CBC · California Building Code

How are ducts and air‑transfer openings protected to maintain compartmentation?

The CBC requires listed fire, smoke or combination dampers (or listed ceiling‑radiation or corridor dampers) where ducts or air‑transfer openings penetrate rated walls, shafts, corridors or smoke barriers so the fire‑ and smoke‑resisting function is preserved; exceptions and sizing limits apply, and installation, access and listing/testing per § 717, § 717.1 and § 717.5 must be followed. file

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Last reviewed: July 5, 2026

What the code requires — 2–4 sentences

The California Building Code (CBC) requires that ducts and air‑transfer openings that penetrate fire‑resistance or smoke‑control assemblies be protected so the assembly’s compartmentation and rating are preserved. Where the code requires protection, listed fire dampers, smoke dampers, combination fire/smoke dampers, ceiling radiation dampers or corridor dampers must be provided and installed per their listing and the manufacturer’s instructions (see § 717 and § 717.5) . Specific location rules for fire walls are in § 717.5.1 (fire dampers required at permitted duct openings) and for horizontal‑exit fire walls a smoke damper is required where a duct or air‑transfer opening penetrates that wall (§ 717.5.1.1) .

Requirements in detail

1) Basic rule and installation obligations

Dampers used to protect penetrations must be listed and installed in accordance with their listing and the manufacturer’s instructions; installation also must follow the specific CBC installation provisions in Section 717 (see § 717.2 and § 717.3) .
Where both fire and smoke protection are required, provide combination fire/smoke dampers or provide both a fire damper and a smoke damper (see § 717.5) .

Relevant testing and listing standards: fire dampers to UL 555; smoke dampers to UL 555S; combination to both standards (see § 717.3.1) .

2) Where specific damper types are required (high‑level summary)

Fire walls: ducts and air‑transfer openings permitted in fire walls must be protected with listed fire dampers (see § 717.5.1) .
Horizontal‑exit fire walls: where a fire wall serves as a horizontal exit, a listed smoke damper designed to resist smoke passage is required at each penetration (see § 717.5.1.1) .
Fire barriers / fire partitions: fire dampers are required at penetrations except where specific exceptions apply (see § 717.5.2 and § 717.5.4) .
Smoke barriers / smoke partitions / smoke‑separating walls: listed smoke dampers are required at each point a duct or air‑transfer opening penetrates (see § 717.5.5 and § 717.5.7) .
Shaft penetrations: where ducts are permitted to penetrate shaft enclosures, listed fire and smoke dampers are required unless an exception applies (see § 717.5.3) .
Membrane (ceiling) penetrations: ceiling radiation dampers are required where ducts or grille openings penetrate the ceiling membrane of a fire‑resistance‑rated floor/ceiling or roof/ceiling assembly (see § 717.6.2) .

3) Exceptions and alternative protection (highlights)

The CBC includes multiple exceptions where dampers are not required, for example:

Penetrations that are tested as part of the fire‑resistance‑rated assembly in accordance with ASTM E119 or UL 263 (penetration tested as part of the assembly) are exempt from requiring dampers (see exceptions in § 717.5.2 and other subsections) .
Ducts that are part of an approved smoke control system where a damper would interfere with the system operation may use approved alternate protection (see § 717.2.1 and exceptions in § 717.5.x) .
Under limited conditions, small steel ducts contained within a wall cavity and continuous from a dwelling unit to exterior may penetrate up to three floors without dampers if several dimensional and listing requirements are met (see § 717.6.1 exception) .

See the table below for the decision‑relevant numeric dimensions and limits called out in the exceptions and installation tables.

Decision‑relevant dimensions / values

Item	Value or requirement	Code Reference
Fire damper listing standard	UL 555	§ 717.3.1
Smoke damper listing standard	UL 555S	§ 717.3.1
Ceiling radiation damper testing/installation	Tested per § 717.3.1; installed per listing/manufacturer	§ 717.6.2.1 and § 717.3.1
Steel duct min thickness for 3‑floor exception	0.0187 in (No. 26 gage)	§ 717.6.1 (exception)
Max nominal duct diameter for 3‑floor exception	4 in (102 mm)	§ 717.6.1 (exception)
Max total area for small ducts (3‑floor exception)	100 in² per 100 ft² floor area	§ 717.6.1 (exception)
Annular‑space protection pressure for 3‑floor exception	Tested under min +0.01 in water (2.49 Pa)	§ 717.6.1 (exception)
Duct sleeve minimum length and thickness (fire partition exceptions)	12 in long by 0.060 in thick; retaining angles 1½"×1½"×0.060"	§ 717.5.4.1 and related exceptions
Minimum damper access opening	12 in × 12 in (305 mm square) or removable duct section	§ 717.4.1
Steel thickness where smoke dampers may be omitted in corridor ducts	0.019 in (0.48 mm)	§ 717.5.4.1 exceptions

(For full lists of exceptions and the exact text of each option, consult the referenced § 717 subsections in the CBC.)

Exceptions & special cases

Ducts used as part of an approved smoke control system: if installing a fire or smoke damper would interfere with smoke control system performance, approved alternate protection may be used; the smoke control system’s performance must be addressed in the rational analysis required by § 909 (see § 717.2.1 and exception language through § 717.5.x) file.
Penetration tested as part of the assembly: if the penetration assembly (including the duct/terminal) is tested as part of the fire‑resistance assembly to ASTM E119 / UL 263, dampers are not required (see the Exceptions in § 717.5.2 and § 717.6.2) file.
Small continuous ducts in walls: the 3‑floor exception allows small steel ducts (No.26 gauge, ≤4" nominal, ≤100 in² total per 100 ft²) continuous from a unit to exterior to pass through up to three floors without dampers if annular space is protected and grilles have ceiling radiation dampers where required (§ 717.6.1 exception) .
Shafts with required continuous upward airflow: dampers must not be installed where continuous upward airflow is required and damper closure would break that airflow (see § 717.5.3.1 and shaft exceptions) .

