CFC · California Fire Code

What special rules apply to ducts that penetrate fire walls or horizontal exits?

Q: Do ducts ever pass through a fire wall?

Only in limited cases. The baseline rule is no penetrations ; penetrations not on a lot line are allowed only if they comply with § 706.11 and then must meet the protection requirements in § 717 (fire dampers, listings, access) .

Q: If the wall is a horizontal exit, is a fire damper enough?

No. If the fire wall serves as a horizontal exit , the code requires a listed smoke damper at each duct or air transfer opening that penetrates that wall ( § 717.5.1.1 ) — a smoke damper is required to resist passage of smoke; provide a combination damper if both fire and smoke protection are needed .

Q: Can I put a fire damper in an exhaust duct to meet firewall rules?

Generally no. The CFC specifically states that exhaust ducts shall not penetrate fire walls and that fire dampers shall not be installed in exhaust ducts ; exhaust penetrations must usually be contained in a rated shaft or handled under specific exceptions (CFC § 2703.14.2) .

Ducts are normally not allowed through a fire wall. If a penetration is permitted, the California Fire Code requires listed dampers and specific installation, testing and access rules — and if the wall is a horizontal exit you must use a listed smoke damper at every penetration.

Ask a question free See coverage

Last reviewed: July 6, 2026

What the code requires — 2–4 sentences

Ducts and air transfer openings normally shall not penetrate a fire wall; penetrations are only allowed where the opening complies with the rules in § 706.11 and the protection requirements of § 717. Where a duct is permitted to pass a fire wall, it must be protected with a listed fire damper when the opening is in a fire wall (§ 717.5.1) and, if that fire wall serves as a horizontal exit, a listed smoke damper designed to resist the passage of smoke is required at each penetration (§ 717.5.1.1) .

The single most important rule: ducts generally do not go through fire walls — if they are allowed, you must follow § 717’s damper and listing requirements (and add a smoke damper where the wall is a horizontal exit).

Requirements in detail

Scope and baseline prohibition

Fire wall: ducts and air transfer openings shall not penetrate a fire wall except as allowed by § 706.11 (i.e., penetrations not on a lot line allowed only if they comply with § 717) .
If a penetration is permitted under § 706.11, the protective devices and installation rules in § 717 apply (dampers, listings, access, etc.) .

Dampers required (what kind and when)

Fire dampers are required for ducts and air transfer openings that are permitted to penetrate fire walls per § 717.5.1 (when penetrations are allowed under § 706.11) .
Smoke dampers — specifically required where the fire wall also serves as a horizontal exit: at each point a duct or air transfer opening penetrates that wall a listed smoke damper designed to resist smoke passage must be provided (§ 717.5.1.1) .
Where both fire and smoke protection are required, provide a combination fire/smoke damper or both devices as required by § 717.5 .

Ratings, testing, listing and installation

Dampers must be listed and labeled and installed per their listing and the installation rules in § 717.2–717.3 (UL standards are referenced for testing: e.g., UL 555 for fire dampers, UL 555S for smoke dampers) .
Access for inspection/maintenance is required; dampers with fusible links/internal operators need an access door at least 12 inches (305 mm) square or a removable duct section per § 717.4.1 .

Special material/size thresholds that affect when dampers are not required

Some alternative construction or small-duct criteria in related provisions (fire partitions / other assemblies) create exceptions — these are decision-relevant and summarized below.

Condition / dimension	Required action	Code reference
Ducts generally penetrating a fire wall — prohibited unless allowed under § 706.11 and protected per § 717	Do not penetrate, unless following § 706.11 and providing required dampers per § 717	§ 706.11, § 717.5.1
Fire wall openings: max 156 sq ft each; aggregate width at a floor ≤ 25% of wall length	Openings must meet size limits and be protected per § 716; duct penetrations count toward these limits	§ 706.8
Where firewall serves as horizontal exit	Provide a listed smoke damper at each penetration	§ 717.5.1.1
Access to dampers	Provide approved means of access; access door not less than 12 in (305 mm) square when required	§ 717.4.1
Small ducts (exceptions applicable to fire partitions, not to fire walls) — ≤ 100 sq in and certain material/installation criteria	May avoid fire damper if all exception conditions met (steel thickness, sleeve, annular fill, installed above ceiling, etc.)	§ 717.5.4 exceptions; see § 717.5.4 details
Duct wall thickness thresholds referenced in exceptions: No. 26 gage (~0.0187 in) or 0.0217 in (0.55 mm) depending on exception	Material thresholds determine when exception applies (refer to the exception text)	§ 717.5.4 exceptions
Exhaust ducts and fire walls / barriers	Exhaust ducts shall not penetrate fire walls; fire dampers shall not be installed in exhaust ducts	CFC § 2703.14.2 (exhaust ducts) and related CBC provisions

(Use the table rows to decide — e.g., if the opening is in a fire wall that also is a horizontal exit, you must add a smoke damper per § 717.5.1.1 .)

