IBC 717.6.1 and 717.6.2
Fire dampers and ceiling radiation dampers in rated floors (IBC 717.6)
A duct through a rated floor normally needs a shaft. A duct connecting only two stories may use a fire damper at the floor line instead (in the 2018 and 2021 IBC, not in Groups I-2 and I-3), and a duct that only enters the rated ceiling below needs a ceiling radiation damper.
What counts as a rated floor or floor/ceiling: A fire-resistance-rated floor, including the ceiling below it when that ceiling is part of the rated assembly. A floor that is a smoke barrier is also a rated floor.
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
When each damper is required
Every result the tool can give for a duct carrying heating, cooling or ventilation air, or an air transfer opening, through this assembly. Labels show where a result applies only to ducts, only to air transfer openings, or only in some editions.
Fire damper
- RequiredDucts only
A duct through a rated floor connecting only two stories may skip the shaft if a listed fire damper is placed at the floor line.
Or protect the duct as required by IBC 714.5 instead of the damper.
IBC 717.6.1
- Not requiredDucts only
The duct meets every item of the exception (a small steel duct in a wall cavity serving one dwelling or sleeping unit and running continuously to the outside) and penetrates no more than three floors, so fire dampers are not needed at the floors. The exception is not available in Groups I-2 and I-3.
IBC 717.6.1 Exception
Ceiling radiation damper
- RequiredDucts only
Grille openings in the ceiling of a rated floor/ceiling or roof/ceiling assembly need a listed ceiling radiation damper.
IBC 717.6.1 Exception item 5, IBC 717.6.2.1
- RequiredDucts only
Where a duct passes through the ceiling of the rated assembly, a listed ceiling radiation damper is required at the ceiling line.
Or enclose the duct in a shaft that complies with IBC 713.
IBC 717.6.2 item 2
- RequiredAir transfer openings only
A listed ceiling radiation damper is required at the ceiling line where an opening with no duct attached, such as a diffuser or grille, penetrates the ceiling of the rated assembly.
IBC 717.6.2, IBC 717.6.2 item 3
- Not required
The rated assembly was tested and shown not to need ceiling radiation dampers.
IBC 717.6.2 Exc. 1
- Not requiredDucts only
The exhaust or outdoor air duct is inside a wall cavity, protected as required by IBC 714.5.2, and does not run through any other dwelling unit or tenant space.
IBC 717.6.2 Exc. 2
- Not required
The opening is protected by a duct outlet penetration system that was tested with the rated assembly.
IBC 717.6.2 item 2 Exc. 3, IBC 717.6.2 item 3 Exc. 2
When a damper is not the answer
- Shaft enclosure requiredDucts only
A duct through two rated floors must be enclosed in a shaft. Only ducts connecting two stories may use a floor damper or firestop instead.
- Shaft enclosure requiredDucts only
A duct through three rated floors must be enclosed in a shaft. Only ducts connecting two stories may use a floor damper or firestop instead.
- Shaft enclosure requiredDucts only
A duct through four or more rated floors must be enclosed in a shaft. Only ducts connecting two stories may use a floor damper or firestop instead.
- Vertical opening rules applyAir transfer openings only
An air transfer opening through a floor is a vertical opening, not a damper question. It is allowed only inside a shaft enclosure or where a vertical opening rule in IBC 712.1 permits it.
- Shaft enclosure requiredDucts only, 2018 and 2021 IBC
In Group I-2 and I-3 occupancies, a duct through a rated floor must be enclosed in a shaft. The floor damper options do not apply.
Also required
- Flexible ducts and flexible air connectors may not pass through any fire-resistance-rated assembly, and flexible air connectors may not go through any wall, floor or ceiling at all. (ducts only) IBC 717.7
- Where no damper is required, the duct penetration must still be firestopped so the floor or ceiling keeps its rating (through-penetration or membrane-penetration protection). IBC 717.1.2, IBC 714.5 to 714.6.2
Common situations by edition
Select a result to open it in the tool with every answer filled in, including the conditions not listed here.
Exceptions and conditions the tool checks
These are the questions the tool asks, in order, with the explanation it gives. Section numbers are shown for each edition where they differ.
How does the duct pass through the rated floor/ceiling?
- Through the whole floor to another story. The duct passes through both the ceiling and the floor and connects stories.
- Only into the ceiling below the floor. The duct enters the ceiling, for example to reach a diffuser or grille, but does not pass through the floor above.
IBC 717.6
Is either story the duct connects, or any part of this floor, a Group I-2 or I-3 occupancy?
