IBC 717.5.2 Exception 3
The 1-hour fire barrier exception (IBC 717.5.2 Exception 3)
Ducts through a fire barrier normally need a fire damper. This exception drops the damper for fully ducted steel HVAC systems in sprinklered buildings, where the fire barrier is rated 1 hour or less.
Rules last reviewed October 12, 2026. How the rules are checked
Check your case in the tool (2024 IBC)Start the tool with the 2021 IBC · Start the tool with the 2018 IBC
Conditions
The tool applies the exception only when every one of these is true:
- The fire barrier’s required fire-resistance rating is 1 hour or less.
- The building is sprinklered throughout with an NFPA 13 or NFPA 13R system (IBC 903.3.1.1 or 903.3.1.2).
- Neither side of the wall is a Group H area.
- The penetration is a duct of the building’s HVAC system, not an air transfer opening.
- The fire barrier is not a horizontal exit. A horizontal exit is rated at least 2 hours (IBC 1026.2), so it fails the 1-hour test.
- The ductwork meets the checklist below.
Does the HVAC duct system meet all of these?
2018 IBC only
This exception lets ducts pass through low-rated fire barriers in sprinklered buildings without a damper, when the steel ductwork is continuous.
The exception applies only when every item is met:
- It is a ducted HVAC system carrying supply, return or exhaust air
- The ducts are sheet steel, No. 26 gage or thicker
- The steel ductwork is continuous from the air handling equipment to the air outlets and inlets
IBC 717.5.2 Exc. 3
2021 and 2024 IBC
This exception lets ducts pass through low-rated fire barriers in sprinklered buildings without a damper, when the steel ductwork is continuous.
The exception applies only when every item is met:
- It is a fully ducted HVAC system carrying supply, return or exhaust air
- The ducts are sheet steel, No. 26 gage or thicker
- The steel ductwork is continuous from the air handling equipment to the air outlets and inlets (nonmetal flexible connectors are allowed only at the air handler in the mechanical room, and between an overhead metal duct and a ceiling diffuser in the same room)
IBC 717.5.2 Exc. 3
What the tool returns when it applies
Fire damper: not required2021 and 2024 IBC
Fire damper: not required. The fire barrier is rated 1 hour or less, the building is fully sprinklered, neither side is a Group H area, and the duct is a fully ducted steel HVAC system that is continuous from the equipment to the outlets. IBC 717.5.2 Exc. 3
Also: Where no damper is required, the duct penetration must still be firestopped so the wall keeps its rating (through-penetration or membrane-penetration protection). IBC 717.1.2, IBC 714.3 to 714.4.3
Full result in the tool: No damper required
Fire damper: not required2018 IBC only
Fire damper: not required. The fire barrier is rated 1 hour or less, the building is fully sprinklered, neither side is a Group H area, and the duct is a ducted steel HVAC system that is continuous from the equipment to the outlets. IBC 717.5.2 Exc. 3
Also: Where no damper is required, the duct penetration must still be firestopped so the wall keeps its rating (through-penetration or membrane-penetration protection). IBC 717.1.2, IBC 714.3 to 714.4.3
Full result in the tool: No damper required
What changed in 2021
Since 2021 the exception says fully ducted and expressly allows nonmetal flexible air connectors at the air handler connection and between an overhead metal duct and a ceiling diffuser in the same room. The similar fire partition exception (717.5.4 Exc. 4) did not change.