Installation & coordination notes

Do not install mechanical, electrical or plumbing controls through dampers unless allowed by the manufacturer and listing (§ 717.2.4.1) .
If a fire damper would interfere with an approved smoke control system, provide an approved alternate protection (see § 717.2.1 and the smoke control provisions in § 909) .
Dampers must be accessible and identified (labels “FIRE DAMPER”, “SMOKE DAMPER”, etc.) per § 717.4 .

Exceptions & special cases

Penetrations that are part of a fire-resistance-rated assembly and were tested as part of that assembly (ASTM E119 / UL 263) may not require a separate fire damper — follow the exception language in § 717 and related sections (the test as part of the assembly is the basis) .
Ducts that are part of an approved smoke control system may be exempt from a fire or smoke damper if the damper would interfere with the system’s operation; an approved alternative protection must be provided (§ 717.2.1) .
For exhaust ducts: the CFC explicitly restricts exhaust ducts from penetrating fire walls and indicates fire dampers shall not be installed in exhaust ducts — these are treated differently and often must be contained in rated shafts instead (CFC § 2703.14.2) .
Some smaller ducts or fully ducted HVAC systems in sprinklered buildings qualify for exceptions (material, thickness, continuous run, sleeves, annular filling, etc.); these exceptions are assembly- and occupancy-dependent — consult the specific exception text in § 717.5 and § 706 for applicability .

Common mistakes

Assuming any duct may penetrate a fire wall: by default ducts do not penetrate fire walls — you must check § 706.11 before planning a penetration .
Installing a fire damper in an exhaust duct or in a shaft that must maintain continuous upward airflow — the code prohibits dampers that would stop required continuous airflow and fire dampers are not permitted in certain exhaust ducts (see § 717.5.3.1 and CFC § 2703.14.2) .
Forgetting the smoke damper requirement where the wall is a horizontal exit (this is a distinct requirement in § 717.5.1.1) .
Neglecting access and labeling: dampers need an access opening and a permanent exterior label per § 717.4 — missing these will fail inspection .
Using the fire-partition small-duct exception for a true fire wall without verifying the exception’s scope — the small-duct exceptions often apply to partitions (see § 717.5.4) not fire walls; confirm which assembly you are dealing with .

Worked example — concrete scenario

Scenario: A building has a rated fire wall (not on a lot line) that will separate two tenant areas. You need a 12-inch round supply duct to pass from Unit A to Unit B through that fire wall to supply Unit B.

Step-by-step code application:

Confirm the baseline: § 706.11 says ducts shall not penetrate fire walls unless the penetration complies with § 717 — because this fire wall is not on a lot line and you intend a penetration, you must follow § 717 requirements .
Determine required damper: because it is a duct penetrating a fire wall and the exception allows penetration only if protected, provide a listed fire damper at the penetration in accordance with § 717.5.1 and the damper’s listing (UL 555) .
Check whether the fire wall is part of a horizontal exit: if yes, you must instead provide a listed smoke damper at that penetration (or a combination fire/smoke damper) per § 717.5.1.1 . If the wall is not a horizontal exit, the fire-damper-only requirement under § 717.5.1 applies .
Access & labeling: provide an access opening (or removable duct section) sized per § 717.4.1 (minimum 12 in × 12 in (305 mm) when fusible links/internal operators are present) and label the access per § 717.4.2 .
Material/size checks: the 12-inch round duct has an area ≈ 113 sq in, well below the large opening limits in § 706.8 (which controls openings in fire walls: 156 sq ft) — but those limits are for openings generally; you still must provide the damper protection required by § 717 for firewall penetrations permitted by § 706.11 .
If this were an exhaust duct instead of supply: CFC § 2703.14.2 and related rules prohibit exhaust ducts from penetrating fire walls and prohibit installing fire dampers in exhaust ducts — the correct approach would be to route the exhaust through a rated shaft or otherwise meet the CFC/CBC shaft requirements instead (do not put a fire damper in the exhaust duct) .

