Damper Guide

Damper types

Ceiling radiation dampers: where the IBC requires them and what to specify

A ceiling radiation damper protects an opening in the ceiling membrane of a rated floor/ceiling or roof/ceiling assembly, usually above a diffuser or grille, from radiant heat that would otherwise reach the structure above.

Rules last reviewed October 12, 2026. How the rules are checked

Check which damper your penetration needs (2024 IBC)Start the tool with the 2021 IBC · Start the tool with the 2018 IBC

Standard, rating and actuation

Test standard
UL 555C
Rating
Listed to UL 555C or tested as part of the rated assembly. HVAC systems whose fans run during a fire need dampers labeled for dynamic systems.
Closes on
Heat, at 50°F above the normal duct temperature and at least 160°F.

IBC 717.3.1 item 4, 717.6.2, 717.6.2.1

Where the IBC requires a ceiling radiation damper

Where the IBC requires a ceiling radiation damper, unless an exception applies (each page lists the exceptions):

What to specify

2018 IBC only

  • Listed to UL 555C, or tested as part of the rated floor/ceiling or roof/ceiling assembly (ASTM E119 or UL 263)
  • Installed per the rated assembly details, the listing and the manufacturer’s instructions
  • Heat-responsive device 50°F above normal duct temperature, at least 160°F
  • If the HVAC fans run during a fire, the ceiling radiation damper must be labeled for dynamic systems

IBC 717.3.1 item 4, IBC 717.6.2.1, IBC 717.3.3.4

2021 and 2024 IBC

  • Listed to UL 555C, or tested as part of the rated floor/ceiling or roof/ceiling assembly (ASTM E119 or UL 263)
  • Installed per the rated assembly details, the listing and the manufacturer’s instructions
  • Heat-responsive device 50°F above normal duct temperature, at least 160°F
  • Labeled for dynamic systems if the HVAC fans run during a fire. Static dampers where the system is not designed to operate during a fire, or with one of these 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 717.3.1 item 4, IBC 717.6.2.1, IBC 717.3.3.4, IBC 717.2.3, 717.6.2.1.1, 717.6.2.1.2

Ceiling radiation damper vs fire damper

A fire damper protects the full thickness of a wall or the floor line. A ceiling radiation damper protects only the ceiling membrane of a rated floor/ceiling or roof/ceiling, and it is installed to the details of the rated design it is part of. More about the fire damper.

Static or dynamic

Ceiling radiation dampers in systems whose fans keep running during a fire must be labeled for dynamic systems. Since 2021 the general rule (IBC 717.2.3) allows static dampers where the system shuts down automatically in a fire, and the exceptions in IBC 717.6.2.1.2 also allow them 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. Only the occupant sensor option shuts the system down. IBC 717.2.3, 717.6.2.1.1, 717.6.2.1.2 (2021 and 2024), 717.3.1 item 4 (2018)

Installation basics

Rules for every damper type (installing to the listing, no flexible ducts through rated assemblies, no controls through dampers in 2024) are on the damper types page.

Questions

When is a ceiling radiation damper not required?

When the rated design was tested without one; when an exhaust or outdoor air duct in a wall cavity is protected as required by IBC 714.5.2 and does not run through any other dwelling unit or tenant space; or when a duct outlet system tested with the assembly is used.

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

Does a diffuser with no duct attached need one?

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 roof slab need one?

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

Illustration