| Edition | Requirement |
|---|---|
| 2018 IBC 717.5.2 Exc. 3 | No fire damper is needed where the fire barrier is rated 1 hour or less, the area is not Group H, the building is fully sprinklered (903.3.1.1 or 903.3.1.2) and the wall is crossed by a ducted HVAC system: No. 26 gage sheet steel ducts running continuously from the air handler to the outlets and inlets. The exception does not mention flexible air connectors, and Section 717.7 keeps them from passing through any wall. |
| 2021 IBC 717.5.2 Exc. 3 | No fire damper is needed where the fire barrier is rated 1 hour or less, the area is not Group H, the building is fully sprinklered (903.3.1.1 or 903.3.1.2) and the wall is crossed by a fully ducted HVAC system: No. 26 gage sheet steel ducts running continuously from the air handler to the outlets and inlets. Nonmetal flexible air connectors are allowed only at the air handler connection in the mechanical room (IMC 603.9) and between an overhead metal duct and a ceiling diffuser in the same room (IMC 603.6.2). |
| 2024 IBC 717.5.2 Exc. 3 | No fire damper is needed where the fire barrier is rated 1 hour or less, the area is not Group H, the building is fully sprinklered (903.3.1.1 or 903.3.1.2) and the wall is crossed by a fully ducted HVAC system: No. 26 gage sheet steel ducts running continuously from the air handler to the outlets and inlets. Nonmetal flexible air connectors are allowed only at the air handler connection in the mechanical room (IMC 603.9) and between an overhead metal duct and a ceiling diffuser in the same room (IMC 603.6.2). |
See this topic in the edition comparison
Common situations by edition
| Situation | 2024 IBC | 2021 IBC | 2018 IBC |
|---|---|---|---|
| Duct through a 1-hour fire barrier, NFPA 13 sprinklers, fully ducted steel HVAC system | No damper required | No damper required | No damper required |
| Same, with NFPA 13R sprinklers | No damper required | No damper required | No damper required |
| Duct through a 1-hour fire barrier, steel ductwork not continuous to the outlets | Fire damper required | Fire damper required | Fire damper required |
| Duct through a 1-hour fire barrier, building not fully sprinklered | Fire damper required | Fire damper required | Fire damper required |
| Duct through a 1-hour fire barrier next to a Group H area | Fire damper required | Fire damper required | Fire damper required |
| Duct through a 2-hour fire barrier, no exception applies | Fire damper required | Fire damper required | Fire damper required |
Select a result to open it in the tool with every answer filled in, including the conditions not listed here.
The similar exception for fire partitions
Fire partitions have a parallel exception (IBC 717.5.4 Exception 4) for ducted steel HVAC systems in sprinklered buildings. It did not change in 2021.
Fire damper: not requiredAll three editions
Fire damper: not required. The fire partition is rated 1 hour or less, the building is fully sprinklered, and the duct is a ducted steel HVAC system that is continuous from the equipment to the outlets. IBC 717.5.4 Exc. 4
Also: Where no damper is required, the duct penetration must still be firestopped so the wall keeps its rating (through-penetration or membrane-penetration protection). IBC 717.1.2, IBC 714.3 to 714.4.3
Full result in the tool: No damper required
Questions
Does the exception work in a 2-hour fire barrier?
No. The fire barrier must be rated 1 hour or less.
Fire damper: requiredAll three editions
Fire damper: required. Ducts and air transfer openings through a fire barrier need a listed fire damper, and none of the exceptions apply. IBC 717.5.2
Full result in the tool: Fire damper required
Does NFPA 13R count as fully sprinklered for this exception?
Yes. Both NFPA 13 and NFPA 13R systems throughout the building qualify.
Fire damper: not required2021 and 2024 IBC
Fire damper: not required. The fire barrier is rated 1 hour or less, the building is fully sprinklered, neither side is a Group H area, and the duct is a fully ducted steel HVAC system that is continuous from the equipment to the outlets. IBC 717.5.2 Exc. 3
Also: Where no damper is required, the duct penetration must still be firestopped so the wall keeps its rating (through-penetration or membrane-penetration protection). IBC 717.1.2, IBC 714.3 to 714.4.3
Full result in the tool: No damper required
Fire damper: not required2018 IBC only
Fire damper: not required. The fire barrier is rated 1 hour or less, the building is fully sprinklered, neither side is a Group H area, and the duct is a ducted steel HVAC system that is continuous from the equipment to the outlets. IBC 717.5.2 Exc. 3
Also: Where no damper is required, the duct penetration must still be firestopped so the wall keeps its rating (through-penetration or membrane-penetration protection). IBC 717.1.2, IBC 714.3 to 714.4.3
Full result in the tool: No damper required
Does the exception cover air transfer openings?
No. It covers ducts of a fully ducted HVAC system only. Transfer grilles in the fire barrier still need fire dampers.
Fire damper: requiredAll three editions
Fire damper: required. Ducts and air transfer openings through a fire barrier need a listed fire damper, and none of the exceptions apply. IBC 717.5.2
Full result in the tool: Fire damper required
Can the exception apply to a horizontal exit?
No. A horizontal exit is rated at least 2 hours (IBC 1026.2), so it fails the 1-hour test, and it also needs a smoke damper.
Fire damper: required · Smoke damper: requiredAll three editions
Fire damper: required. Ducts and air transfer openings through a fire barrier need a listed fire damper, and none of the exceptions apply. IBC 717.5.2
Smoke damper: required. The fire barrier serves as a horizontal exit, so a listed smoke damper is required. IBC 717.5.2.1
Full result in the tool: Combination fire/smoke damper required