Related provisions (quick list)

§ 706 — Fire walls: openings, penetrations and limits (see § 706.8, § 706.9, § 706.11) .
§ 717.1 — General rules for ducts and air transfer openings (shaft transitions, penetrations without dampers) .
§ 717.2 — Installation rules; interaction with smoke control systems (§ 909) .
§ 717.3 — Damper testing, ratings and actuation (UL standards) .
§ 717.4 — Access and identification for dampers (minimum access door size, labeling) .
§ 717.5.1 — Ducts permitted in fire walls must be protected with listed fire dampers (when allowed) .
§ 717.5.1.1 — Smoke damper required at penetrations where the fire wall serves as a horizontal exit .
§ 716 — Opening protectives (used for openings through fire walls) .
CFC § 2703.14.2 — Exhaust ducts: containment in rated shafts; exhaust ducts shall not penetrate fire walls; fire dampers not for exhaust ducts .

Code references

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

CFC § 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.

7-36 2025 CALIFORNIA BUILDING CODE

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

FIRE AND SMOKE PROTECTION FEATURES
CFC § 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.

7-36 2025 CALIFORNIA BUILDING CODE

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

FIRE AND SMOKE PROTECTION FEATURES

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.
CFC § 706.7 High relevance — show source text
706.7 Combustible framing in fire walls. Adjacent combustible members entering into a concrete or masonry fire wall from opposite sides shall not have less than a 4-inch (102 mm) distance between embedded ends. Where combustible members frame into hollow walls or walls of hollow units, hollow spaces shall be solidly filled for the full thickness of the wall and for a distance not less than 4 inches (102 mm) above, below and between the structural members, with noncombustible materials approved for fireblocking.

706.8 Openings. Each opening through a fire wall shall be protected in accordance with Section 716 and shall not exceed 156 square feet (15 m [2] ). The aggregate width of openings at any floor level shall not exceed 25 percent of the length of the wall.

Exceptions:
1. Openings are not permitted in party walls constructed in accordance with Section 706.1.1.
2. Openings shall not be limited to 156 square feet (15 m [2] ) where both buildings are equipped throughout with an automatic sprinkler system installed in accordance with Section 903.3.1.1.
706.9 Penetrations. Penetrations of fire walls shall comply with Section 714.

706.10 Joints. Joints made in or between fire walls shall comply with Section 715.

706.11 Ducts and air transfer openings. Ducts and air transfer openings shall not penetrate fire walls.

Exception: Penetrations by ducts and air transfer openings of fire walls that are not on a lot line shall be allowed provided that the penetrations comply with Section 717. The size and aggregate width of all openings shall not exceed the limitations of Section 706.8.

SECTION 707—FIRE BARRIERS

707.1 General. Fire barriers installed as required elsewhere in this code or the California Fire Code shall comply with this section.

707.2 Materials. Fire barriers shall be of materials permitted by the building type of construction.

707.3 Fire-resistance rating. The fire-resistance rating of fire barriers shall comply with this section.

707.3.1 Shaft enclosures. The fire-resistance rating of the fire barrier separating building areas from a shaft shall comply with Section 713.4.

707.3.2 Interior exit stairway and ramp construction. The fire-resistance rating of the fire barrier separating building areas from an interior exit stairway or ramp shall comply with Section 1023.1.

707.3.3 Enclosures for exit access stairways. The fire-resistance rating of the fire barrier separating building areas from an exit access stairway or ramp shall comply with Section 713.4.

707.3.4 Exit passageway. The fire-resistance rating of the fire barrier separating building areas from an exit passageway shall comply with Section 1024.3.

707.3.5 Horizontal exit. The fire-resistance rating of the separation between building areas connected by a horizontal exit shall comply with Section 1026.1.