If you are relying on an exception (for example smoke‑control system interference or tested penetration), document the rationale and the supporting test/listing or smoke control analysis at plan review.

Common mistakes

Assuming all penetrations are treated the same: location controls (fire wall vs. fire barrier vs. smoke barrier vs. corridor vs. partition) change whether a fire damper, smoke damper or combination is required — check § 717.5 and the specific sub‑section for the assembly type rather than applying a blanket rule .
Installing dampers that are not listed to the correct standard (e.g., installing a damper not listed to UL 555S where smoke resistance is required) — the code mandates listed and labeled dampers per § 717.3.1 .
Failing to provide adequate access for inspection and maintenance (minimum 12" square access or removable duct section, and access cannot reduce the assembly rating) as required by § 717.4.1 and § 717.4.1.1 .
Using UL‑181 flexible/plastic ducts where the Mechanical Code or CBC prohibits their use for certain penetrations/risers — check the California Mechanical Code rules (see § 603.1.5 of the California Mechanical Code) .
Omitting smoke dampers because “there’s a damper somewhere else” — smoke and fire protection are separate functions; where both are required the code requires a combination damper or both devices per § 717.5 .

Worked example — concrete scenario

Scenario: A 3‑story apartment building has a metal supply duct (sheet steel) that penetrates a 2‑hour fire barrier between two dwelling units and continues into a corridor enclosure that must be smoke‑resisting. The duct is 6" nominal diameter and constructed of No. 26 gauge steel (0.0187").

Step 1 — Identify applicable sections:

Fire barrier penetrations: § 717.5.2 requires fire dampers at ducts penetrating fire barriers unless an exception applies .
Smoke barrier / corridor: § 717.5.5 and § 717.5.4.1 require smoke dampers where ducts penetrate smoke barriers or corridors that require smoke/draft control doors file.

Step 2 — Determine what to install:

Because the duct penetrates a fire barrier and also serves/penetrates a smoke‑resisting corridor, the assembly requires both fire and smoke protection. The code permits a listed combination fire/smoke damper (UL 555 + UL 555S) or separate listed devices (see § 717.5) .
Select a listed combination fire/smoke damper sized for a 6" round duct with the manufacturer’s listed installation detail.

Step 3 — Installation and access:

Install per the damper listing and manufacturer’s instructions and provide a minimum 12"×12" access door at the damper (see § 717.2 and § 717.4.1) file.
Ensure damper actuation and any smoke detection / actuation method meets the actuation requirements in § 717.3.3 if required for the specific application (see § 717.3 and § 717.3.3) .

Step 4 — Verify exceptions do not apply:

The small‑duct exceptions for omitting dampers require ducts ≤4" and other limits; this duct is 6" so the exception is not available (see § 717.6.1 exception) .

Result: Provide and install a listed combination fire/smoke damper at the barrier penetration, mounted and supported per the listing, with required access for inspection and testing, and documented in the submission.

Related provisions

§ 713 — Shaft enclosures (penetration and shaft rules referenced by § 717)
§ 714 — Penetrations (through‑penetration and membrane penetration protection methods and sleeve requirements)
§ 716 — Opening protectives (doors, smoke/draft control doors that interact with duct and smoke control requirements)
§ 717.3 — Damper testing, rating and actuation (UL standards and actuation rules)
§ 717.4 — Access and identification of dampers (access openings, labeling)
§ 717.6 — Horizontal assemblies and ceiling radiation dampers (membrane penetrations)
§ 909 — Smoke control systems and rational analysis (interactions with damper requirements and exceptions)
California Mechanical Code § 603 (installation and limitations for ducts, UL‑181, etc.)

Code references

Grounded in the retrieved California Building Code — click a citation to read the verbatim passage:

