Roof top ductwork required fire protection rating?

[mtlogcabin]

4 story existing hospital replacing 3 elevators with 2 compliant elevators and current code requirements in a single shaft. The fan and supply air ductwork required to pressurize the shaft is located on the roof to be compliant with 909.21.1.

Question 1: Is the ductwork located on the roof required to be protected with a two-hour fire rating?
Question 2: Would the fan and related ductwork located on the roof be part of the "fan system" and therefore 909.21.4.1 would negate the 909.21.3 requirement

Any thoughts?

2021 IBC

909.21.1​

Elevator hoistways shall be pressurized to maintain a minimum positive pressure of 0.10 inch of water (25 Pa) and a maximum positive pressure of 0.25 inch of water (67 Pa) with respect to adjacent occupied space on all floors. This pressure shall be measured at the midpoint of each hoistway door, with all elevator cars at the floor of recall and all hoistway doors on the floor of recall open and all other hoistway doors closed. The pressure differentials shall be measured between the hoistway and the adjacent elevator landing. The opening and closing of hoistway doors at each level must be demonstrated during this test. The supply air intake shall be from an outside, uncontaminated source located a minimum distance of 20 feet (6096 mm) from any air exhaust system or outlet.

909.21.3​

Any duct system that is part of the pressurization system shall be protected with the same fire-resistance rating as required for the elevator shaft enclosure.

909.21.4.1 ​

Where located within the building, the fan system that provides the pressurization shall be protected with the same fire-resistance rating required for the elevator shaft enclosure.

 

[steveray]

I would say that the more specific 909.21.4.1 would prevail and the implication would be that stuff outside the building would not need to be protected but I would have to spend some time before I went to the wall on that…

 

[Yankee Chronicler]

Are the fan and duct on the roof of the building, or on the roof of the elevator penthouse?

Does the roof-ceiling assembly have a fire-resistance rating?

 

[Gregg Harris]

4 story existing hospital replacing 3 elevators with 2 compliant elevators and current code requirements in a single shaft. The fan and supply air ductwork required to pressurize the shaft is located on the roof to be compliant with 909.21.1.

Question 1: Is the ductwork located on the roof required to be protected with a two-hour fire rating?
Question 2: Would the fan and related ductwork located on the roof be part of the "fan system" and therefore 909.21.4.1 would negate the 909.21.3 requirement

Any thoughts?

2021 IBC

909.21.1​

Elevator hoistways shall be pressurized to maintain a minimum positive pressure of 0.10 inch of water (25 Pa) and a maximum positive pressure of 0.25 inch of water (67 Pa) with respect to adjacent occupied space on all floors. This pressure shall be measured at the midpoint of each hoistway door, with all elevator cars at the floor of recall and all hoistway doors on the floor of recall open and all other hoistway doors closed. The pressure differentials shall be measured between the hoistway and the adjacent elevator landing. The opening and closing of hoistway doors at each level must be demonstrated during this test. The supply air intake shall be from an outside, uncontaminated source located a minimum distance of 20 feet (6096 mm) from any air exhaust system or outlet.

909.21.3​

Any duct system that is part of the pressurization system shall be protected with the same fire-resistance rating as required for the elevator shaft enclosure.

909.21.4.1 ​

Where located within the building, the fan system that provides the pressurization shall be protected with the same fire-resistance rating required for the elevator shaft enclosure.

The way I read it, 909.21.4.1 should not be considered since 21.3 states any duct system. So it should not matter if it is inside or on the roof.

 

[mtlogcabin]

Roof of the building, there is no elevator penthouse.

 

[Yankee Chronicler]

Roof of the building, there is no elevator penthouse.

Fire-resistance rating?

 

[mtlogcabin]

Type II B construction

 

[Yankee Chronicler]

Okay, so fan and ductwork both on top of the roof, roof-ceiling system has no fire-resistance rating.

IBC 909.21.3 requires that the duct system be protected to the same rating as the elevator shaft.

IBC 909.21.4.1 says the fan system shall be protected to the same rating as the elevator shaft if located within the building.

If the roof has no rating, the duct system has to be protected. If the fan is not located within the duct system, the fan system doesn't need to be fireproofed. If the fan is within the duct system -- the duct system has to be fireproofed, so the fan system goes along for the ride.