707.3.6 Atriums. The fire-resistance rating of the fire barrier separating atriums shall comply with Section 404.6.

707.3.7 Incidental uses. The fire barrier separating incidental uses from other spaces in the building shall have a fire-resistance rating of not less than that indicated in Table 509.1.
CFC § 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.
CFC § 415.6.5. High relevance — show source text
The aggregate quantity of pyrophoric gases in the building shall not exceed the amounts set forth in Table 415.6.5.
f. Quantity of Class 3 water-reactive solids in a single tool shall not exceed 1 pound.|

�

[F] 415.11.1.2 Separation. Fabrication areas, whose sizes are limited by the quantity of hazardous materials allowed by Table 415.11.1.1, shall be separated from each other, from corridors and from other parts of the building by not less than 1-hour fire barriers constructed in accordance with Section 707 or horizontal assemblies constructed in accordance with Section 711, or both.

Exceptions:
1. Doors within such fire barrier walls, including doors to corridors, shall be only self-closing fire door assemblies having a fire protection rating of not less than [3] / 4 hour.
2. Windows between fabrication areas and corridors are permitted to be fixed glazing listed and labeled for a fire protection rating of not less than [3] / 4 hour in accordance with Section 716.
[F] 415.11.1.3 Location of occupied levels. Occupied levels of fabrication areas shall be located at or above the first story above grade plane.

[F] 415.11.1.4 Floors. Except for surfacing, floors within fabrication areas shall be of noncombustible construction.

Openings through floors of fabrication areas are permitted to be unprotected where the interconnected levels are used solely for mechanical equipment directly related to such fabrication areas (see Section 415.11.1.5).

Floors forming a part of an occupancy separation shall be liquid tight.

[F] 415.11.1.5 Shafts and openings through floors. Elevator hoistways, vent shafts and other openings through floors shall be enclosed where required by Sections 712 and 713. Mechanical, duct and piping penetrations within a fabrication area shall not extend through more than two floors. The annular space around penetrations for cables, cable trays, tubing, piping, conduit or ducts shall be sealed at the floor level to restrict the movement of air. The fabrication area, including the areas through which the ductwork and piping extend, shall be considered to be a single conditioned environment.

[F] 415.11.1.6 Ventilation. Mechanical exhaust ventilation at the rate of not less than 1 cubic foot per minute per square foot

[0.0051 m [3] /(s × m [2] )] of floor area shall be provided throughout the portions of the fabrication area where HPM are used or stored. The exhaust air duct system of one fabrication area shall not connect to another duct system outside that fabrication area within the building.

A ventilation system shall be provided to capture and exhaust gases, fumes and vapors at workstations.

Two or more operations at a workstation shall not be connected to the same exhaust system where either one or the combination of the substances removed could constitute a fire, explosion or hazardous chemical reaction within the exhaust duct system.

Exhaust ducts penetrating fire barriers constructed in accordance with Section 707 or horizontal assemblies constructed in accordance with Section 711 shall be contained in a shaft of equivalent fire-resistance-rated construction. Exhaust ducts shall not penetrate fire walls.

Fire dampers shall not be installed in exhaust ducts.
CFC § 706.6.2 High relevance — show source text
FIRE AND SMOKE PROTECTION FEATURES

construction from both sides with openings protected by fire assemblies having a fire protection rating of not less than [3] / 4 hour. Portions of the exterior walls greater than 15 feet (4572 mm) above the lower roof shall be of nonfire-resistance-rated construction unless otherwise rated construction is required by other provisions of this code.

Exception: A fire wall serving as part of an exterior wall that separates buildings having different roof levels shall be permitted to terminate at the underside of the roof sheathing, deck or slab of the lower roof, provided that Items 1, 2 and 3 are met. The exterior wall above the fire wall is not required to be of fire-resistance-rated construction unless required by other provisions of this code.
1. The lower roof assembly within 10 feet (3048 mm) of the fire wall has not less than a 1-hour fire-resistance rating.
2. The entire length and span of supporting elements for the rated roof assembly shall have a fire -resistance rating of not less than 1 hour.
3. Openings in the lower roof shall not be located within 10 feet (3048 mm) of the fire wall.
706.6.2 Buildings with sloped roofs. Where a fire wall serves as an interior wall for a building, and the roof on one side or both sides of the fire wall slopes toward the fire wall at a slope greater than 2 units vertical in 12 units horizontal (2:12), the fire wall shall extend to a height equal to the height of the roof located 4 feet (1219 mm) from the fire wall plus 30 inches (762 mm). The extension of the fire wall shall be not less than 30 inches (762 mm).

706.7 Combustible framing in fire walls. Adjacent combustible members entering into a concrete or masonry fire wall from opposite sides shall not have less than a 4-inch (102 mm) distance between embedded ends. Where combustible members frame into hollow walls or walls of hollow units, hollow spaces shall be solidly filled for the full thickness of the wall and for a distance not less than 4 inches (102 mm) above, below and between the structural members, with noncombustible materials approved for fireblocking.