CBC § 0.0187 High relevance — show source text
Exception: In occupancies other than Groups I-2 and I-3, a duct is permitted to penetrate three floors or less without a fire damper at each floor, provided that such duct meets all of the following requirements:
1. The duct shall be contained and located within the cavity of a wall and shall be constructed of steel having a minimum wall thickness of 0.0187 inches (0.4712 mm) (No. 26 gage).
2. The duct shall open into only one dwelling unit or sleeping unit and the duct system shall be continuous from the unit to the exterior of the building.
3. The duct shall not exceed 4-inch (102 mm) nominal diameter and the total area of such ducts shall not exceed 100 square inches (0.065 m [2] ) in any 100 square feet (9.3 m [2] ) of floor area.
4. The annular space around the duct is protected with materials that prevent the passage of flame and hot gases sufficient to ignite cotton waste where subjected to ASTM E119 or UL 263 time-temperature conditions under a minimum positive pressure differential of 0.01 inch of water (2.49 Pa) at the location of the penetration for the time period equivalent to the fire-resistance rating of the construction penetrated.
5. Grille openings located in a ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly shall be protected with a listed ceiling radiation damper installed in accordance with Section 717.6.2.1.
717.6.2 Membrane penetrations. Ducts and air transfer openings constructed of approved materials in accordance with the Cali- fornia Mechanical Code that penetrate the ceiling membrane of a fire-resistance-rated floor/ceiling or roof/ceiling assembly shall be protected with one of the following:
1. A shaft enclosure in accordance with Section 713.
2. A listed ceiling radiation damper installed at the ceiling line where a duct penetrates the ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly. Exceptions:
3. A fire-resistance-rated assembly tested in accordance with ASTM E119 or UL 263 showing that ceiling radiation dampers are not required in order to maintain the fire-resistance rating of the assembly.
4. Where exhaust duct or outdoor air duct penetrations protected in accordance with Section 714.5.2 are located within the cavity of a wall and do not pass through another dwelling unit or tenant space.
5. Where duct and air transfer openings are protected with a duct outlet penetration system tested as part of a fire-resistance-rated assembly in accordance with ASTM E119 or UL 263.
6. A listed ceiling radiation damper installed at the ceiling line where a diffuser with no duct attached penetrates the ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly. Exceptions:
7. A fire-resistance-rated assembly tested in accordance with ASTM E119 or UL 263 showing that ceiling radiation dampers are not required in order to maintain the fire-resistance rating of the assembly.
8. Where duct and air transfer openings are protected with a duct outlet penetration system tested as part of a fire-resistance-rated assembly in accordance with ASTM E119 or UL 263.
717.6.2.1 Ceiling radiation dampers testing and installation. Ceiling radiation dampers shall be tested in accordance with Section 717.3.1. Ceiling radiation dampers shall be installed in accordance with the details specified in the fire-resistance-rated assembly and the manufacturer’s instructions and the listing.
CBC § 717.5.1 High relevance — show source text
717.5.1 Fire walls. Ducts and air transfer openings permitted in fire walls in accordance with Section 706.11 shall be protected with listed fire dampers installed in accordance with their listing.

717.5.1.1 Horizontal exits. A listed smoke damper designed to resist the passage of smoke shall be provided at each point a duct or air transfer opening penetrates a fire wall that serves as a horizontal exit.

717.5.2 Fire barriers. In other than Group A, E, H, I, L and R occupancies, high-rise buildings, and other applications listed in Section 1.11 regulated by the Office of the State Fire Marshal. Ducts and air transfer openings of fire barriers shall be protected with listed fire dampers installed in accordance with their listing. Ducts and air transfer openings shall not penetrate enclosures for interior exit stairways and ramps and exit passageways, except as permitted by Sections 1023.5 and 1024.6, respectively.

Exceptions: Fire dampers are not required at penetrations of fire barriers where any of the following apply:
1. Penetrations are tested in accordance with ASTM E119 or UL 263 as part of the fire-resistance-rated assembly.
2. Ducts are used as part of an approved smoke control system in accordance with Section 909 and where the use of a fire damper would interfere with the operation of a smoke control system.
3. Such walls are penetrated by fully ducted HVAC systems, have a required fire-resistance rating of 1 hour or less, are in areas of other than Group H and are in buildings equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1 or 903.3.1.2. For the purposes of this exception, a fully ducted HVAC system shall be a duct system for conveying supply, return or exhaust air as part of the structure’s HVAC system. Such a duct system shall be constructed of sheet steel not less than No. 26 gage thickness and shall be continuous from the air-handling appliance or equipment to the air outlet and inlet terminals. Nonmetal flexible air connectors shall be permitted in the following locations in accordance with Section 603 of the California Mechanical Code: 3.1. At the duct connection to the air handling unit or equipment located within the mechanical room. 3.2. From an overhead metal duct to a ceiling diffuser within the same room.
[SFM] For Group A, E, H, I, L and R occupancies, high-rise buildings, and other applications listed in Section 1.11 regulated by the Office of the State Fire Marshal, ducts and air transfer openings of fire barriers shall be protected with approved fire and smoke dampers installed in accordance with their listing. Ducts and air transfer openings shall not penetrate exit enclosures and exit passageways except as permitted by Sections 1023.5 and 1024.6, respectively.

Exceptions: 1. Fire dampers are not required at penetrations of fire barriers where penetrations are tested in accordance with ASTM E119 as part of the fire-resistance rated assembly.

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CBC § 3.1. High relevance — show source text
For the purposes of this exception, a fully ducted HVAC system shall be a duct system for conveying supply, return or exhaust air as part of the structure’s HVAC system. Such a duct system shall be constructed of sheet steel not less than No. 26 gage thickness and shall be continuous from the air-handling appliance or equipment to the air outlet and inlet terminals. Nonmetal flexible air connectors shall be permitted in the following locations in accordance with Section 603 of the California Mechanical Code: 3.1. At the duct connection to the air handling unit or equipment located within the mechanical room. 3.2. From an overhead metal duct to a ceiling diffuser within the same room.

[SFM] For Group A, E, H, I, L and R occupancies, high-rise buildings, and other applications listed in Section 1.11 regulated by the Office of the State Fire Marshal, ducts and air transfer openings of fire barriers shall be protected with approved fire and smoke dampers installed in accordance with their listing. Ducts and air transfer openings shall not penetrate exit enclosures and exit passageways except as permitted by Sections 1023.5 and 1024.6, respectively.

Exceptions: 1. Fire dampers are not required at penetrations of fire barriers where penetrations are tested in accordance with ASTM E119 as part of the fire-resistance rated assembly.

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2. Fire and smoke dampers are not required where ducts are used as part of an approved smoke control system in accordance with Section 909 and where the use of a fire or smoke damper would interfere with the operation of a smoke control system.

