Code changes
2021 IBC damper changes
Damper requirements in the 2021 International Building Code compared with the 2018 edition: 6 changed, 3 new, out of the 12 topics the edition comparison tracks. Each entry gives the requirement before and after, in plain language with the section numbers of both editions.
Rules last reviewed October 12, 2026. How the rules are checked
Fire barriers rated 1 hour or less
Changed
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.
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).
Exhaust subducts in shafts
Changed
Since 2021 the subduct needs a minimum steel thickness and the shaft needs a continuously powered exhaust fan.
2018 IBC 717.5.3 Exc. 1.1
No fire damper is needed where steel exhaust subducts extend at least 22 inches vertically in an exhaust shaft and air flows continuously upward to the outside. No subduct thickness or exhaust fan is specified.
2021 IBC 717.5.3 Exc. 1.1
No fire damper is needed where steel exhaust subducts at least 0.0187 inch thick extend at least 22 inches vertically in an exhaust shaft, and an exhaust fan at the top of the shaft runs on continuous power (909.11) to keep air moving upward to the outdoors.
Shafts with continuous upward airflow
New
New in 2021: dampers are prohibited where closing them would stop a required upward airflow.
2018 IBC
No such provision in this edition.
2021 IBC 717.5.3.1
Fire dampers and smoke dampers may not be installed in a shaft that has to keep a continuous upward airflow if closing the damper would stop that airflow.
Static and dynamic fire dampers
Changed
Since 2021 the testing list no longer requires a dynamic label for fire dampers; a new section limits static-listed dampers to systems that shut down in a fire.
2018 IBC 717.3.1 item 1
Fire dampers in HVAC systems designed to keep fans running during a fire must be labeled for dynamic systems.
2021 IBC 717.2.3
Fire dampers and ceiling radiation dampers listed for static systems may be installed only in HVAC systems that shut down automatically in a fire. The testing list no longer says that fire dampers must be labeled for dynamic systems.
Compare all three editions · Fire walls · Fire barriers · Rated corridors · Fire partitions
Ceiling radiation dampers: dynamic and static
Changed
Since 2021 separate sections cover dynamic and static ceiling radiation dampers, with control options for static ones.
2018 IBC 717.3.1 item 4
Ceiling radiation dampers in HVAC systems designed to keep fans running during a fire must be labeled for dynamic systems. No control options for static dampers are given.
2021 IBC 717.2.3, 717.6.2.1.1, 717.6.2.1.2
Ceiling radiation dampers in HVAC systems designed to keep fans running during a fire must be labeled for dynamic systems. Static dampers go in systems not designed to operate during a fire. The exceptions allow static dampers with one of these controls: a duct smoke detector within 5 feet of a damper at a duct opening (the damper must close when the fan shuts down where the detector needs airflow to work), 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.
Compare all three editions · Rated corridors · Rated floors · Rated roof/ceilings
Damper access
Changed
Since 2021 dampers with fusible links or internal operators need a 12-inch access door or a removable duct section.
2018 IBC 717.4
Provide approved access large enough to inspect and maintain the damper and its operating parts, without lowering the fire-resistance rating of the assembly; duct access doors must fit tightly. No minimum access door size is given.
2021 IBC 717.4.1, 717.4.1.1
Provide approved access large enough to inspect and maintain the damper and its operating parts, without lowering the fire-resistance rating of the assembly; duct access doors must fit tightly. Dampers with fusible links or internal operators need an access door at least 12 inches square or a removable duct section.
Restricted access
New
New in 2021: where access is restricted, use a blade-type damper with remote inspection.
2018 IBC
No such provision in this edition.
2021 IBC 717.4.1.2
Where tight space or physical obstructions prevent access for periodic inspection and testing, use a single- or multi-blade damper that can be inspected remotely as NFPA 80 or NFPA 105 requires.
Shafts into rooftop mechanical penthouses
New
New in 2021: no fire/smoke damper where a shaft rises into a rooftop penthouse and connects directly to the equipment.
2018 IBC
No such provision in this edition.
2021 IBC 713.12.1
No fire/smoke damper is needed where the shaft extends up through the roof into a rooftop structure that complies with Section 1511 and the ductwork in the shaft connects directly to the HVAC equipment.
Ducts in exit passageways
Changed
Since 2021 ductwork for independent ventilation, not only pressurization, may penetrate an exit passageway.
2018 IBC 1024.6
Penetrations of an exit passageway are limited to a short list of items. For ducts, that means equipment and ductwork needed for independent pressurization of the passageway.
2021 IBC 1024.6
Penetrations of an exit passageway are limited to a short list of items. For ducts, that means equipment and ductwork needed for independent ventilation or pressurization of the passageway.
More
- 2024 IBC damper changes
- Side-by-side comparison of the 2018, 2021 and 2024 IBC
- Overview of IBC Section 717
Plain-language summaries, not the code text. Editorial changes that do not affect where dampers are required are not listed. Local amendments and the authority having jurisdiction govern.