706.8 Openings. Each opening through a fire wall shall be protected in accordance with Section 716 and shall not exceed 156 square feet (15 m [2] ). The aggregate width of openings at any floor level shall not exceed 25 percent of the length of the wall.

Exceptions:
1. Openings are not permitted in party walls constructed in accordance with Section 706.1.1.
2. Openings shall not be limited to 156 square feet (15 m [2] ) where both buildings are equipped throughout with an automatic sprinkler system installed in accordance with Section 903.3.1.1.
706.9 Penetrations. Penetrations of fire walls shall comply with Section 714.

706.10 Joints. Joints made in or between fire walls shall comply with Section 715.

706.11 Ducts and air transfer openings. Ducts and air transfer openings shall not penetrate fire walls.

Exception: Penetrations by ducts and air transfer openings of fire walls that are not on a lot line shall be allowed provided that the penetrations comply with Section 717. The size and aggregate width of all openings shall not exceed the limitations of Section 706.8.

SECTION 707—FIRE BARRIERS
CFC § 415.11.1.5 High relevance — show source text
Floors forming a part of an occupancy separation shall be liquid tight.

[F] 415.11.1.5 Shafts and openings through floors. Elevator hoistways, vent shafts and other openings through floors shall be enclosed where required by Sections 712 and 713. Mechanical, duct and piping penetrations within a fabrication area shall not extend through more than two floors. The annular space around penetrations for cables, cable trays, tubing, piping, conduit or ducts shall be sealed at the floor level to restrict the movement of air. The fabrication area, including the areas through which the ductwork and piping extend, shall be considered to be a single conditioned environment.

[F] 415.11.1.6 Ventilation. Mechanical exhaust ventilation at the rate of not less than 1 cubic foot per minute per square foot

[0.0051 m [3] /(s × m [2] )] of floor area shall be provided throughout the portions of the fabrication area where HPM are used or stored. The exhaust air duct system of one fabrication area shall not connect to another duct system outside that fabrication area within the building.

A ventilation system shall be provided to capture and exhaust gases, fumes and vapors at workstations.

Two or more operations at a workstation shall not be connected to the same exhaust system where either one or the combination of the substances removed could constitute a fire, explosion or hazardous chemical reaction within the exhaust duct system.

Exhaust ducts penetrating fire barriers constructed in accordance with Section 707 or horizontal assemblies constructed in accordance with Section 711 shall be contained in a shaft of equivalent fire-resistance-rated construction. Exhaust ducts shall not penetrate fire walls.

Fire dampers shall not be installed in exhaust ducts.

[F] 415.11.1.7 Transporting hazardous production materials to fabrication areas. HPM shall be transported to fabrication areas through enclosed piping or tubing systems that comply with Section 415.11.7, through service corridors complying with Section 415.11.3, or in corridors as permitted in the exception to Section 415.11.2. The handling or transporting of HPM within service corridors shall comply with the California Fire Code .

4-46 2025 CALIFORNIA BUILDING CODE

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

SPECIAL DETAILED REQUIREMENTS BASED ON OCCUPANCY AND USE

[F] 415.11.1.8 Electrical. Electrical equipment and devices within the fabrication area shall comply with the California Electri- cal Code. The requirements for hazardous locations need not be applied where the average air change is not less than four times that set forth in Section 415.11.1.6 and where the number of air changes at any location is not less than three times that required by Section 415.11.1.6. The use of recirculated air shall be permitted.

[F] 415.11.1.8.1 Workstations. Workstations shall not be energized without adequate exhaust ventilation. See Section 415.11.1.6 for workstation exhaust ventilation requirements.

[F] 415.11.2 Corridors. Corridors shall comply with Chapter 10 and shall be separated from fabrication areas as specified in Section 415.11.1.2. Corridors shall not contain HPM and shall not be used for transporting such materials except through closed piping systems as provided in Section 415.11.7.4.
CFC § 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.