717.5.2.1 Horizontal exits. A listed smoke damper designed to resist the passage of smoke shall be provided at each point a duct or air transfer opening penetrates a fire barrier that serves as a horizontal exit.

717.5.3 Shaft enclosures. Shaft enclosures that are permitted to be penetrated by ducts and air transfer openings shall be protected with listed fire and smoke dampers installed in accordance with their listing.

Exceptions:
1. Fire dampers are not required at penetrations of shafts where any of the following criteria are met: 1.1. Steel exhaust subducts having a wall thickness of not less than 0.0187 inch (0.4712 mm) are extended not less than 22 inches (559 mm) vertically in exhaust shafts, and an exhaust fan is installed at the upper terminus of the shaft that is powered continuously in accordance with Section 909.11, so as to maintain a continuous upward airflow to the outdoors. 1.2. Penetrations are tested in accordance with ASTM E119 or UL 263 as part of the fire-resistance-rated assembly. 1.3. Ducts are used as part of an approved smoke control system designed and installed in accordance with Section 909 and where the fire damper will interfere with the operation of the smoke control system. 1.4. The penetrations are in parking garage exhaust or supply shafts that are separated from other building shafts by not less than 2-hour fire-resistance-rated construction.
CBC § 717.3.3.5 High relevance — show source text
717.3.3.5 Corridor damper actuation. Corridor damper actuation shall be in accordance with Sections 717.3.3.1 and 717.3.3.2.

717.4 Access and identification. Access and identification of fire and smoke dampers shall comply with Sections 717.4.1 through 717.4.2.

717.4.1 Access. Fire and smoke dampers shall be provided with an approved means of access that is large enough to permit inspection and maintenance of the damper and its operating parts. Dampers equipped with fusible links, internal operators, or both shall be provided with an access door that is not less than 12 inches (305 mm) square or provided with a removable duct section.

717.4.1.1 Access openings. The access shall not affect the integrity of fire-resistance-rated assemblies. The access openings shall not reduce the fire-resistance rating of the assembly. Access doors in ducts shall be tight fitting and suitable for the required duct construction.

717.4.1.2 Restricted access. Where space constraints or physical barriers restrict access to a damper for periodic inspection and testing, the damper shall be a single- or multi-blade type damper and shall comply with the remote inspection requirements of NFPA 80 or NFPA 105.

717.4.2 Identification. Access points shall be permanently identified on the exterior by a label having letters not less than [1] / 2 inch (12.7 mm) in height reading: “FIRE/SMOKE DAMPER,” “SMOKE DAMPER” or “FIRE DAMPER.”

717.5 Where required. Fire dampers, smoke dampers, combination fire/smoke dampers, ceiling radiation dampers and corridor dampers shall be provided at the locations prescribed in Sections 717.5.1 through 717.5.7 and 717.6. Where an assembly is required to have both fire dampers and smoke dampers, combination fire/smoke dampers or a fire damper and a smoke damper shall be provided.

717.5.1 Fire walls. Ducts and air transfer openings permitted in fire walls in accordance with Section 706.11 shall be protected with listed fire dampers installed in accordance with their listing.

717.5.1.1 Horizontal exits. A listed smoke damper designed to resist the passage of smoke shall be provided at each point a duct or air transfer opening penetrates a fire wall that serves as a horizontal exit.

717.5.2 Fire barriers. In other than Group A, E, H, I, L and R occupancies, high-rise buildings, and other applications listed in Section 1.11 regulated by the Office of the State Fire Marshal. Ducts and air transfer openings of fire barriers shall be protected with listed fire dampers installed in accordance with their listing. Ducts and air transfer openings shall not penetrate enclosures for interior exit stairways and ramps and exit passageways, except as permitted by Sections 1023.5 and 1024.6, respectively.

Exceptions: Fire dampers are not required at penetrations of fire barriers where any of the following apply:
1. Penetrations are tested in accordance with ASTM E119 or UL 263 as part of the fire-resistance-rated assembly.
2. Ducts are used as part of an approved smoke control system in accordance with Section 909 and where the use of a fire damper would interfere with the operation of a smoke control system.
CBC § 0.060 High relevance — show source text
2. The sleeve shall be secured to both sides of the wall and for all four sides of the sleeve with minimum 1 [1] / 2 -inch by 1 [1] / 2 -inch by 0.060-inch (38 mm by 38 mm by 1.52 mm) steel retaining angles. 3. The retaining angles shall be secured to the sleeve and the wall with No. 10 (M5) screws. 4. The annular space between the steel sleeve and the wall opening shall be filled with mineral wool batting on all sides.

717.5.4.1 Corridors. In other than Group A, E, H, I, L and R occupancies, high-rise buildings, and other applications listed in Section 1.11 regulated by the Office of the State Fire Marshal, duct and air transfer openings that penetrate corridors shall be protected with dampers as follows:
1. A corridor damper shall be provided where corridor ceilings, constructed as required for the corridor walls as permitted in Section 708.4, Exception 3, are penetrated.
2. A ceiling radiation damper shall be provided where the ceiling membrane of a fire-resistance-rated floor-ceiling or roof-ceiling assembly, constructed as permitted in Section 708.4, Exception 2, is penetrated.
3. A listed smoke damper designed to resist the passage of smoke shall be provided at each point a duct or air transfer opening penetrates a corridor enclosure required to have smoke and draft control doors in accordance with Section 716.2.2.1.
Exceptions:
1. Smoke dampers are not required where the building is equipped throughout with an approved smoke control system in accordance with Section 909, and smoke dampers are not necessary for the operation and control of the system.
2. Smoke dampers are not required in corridor penetrations where the duct is constructed of steel not less than 0.019 inch (0.48 mm) in thickness and there are no openings serving the corridor.
[SFM] For Group A, E, H, I, L and R occupancies, high-rise buildings, and other applications listed in Section 1.11 regulated by the Office of the State Fire Marshal, a listed smoke damper designed to resist the passage of smoke shall also be provided at each point a duct or air transfer opening penetrates a fire-resistance rated corridor enclosure required to have smoke and draft doors in accordance with Section 716.2.2.1 or doors that provide an effective barrier to limit the transfer of smoke in accordance with Section 407.3.1.

