the ducts that penetrate the lower membrane are not the same ducts that penetrate the upper surface of the floor. However they are connected. Happy with fire dampers.