7-34 2025 CALIFORNIA BUILDING CODE

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

FIRE AND SMOKE PROTECTION FEATURES

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.
CFC § 2703.14.1 High relevance — show source text
2703.14.1 Where required. Exhaust ventilation systems shall be provided in the following locations in accordance with the requirements of this section and the California Building Code :
1. Fabrication areas: Exhaust ventilation for fabrication areas shall comply with the California Building Code . The fire code official is authorized to require additional manual control switches.
2. Workstations: A ventilation system shall be provided to capture and exhaust gases, fumes and vapors at workstations.
3. Liquid storage rooms: Exhaust ventilation for liquid storage rooms shall comply with Section 5004.3.1 and the California Building Code .
4. HPM rooms: Exhaust ventilation for HPM rooms shall comply with Section 5004.3.1 and the California Building Code .
5. Gas cabinets: Exhaust ventilation for gas cabinets shall comply with Section 5003.8.6.2. The gas cabinet ventilation system is allowed to connect to a workstation ventilation system. Exhaust ventilation for gas cabinets containing highly toxic or toxic gases shall also comply with Chapter 60.
6. Exhausted enclosures: Exhaust ventilation for exhausted enclosures shall comply with Section 5003.8.5.2. Exhaust ventilation for exhausted enclosures containing highly toxic or toxic gases shall also comply with Chapter 60.
7. Gas rooms: Exhaust ventilation for gas rooms shall comply with Section 5003.8.4.2. Exhaust ventilation for gas rooms containing highly toxic or toxic gases shall also comply with Chapter 60.
8. Cabinets containing pyrophoric liquids or Class 3 water-reactive liquids: Exhaust ventilation for cabinets in fabrication areas containing pyrophoric liquids or Class 3 water-reactive liquids shall be as required in Section 2705.2.3.4.
2703.14.2 Penetrations. Exhaust ducts penetrating fire barriers constructed in accordance with Section 707 of the California Building Code or horizontal assemblies constructed in accordance with Section 711 of the California Building Code shall be contained in a shaft of equivalent fire-resistance-rated construction. Exhaust ducts shall not penetrate fire walls. Fire dampers shall not be installed in exhaust ducts.

2703.14.3 Treatment systems. Treatment systems for highly toxic and toxic gases shall comply with Chapter 60.

2703.15 Emergency power system. An emergency power system shall be provided in Group H-5 occupancies in accordance with Section 1203. The emergency power system shall supply power automatically to the electrical systems specified in Section 2703.15.1 when the normal supply system is interrupted.

2703.15.1 Required electrical systems. Emergency power shall be provided for electrically operated equipment and connected control circuits for the following systems:
1. HPM exhaust ventilation systems.
2. HPM gas cabinet ventilation systems.
3. HPM exhausted enclosure ventilation systems.
4. HPM gas room ventilation systems.
5. HPM gas detection systems.
6. Emergency alarm systems.
7. Manual fire alarm systems.
8. Automatic sprinkler system monitoring and alarm systems.
9. Automatic alarm and detection systems for pyrophoric liquids and Class 3 water-reactive liquids required in Section 2705.2.3.4.
10. Flow alarm switches for pyrophoric liquids and Class 3 water-reactive liquids cabinet exhaust ventilation systems required in Section 2705.2.3.4.
11. Electrically operated systems required elsewhere in this code or in the California Building Code applicable to the use, storage or handling of HPM.
CFC § 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.
CFC § 2703.14.2 High relevance — show source text
2703.14.2 Penetrations. Exhaust ducts penetrating fire barriers constructed in accordance with Section 707 of the California Building Code or horizontal assemblies constructed in accordance with Section 711 of the California Building Code shall be contained in a shaft of equivalent fire-resistance-rated construction. Exhaust ducts shall not penetrate fire walls. Fire dampers shall not be installed in exhaust ducts.

2703.14.3 Treatment systems. Treatment systems for highly toxic and toxic gases shall comply with Chapter 60.

2703.15 Emergency power system. An emergency power system shall be provided in Group H-5 occupancies in accordance with Section 1203. The emergency power system shall supply power automatically to the electrical systems specified in Section 2703.15.1 when the normal supply system is interrupted.