Exceptions: 1. Smoke dampers are not required where ducts are used as part of an approved mechanical smoke control system designed in accordance with Section 909 and where the smoke damper will interfere with the operation of the smoke control system. 2. Smoke dampers are not required in corridor penetrations where the duct is constructed of steel not less than 0.019 inch (0.48 mm) in thickness and there are no openings serving the corridor. 717.5.5 Smoke barriers. A listed smoke damper designed to resist the passage of smoke shall be provided at each point a duct or air transfer opening penetrates a smoke barrier. Smoke dampers and smoke damper actuation methods shall comply with Section 717.3.3.2.
CBC § 717.5.4 High relevance — show source text
717.5.4 Fire partitions. In other than Group A, E, I and R occupancies, high-rise buildings, and other applications listed in Section 1.11 regulated by the Office of the State Fire Marshal, ducts and air transfer openings that penetrate fire partitions shall be protected with listed fire dampers installed in accordance with their listing.

Exceptions: In occupancies other than Group H and L, fire dampers are not required where any of the following apply:
1. Corridor walls in buildings equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1 or 903.3.1.2 and the duct is protected as a through penetration in accordance with Section 714.
2. Tenant partitions in covered and open mall buildings where the walls are not required by provisions elsewhere in the code to extend to the underside of the floor or roof sheathing, slab or deck above.
3. The duct system is constructed of approved materials in accordance with the California Mechanical Code and the duct penetrating the wall complies with all of the following requirements: 3.1. The duct shall not exceed 100 square inches (0.06 m [2] ). 3.2. The duct shall be constructed of steel not less than 0.0217 inch (0.55 mm) in thickness.
3.3. The duct shall not have openings that communicate the corridor with adjacent spaces or rooms. 3.4. The duct shall be installed above a ceiling. 3.5. The duct shall not terminate at a wall register in the fire-resistance-rated wall. 3.6. A minimum 12-inch-long (305 mm) by 0.060-inch-thick (1.52 mm) steel sleeve shall be centered in each duct opening. The sleeve shall be secured to both sides of the wall and all four sides of the sleeve with minimum 1 [1] / 2 -inch by 1 [1] / 2 -inch by 0.060-inch (38 mm by 38 mm by 1.52 mm) steel retaining angles. The retaining angles shall be secured to the sleeve and the wall with No. 10 (M5) screws. The annular space between the steel sleeve and the wall opening shall be filled with mineral wool batting on all sides. 4. Such walls are penetrated by ducted HVAC systems, have a required fire-resistance rating of 1 hour or less, and are in buildings equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1 or 903.3.1.2. For the purposes of this exception, a ducted HVAC system shall be a duct system for conveying supply, return or

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exhaust air as part of the structure’s HVAC system. Such a duct system shall be constructed of sheet steel not less than No. 26 gage thickness and shall be continuous from the air-handling appliance or equipment to the air outlet and inlet terminals.

For Group A, E, I and R occupancies, high-rise buildings, and other applications listed in Section 1.11 regulated by the Office of the State Fire Marshal, ducts and air transfer openings that penetrate fire partitions shall be protected with listed fire dampers installed in accordance with their listings.
CBC § 717.1.1 High relevance — show source text
717.1.1 Ducts and air transfer openings. Ducts transitioning horizontally between shafts shall not require a shaft enclosure provided that the duct penetration into each associated shaft is protected with dampers complying with this section.

717.1.2 Ducts that penetrate fire-resistance-rated assemblies without dampers. Ducts that penetrate fire-resistance-rated walls and are not required by this section to have fire dampers shall comply with the requirements of Sections 714.3 through 714.4.3. Ducts that penetrate horizontal assemblies not required to be contained within a shaft and not required by this section to have fire dampers shall comply with the requirements of Sections 714.5 through 714.6.2.

717.1.2.1 Ducts that penetrate nonfire-resistance-rated assemblies. The space around a duct penetrating a nonfire-resistance-rated floor assembly shall comply with Section 717.6.3.

717.2 Installation. Fire dampers, smoke dampers, combination fire/smoke dampers and ceiling radiation dampers located within air distribution and smoke control systems shall be installed in accordance with the manufacturer’s instructions, the dampers’ listing and Sections 717.2.1 through 717.2.4.

717.2.1 Smoke control system. Where the installation of a fire damper will interfere with the operation of a required smoke control system in accordance with Section 909, approved alternative protection shall be utilized. Where mechanical systems including ducts and dampers utilized for normal building ventilation serve as part of the smoke control system, the expected performance of these systems in smoke control mode shall be addressed in the rational analysis required by Section 909.4.

717.2.2 Hazardous exhaust ducts. Fire dampers for hazardous exhaust duct systems shall comply with the California Mechanical Code .