Group I-2 includes hospitals and nursing homes. Group I-3 includes jails and detention centers. Include I-2 or I-3 areas in mixed-use buildings.
How many floors does the duct pass through outside of a shaft?
What is the required fire-resistance rating of the assembly?
Use the rating the code requires for this wall or floor, shown on the life safety plans.
Does the duct meet all of these?
This exception is common for small bathroom and dryer exhaust ducts in apartments and hotels.
The exception applies only when every item is met:
- The duct is inside a wall cavity
- The duct is steel at least 0.0187 inch thick (No. 26 gage)
- The duct serves a single dwelling unit or sleeping unit and opens into no other
- The duct runs continuously from that unit to the outside of the building
- The duct is no larger than 4 inches nominal diameter
- Together these ducts are no more than 100 sq in. per 100 sq ft of floor area
- The gap around the duct is filled with materials that prevent flame and hot gases from igniting cotton waste under ASTM E119 or UL 263 fire exposure, with at least 0.01 inch of water positive pressure, for the rating of the floor
IBC 717.6.1 Exception
Does the duct have a grille opening in the ceiling of a rated floor/ceiling or roof/ceiling assembly?
IBC 717.6.1 Exception item 5
Was the rated floor/ceiling or roof/ceiling assembly tested (ASTM E119 or UL 263) in a way that shows it keeps its rating without ceiling radiation dampers?
Some listed assemblies, such as certain UL designs, allow unprotected duct openings. Check the listing for the assembly.
IBC 717.6.2 Exc. 1
Is it an exhaust or outdoor air duct inside a wall cavity, protected as required by IBC 714.5.2, that does not run through any other dwelling unit or tenant space?
Typical case: a bathroom or dryer exhaust duct rising inside a wall and entering the rated ceiling at the top plate on its way outside.
IBC 717.6.2 Exc. 2
Is the duct protected with a duct outlet penetration system that was tested with the rated assembly (ASTM E119 or UL 263)?
This is a specific outlet or boot system named in the listing of the rated floor/ceiling or roof/ceiling design. A generic fire-rated boot or duct wrap does not count. Answer yes only if the assembly listing names the system.
IBC 717.6.2 Exceptions
Code changes that affect this assembly
- Ducts through floors in Groups I-2 and I-3: In 2024 the Group I-2 and I-3 limit moved from the main rule to the three-floor exception.
- Ceiling radiation dampers: dynamic and static: Since 2021 separate sections cover dynamic and static ceiling radiation dampers, with control options for static ones.
Questions
Can a fire damper replace a shaft for a duct through a floor?
Only for a duct connecting two stories, and in the 2018 and 2021 IBC only outside Groups I-2 and I-3.
Fire damper: requiredAll three editions
Fire damper: required. A duct through a rated floor connecting only two stories may skip the shaft if a listed fire damper is placed at the floor line. Or protect the duct as required by IBC 714.5 instead of the damper. IBC 717.6.1
Full result in the tool: Fire damper at the floor line, or duct protection per IBC 714.5
When is a ceiling radiation damper required in a rated floor/ceiling?
Ceiling radiation damper: requiredAll three editions
Ceiling radiation damper: required. Where a duct passes through the ceiling of the rated assembly, a listed ceiling radiation damper is required at the ceiling line. Or enclose the duct in a shaft that complies with IBC 713. IBC 717.6.2 item 2
Full result in the tool: Ceiling radiation damper required
Can the rated assembly listing remove the ceiling radiation damper?
Yes, where the floor/ceiling design was tested and shown not to need one.
Ceiling radiation damper: not requiredAll three editions
Ceiling radiation damper: not required. The rated assembly was tested and shown not to need ceiling radiation dampers. IBC 717.6.2 Exc. 1
Also: Where no damper is required, the duct penetration must still be firestopped so the floor or ceiling keeps its rating (through-penetration or membrane-penetration protection). IBC 717.1.2, IBC 714.5 to 714.6.2
Full result in the tool: No damper required
What changed for hospitals and jails in 2024?
In 2024 the Group I-2 and I-3 limit applies only to the small duct exception, so a duct connecting two stories may use the floor damper option.
Fire damper at the floor line, or duct protection per IBC 714.52024 IBC only
A duct through a rated floor connecting only two stories may skip the shaft if a listed fire damper is placed at the floor line. IBC 717.6.1
Shaft enclosure required2018 and 2021 IBC
In Group I-2 and I-3 occupancies, a duct through a rated floor must be enclosed in a shaft. The floor damper options do not apply.