IBC 717.6.2
Ceiling radiation dampers in rated roof/ceiling assemblies (IBC 717.6.2)
Ducts and diffusers that penetrate the rated ceiling below a roof need a ceiling radiation damper unless an exception applies. A duct through a rated roof slab with no rated ceiling below needs no damper.
What counts as a rated roof/ceiling: A fire-resistance-rated roof assembly or the rated ceiling below a roof.
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.
Ceiling radiation damper
- 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
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
- IBC 717.6 covers the ceiling membrane of a roof/ceiling assembly rather than the roof deck, so no damper is required for a duct through a rated roof slab with no rated ceiling below. The penetration must still be protected under IBC 714 so the roof keeps its rating (IBC 717.1.2). IBC 717.6, IBC 717.1.2, IBC 714.5 to 714.6.2
Common situations by edition
| Situation | 2024 IBC | 2021 IBC | 2018 IBC |
|---|---|---|---|
| Duct through the rated ceiling below a roof | Ceiling radiation damper required | Ceiling radiation damper required | Ceiling radiation damper required |
| Ceiling diffuser with no duct attached, in a rated roof/ceiling | Ceiling radiation damper required | Ceiling radiation damper required | Ceiling radiation damper required |
| Duct through a rated roof slab with no rated ceiling below | No damper required | No damper required | No damper required |
| Rated roof/ceiling design tested without ceiling radiation dampers | No damper required | No damper required | No damper required |
| Bathroom exhaust rising in a wall cavity into the rated ceiling, not passing through another unit | No damper required | No damper required | No damper required |
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.
What does the duct pass through?
- The rated ceiling below the roof.
- Only the rated roof deck or slab, with no rated ceiling below. For example a duct straight up through a rated concrete roof slab. If the roof rating depends on a ceiling or membrane on the underside, choose the ceiling option.
IBC 717.6
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
- Ceiling radiation dampers: dynamic and static: Since 2021 separate sections cover dynamic and static ceiling radiation dampers, with control options for static ones.
Questions
Does a ceiling diffuser below a rated roof need a ceiling radiation damper?
Ceiling radiation damper: requiredAll three editions
Ceiling radiation damper: required. 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
Full result in the tool: Ceiling radiation damper required
Does a duct through a rated concrete roof slab need a damper?
Not covered by IBC 717.6 where there is no rated ceiling below. Protect the penetration under IBC 714 (717.1.2).
No damper requiredAll three editions
IBC 717.6 covers the ceiling membrane of a roof/ceiling assembly rather than the roof deck, so no damper is required for a duct through a rated roof slab with no rated ceiling below. The penetration must still be protected under IBC 714 so the roof keeps its rating (IBC 717.1.2). IBC 717.6, IBC 717.1.2, IBC 714.5 to 714.6.2
Static or dynamic ceiling radiation damper?
Use a damper labeled for dynamic systems where the fans keep running during a fire. Since 2021 static dampers are allowed where the system is not designed to operate during a fire, or with one of three controls: a duct smoke detector within 5 feet of a damper at a duct opening, smoke detection in the same room or area for a damper in a ceiling, or an occupant sensor in the room that shuts the system down (IBC 717.2.3, 717.6.2.1.2).