717.2.3 Static dampers. Fire dampers and ceiling radiation dampers that are listed for use in static systems shall only be installed in heating, ventilation and air-conditioning systems that are automatically shut down in the event of a fire.

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717.2.4 Mechanical, electrical and plumbing controls. Mechanical, electrical and plumbing controls shall not be installed in air duct systems.

Exception: Controls where the wiring is directly associated with the air distribution system. The wiring shall comply with the requirements of Section 601 of the California Mechanical Code and be as short as practicable.

717.2.4.1 Controls not permitted to be installed through dampers. Mechanical, electrical and plumbing controls shall not be installed through fire dampers, smoke dampers, combination fire/smoke dampers or ceiling radiation dampers unless otherwise permitted by the manufacturer and the listing.

717.3 Damper testing, ratings and actuation. Damper testing, ratings and actuation shall be in accordance with Sections 717.3.1 through 717.3.3.

717.3.1 Damper testing. Dampers shall be listed and labeled in accordance with the standards in this section.
1. Fire dampers shall comply with the requirements of UL 555.
2. Smoke dampers shall comply with the requirements of UL 555S.
3. Combination fire/smoke dampers shall comply with the requirements of both UL 555 and UL 555S.
CBC § 10-51 High relevance — show source text
The minimum fire-resistance rating of the separation shall be 2 hours. Opening protectives in horizontal exits shall also comply with Section 716 of the California Building Code . Duct and air transfer openings in a fire wall or fire barrier that serves as a horizontal exit shall also comply with Section 717 of the California Building Code . The horizontal exit separation shall extend vertically through all levels of the building unless floor assemblies have a fire-resistance rating of not less than 2 hours and do not have unprotected openings.

Exception: A fire-resistance rating is not required at horizontal exits between a building area and an above-grade pedestrian walkway constructed in accordance with Section 3104 of the California Building Code, provided that the distance between connected buildings is more than 20 feet (6096 mm).

Horizontal exits constructed as fire barriers shall be continuous from exterior wall to exterior wall so as to divide completely the floor served by the horizontal exit.

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MEANS OF EGRESS

[BE] 1026.3 Opening protectives. Fire doors in horizontal exits shall be self-closing or automatic-closing when activated by a smoke detector in accordance with Section 716.2.6.6 of the California Building Code . Doors, where located in a cross-corridor condition, shall be automatic-closing by activation of a smoke detector installed in accordance with Section 716.2.6.6 of the California Building Code .

[BE] 1026.4 Refuge area. The refuge area of a horizontal exit shall be a space occupied by the same tenant or a public area and each such refuge area shall be adequate to accommodate the original occupant load of the refuge area plus the occupant load anticipated from the adjoining compartment. The anticipated occupant load from the adjoining compartment shall be based on the capacity of the horizontal exit doors entering the refuge area, or the total occupant load of the adjoining compartment, whichever is less.

[BE] 1026.4.1 Capacity. The capacity of the refuge area shall be computed based on a net floor area allowance of 3 square feet (0.2787 m [2] ) for each occupant to be accommodated therein. Where the horizontal exit also forms a smoke compartment, the capacity of the refuge area for Group I-2, I-3 and R-2.1 occupancies and Group B ambulatory care facilities shall comply with Sections 407.5.3, 408.6.2, 420.6.1, 420.6.2 and 422.3.2 of the California Building Code as applicable.

[BE] 1026.4.2 Number of exits. The refuge area into which a horizontal exit leads shall be provided with exits adequate to meet the occupant requirements of this chapter, but not including the added occupant load imposed by persons entering the refuge area through horizontal exits from other areas. In other than I-3 occupancies, not less than one refuge area exit shall lead directly to the exterior or to an interior exit stairway or ramp.

Exception: The adjoining compartment shall not be required to have a stairway or door leading directly outside, provided that the refuge area into which a horizontal exit leads has stairways or doors leading directly outside and are so arranged that egress shall not require the occupants to return through the compartment from which egress originates.
CBC § 1.11 High relevance — show source text
For Group A, E, I and R occupancies, high-rise buildings, and other applications listed in Section 1.11 regulated by the Office of the State Fire Marshal, ducts and air transfer openings that penetrate fire partitions shall be protected with listed fire dampers installed in accordance with their listings.

Exceptions: 1. Fire dampers are not required in corridor penetrations where the duct is constructed of steel not less than 0.019 inch (0.48 mm) in thickness, protected as a through penetration in accordance with Section 713 and there are no openings serving the corridor.

2. Fire dampers are not required where the duct system is constructed of approved materials in accordance with the Cali- fornia Mechanical Code and the duct penetrating the wall complies with all of the following requirements: 2.1. For other than corridors in Group I-2 occupancies the duct shall not exceed 100 square inches (0.6 m [2] ). 2.2. The duct shall be constructed of steel a minimum of 0.0217 inch (0.55 mm) in thickness.

2.3. The duct shall not have openings that communicate the corridor with adjacent spaces or rooms. 2.4. The duct shall be installed above a ceiling. 2.5. The duct shall not terminate at a wall register in the fire-resistance rated wall. 2.6. The duct shall be protected as a through penetration in accordance with Section 714 or shall comply with all of the following: 1. A minimum 12-inch-long (305 mm) by 0.060-inch-thick (1.52 mm) steel sleeve shall be centered in each duct opening.

2. The sleeve shall be secured to both sides of the wall and for all four sides of the sleeve with minimum 1 [1] / 2 -inch by 1 [1] / 2 -inch by 0.060-inch (38 mm by 38 mm by 1.52 mm) steel retaining angles. 3. The retaining angles shall be secured to the sleeve and the wall with No. 10 (M5) screws. 4. The annular space between the steel sleeve and the wall opening shall be filled with mineral wool batting on all sides.

717.5.4.1 Corridors. In other than Group A, E, H, I, L and R occupancies, high-rise buildings, and other applications listed in Section 1.11 regulated by the Office of the State Fire Marshal, duct and air transfer openings that penetrate corridors shall be protected with dampers as follows:
1. A corridor damper shall be provided where corridor ceilings, constructed as required for the corridor walls as permitted in Section 708.4, Exception 3, are penetrated.
2. A ceiling radiation damper shall be provided where the ceiling membrane of a fire-resistance-rated floor-ceiling or roof-ceiling assembly, constructed as permitted in Section 708.4, Exception 2, is penetrated.
3. A listed smoke damper designed to resist the passage of smoke shall be provided at each point a duct or air transfer opening penetrates a corridor enclosure required to have smoke and draft control doors in accordance with Section 716.2.2.1.
Exceptions:
CBC § 717.5.6 High relevance — show source text
Exception: Smoke dampers are not required where the openings in ducts are limited to a single smoke compartment and the ducts are constructed of steel. � 717.5.6 Exterior walls. Ducts and air transfer openings in fire-resistance-rated exterior walls required to have protected openings in accordance with Section 705.11 shall be protected with listed fire dampers installed in accordance with their listing.

7-38 2025 CALIFORNIA BUILDING CODE

on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

FIRE AND SMOKE PROTECTION FEATURES

717.5.7 Smoke partitions. A listed smoke damper designed to resist the passage of smoke shall be provided at each point that an air transfer opening penetrates a smoke partition. Smoke dampers and smoke damper actuation methods shall comply with Section 717.3.3.2.

Exception: Where the installation of a smoke damper will interfere with the operation of a required smoke control system in accordance with Section 909, approved alternative protection shall be utilized.

717.6 Horizontal assemblies. Penetrations by ducts and air transfer openings of a floor, floor/ceiling assembly or the ceiling membrane of a roof/ceiling assembly shall be protected by a shaft enclosure that complies with Section 713 or shall comply with Sections 717.6.1 through 717.6.3.

717.6.1 Through penetrations. A duct constructed of approved materials in accordance with the California Mechanical Code that penetrates a fire-resistance-rated floor/ceiling assembly that connects not more than two stories is permitted without shaft enclosure protection, provided that a listed fire damper is installed at the floor line or the duct is protected in accordance with Section 714.5. For air transfer openings, see Section 712.1.9.

Exception: In occupancies other than Groups I-2 and I-3, a duct is permitted to penetrate three floors or less without a fire damper at each floor, provided that such duct meets all of the following requirements:
1. The duct shall be contained and located within the cavity of a wall and shall be constructed of steel having a minimum wall thickness of 0.0187 inches (0.4712 mm) (No. 26 gage).
2. The duct shall open into only one dwelling unit or sleeping unit and the duct system shall be continuous from the unit to the exterior of the building.
3. The duct shall not exceed 4-inch (102 mm) nominal diameter and the total area of such ducts shall not exceed 100 square inches (0.065 m [2] ) in any 100 square feet (9.3 m [2] ) of floor area.
4. The annular space around the duct is protected with materials that prevent the passage of flame and hot gases sufficient to ignite cotton waste where subjected to ASTM E119 or UL 263 time-temperature conditions under a minimum positive pressure differential of 0.01 inch of water (2.49 Pa) at the location of the penetration for the time period equivalent to the fire-resistance rating of the construction penetrated.
5. Grille openings located in a ceiling of a fire-resistance-rated floor/ceiling or roof/ceiling assembly shall be protected with a listed ceiling radiation damper installed in accordance with Section 717.6.2.1.
CBC § 716.3.5.1 High relevance — show source text
716.3.5.1 Fire window frames. Fire window frames shall be approved for the intended application.

716.3.5.2 Labeling requirements. Fire-protection-rated glazing shall bear a label or other identification showing the name of the manufacturer, the test standard and information required in Section 716.1.2.2.2 and Table 716.1(3) that shall be issued by an approved agency and permanently identified on the glazing.

716.3.6 Installation. Fire window assemblies shall be installed in accordance with the provisions of this section.

716.3.6.1 Closure. Fire-protection-rated glazing shall be in the fixed position or be automatic-closing and shall be installed in labeled frames.

716.4 Fire protective curtain assembly. Approved fire protective curtain assemblies shall be constructed of any materials or assembly of component materials tested without hose stream in accordance with UL 10D, and shall comply with the Sections 716.4.1 through 716.4.3.

716.4.1 Label. Fire protective curtain assemblies used as opening protectives in fire-rated walls and smoke partitions shall be labeled in accordance with Section 716.2.9.

716.4.2 Smoke and draft control. Fire protective curtain assemblies used to protect openings where smoke and draft control assemblies are required shall comply with Section 716.2.1.4.

716.4.3 Installation. Fire protective curtain assemblies shall be installed in accordance with NFPA 80.

SECTION 717—DUCTS AND AIR TRANSFER OPENINGS

717.1 General. The provisions of this section shall govern the protection of duct penetrations and air transfer openings in assemblies required to be protected and duct penetrations in nonfire-resistance-rated floor assemblies.

717.1.1 Ducts and air transfer openings. Ducts transitioning horizontally between shafts shall not require a shaft enclosure provided that the duct penetration into each associated shaft is protected with dampers complying with this section.

717.1.2 Ducts that penetrate fire-resistance-rated assemblies without dampers. Ducts that penetrate fire-resistance-rated walls and are not required by this section to have fire dampers shall comply with the requirements of Sections 714.3 through 714.4.3. Ducts that penetrate horizontal assemblies not required to be contained within a shaft and not required by this section to have fire dampers shall comply with the requirements of Sections 714.5 through 714.6.2.

717.1.2.1 Ducts that penetrate nonfire-resistance-rated assemblies. The space around a duct penetrating a nonfire-resistance-rated floor assembly shall comply with Section 717.6.3.

717.2 Installation. Fire dampers, smoke dampers, combination fire/smoke dampers and ceiling radiation dampers located within air distribution and smoke control systems shall be installed in accordance with the manufacturer’s instructions, the dampers’ listing and Sections 717.2.1 through 717.2.4.

717.2.1 Smoke control system. Where the installation of a fire damper will interfere with the operation of a required smoke control system in accordance with Section 909, approved alternative protection shall be utilized. Where mechanical systems including ducts and dampers utilized for normal building ventilation serve as part of the smoke control system, the expected performance of these systems in smoke control mode shall be addressed in the rational analysis required by Section 909.4.
CBC § 717.5.2.1 High relevance — show source text
2. Fire and smoke dampers are not required where ducts are used as part of an approved smoke control system in accordance with Section 909 and where the use of a fire or smoke damper would interfere with the operation of a smoke control system.

717.5.2.1 Horizontal exits. A listed smoke damper designed to resist the passage of smoke shall be provided at each point a duct or air transfer opening penetrates a fire barrier that serves as a horizontal exit.

717.5.3 Shaft enclosures. Shaft enclosures that are permitted to be penetrated by ducts and air transfer openings shall be protected with listed fire and smoke dampers installed in accordance with their listing.

Exceptions:
1. Fire dampers are not required at penetrations of shafts where any of the following criteria are met: 1.1. Steel exhaust subducts having a wall thickness of not less than 0.0187 inch (0.4712 mm) are extended not less than 22 inches (559 mm) vertically in exhaust shafts, and an exhaust fan is installed at the upper terminus of the shaft that is powered continuously in accordance with Section 909.11, so as to maintain a continuous upward airflow to the outdoors. 1.2. Penetrations are tested in accordance with ASTM E119 or UL 263 as part of the fire-resistance-rated assembly. 1.3. Ducts are used as part of an approved smoke control system designed and installed in accordance with Section 909 and where the fire damper will interfere with the operation of the smoke control system. 1.4. The penetrations are in parking garage exhaust or supply shafts that are separated from other building shafts by not less than 2-hour fire-resistance-rated construction.
2. In Group B and R occupancies equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1, smoke dampers are not required at penetrations of shafts where all of the following criteria are met: 2.1. Kitchen, clothes dryer, bathroom and toilet room exhaust openings are installed with steel exhaust subducts, having a wall thickness of not less than 0.0187 inch (0.4712 mm). 2.2. The subducts extend not less than 22 inches (559 mm) vertically. 2.3. An exhaust fan is installed at the upper terminus of the shaft that is powered continuously in accordance with the provisions of Section 909.11, so as to maintain a continuous upward airflow to the outdoors.
3. Smoke dampers are not required at penetration of exhaust or supply shafts in parking garages that are separated from other building shafts by not less than 2-hour fire-resistance-rated construction.
4. Smoke dampers are not required at penetrations of shafts where ducts are used as part of an approved mechanical smoke control system designed in accordance with Section 909 and where the smoke damper will interfere with the operation of the smoke control system.
5. Fire dampers and combination fire/smoke dampers are not required in kitchen and clothes dryer exhaust systems where dampers are prohibited by the California Mechanical Code .
717.5.3.1 Continuous upward airflow. Fire dampers and smoke dampers shall not be installed in shafts that are required to maintain a continuous upward airflow path where closure of the damper would result in the loss of the airflow.

Frequently asked questions

Do I always need a damper where a duct passes through a rated wall?

Not always — the CBC requires dampers at many but not all penetrations; several exceptions exist (e.g., penetrations tested as part of the assembly, or ducts that are part of an approved smoke control system) so you must check the specific assembly type and the exceptions in § 717.5 and related subsections file.

When should I use a combination fire/smoke damper?

When a penetration is required to provide both fire resistance and smoke containment (the code requires both fire and smoke dampers at the same penetration), you may use a listed combination fire/smoke damper that meets both UL 555 and UL 555S, per § 717.5 and § 717.3.1 file.

What access is required for damper inspection?

Damper assemblies with fusible links or internal operators must have an approved access opening large enough for inspection — at least 12 in × 12 in (305 mm square) or a removable duct section; and the access must not reduce the fire‑resistance rating of the assembly (see § 717.4.1 and § 717.4.1.1) .

Can a damper be omitted if the building has an automatic sprinkler system?

Some exceptions allow omission of dampers where sprinklers and other specific conditions apply (see various exceptions in § 717.5.x). Whether the sprinkler system allows omission depends on the assembly type, occupancy, and the precise exception language in § 717.5 — verify the text for your condition .

If a smoke control system is required, can dampers be installed in those ducts?

If a damper would interfere with the operation of a required smoke control system, the CBC requires approved alternative protection and that the smoke control system performance be addressed in the rational analysis (see § 717.2.1 and § 909 references) file.

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