2703.15.1 Required electrical systems. Emergency power shall be provided for electrically operated equipment and connected control circuits for the following systems:
1. HPM exhaust ventilation systems.
2. HPM gas cabinet ventilation systems.
3. HPM exhausted enclosure ventilation systems.
4. HPM gas room ventilation systems.
5. HPM gas detection systems.
6. Emergency alarm systems.
7. Manual fire alarm systems.
8. Automatic sprinkler system monitoring and alarm systems.
9. Automatic alarm and detection systems for pyrophoric liquids and Class 3 water-reactive liquids required in Section 2705.2.3.4.
10. Flow alarm switches for pyrophoric liquids and Class 3 water-reactive liquids cabinet exhaust ventilation systems required in Section 2705.2.3.4.
11. Electrically operated systems required elsewhere in this code or in the California Building Code applicable to the use, storage or handling of HPM.
2703.15.2 Exhaust ventilation systems. Exhaust ventilation systems are allowed to be designed to operate at not less than onehalf the normal fan speed on the emergency power system where it is demonstrated that the level of exhaust will maintain a safe atmosphere.

2703.16 Sub-atmospheric pressure gas systems. Sub-atmospheric pressure gas systems (SAGS) shall be in accordance with NFPA 318.

2025 CALIFORNIA FIRE CODE 27-7

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

SEMICONDUCTOR FABRICATION FACILITIES

SECTION 2704—STORAGE

2704.1 General. Storage of hazardous materials shall comply with Section 2703 and this section and other applicable provisions of this code.

2704.2 Fabrication areas. Hazardous materials storage and the maximum quantities of hazardous materials in use and storage allowed in fabrication areas shall be in accordance with Sections 2704.2.1 through 2704.2.2.1.

2704.2.1 Location of HPM storage in fabrication areas. Storage of HPM in fabrication areas shall be within approved or listed storage cabinets, gas cabinets, exhausted enclosures or within a workstation as follows:
1. Flammable and combustible liquid storage cabinets shall comply with Section 5704.3.2.
2. Hazardous materials storage cabinets shall comply with Section 5003.8.7.
3. Gas cabinets shall comply with Section 5003.8.6. Gas cabinets for highly toxic or toxic gases shall also comply with Section 6004.1.2.
CFC § 453.4.7 High relevance — show source text
453.4.7 Ventilation.

453.4.7.1 Compatibility. Incompatible materials shall not be conveyed in the same duct system. Combined products in mechani- cal exhaust ducts shall not create a physical hazard or reaction that could degrade the duct material. The building official may require a technical report in accordance with Section 453.7.1.

453.4.7.2 Fire dampers, smoke dampers and combination fire/smoke dampers. Fire dampers, smoke dampers or fire/smoke dampers shall not be permitted in mechanical exhaust duct systems used to maintain a safe laboratory environment. When the exhaust duct penetrates the laboratory suite boundary the exhaust duct shall be located within a horizontal or vertical assembly having a fire resistance rating equal to the fire barrier.

453.4.7.3 Reserved.

453.4.7.4 Laboratory suite exhaust air.

453.4.7.4.1 Exhaust air from laboratory suites shall not be recirculated.

453.4.7.4.2 Laboratory suite exhaust air shall be independently ducted to a point outside the building or an approved roof top structure.

Exception: Exhaust ducts serving separate laboratory suites may be connected to a common duct within a fire rated verti- cal shaft when the sub-duct extends vertically upward at least 22 inches.

453.4.7.4.3 Laboratory suite exhaust ducts shall not penetrate the fire barriers required by Section 453.4.1.

Exception: Where the exhaust duct is enclosed in a rated shaft in accordance with Section 713.

453.4.7.5 Ventilation rates. Mechanical exhaust ventilation systems shall provide a minimum ventilation rate not less than 1 cubic feet per minute per square foot [0.00508 m [3] /(s·m [2] ) ] of floor area, or 6 air exchanges per hour, whichever is greater. Systems shall operate continuously at the designed ventilation rate.

Exception: Refer to California Fire Code Section 5001.3 Performance-based design alternatives, as approved by the Fire Code Official.

453.4.7.6 Reserved.

453.4.7.7 Mechanical ventilation system balancing. Mechanical ventilation systems shall be designed and balanced such that during normal and emergency conditions the door opening forces comply with the requirements of Sections 1010.1.3 and Chapter 11B as applicable. Emergency conditions shall include: supply fan shutdown or failure, closing of smoke dampers or combination fire/smoke dampers, or emergency power.

453.5 Fire protection systems. See Chapter 9.

453.6 Means of egress.

453.6.1 Access to exits. Every room of a laboratory suite containing hazardous materials and having a floor area of 500 square feet (19 m2) or more shall have access to not less than two separate exits or exit-access doorways in accordance with Section 1006.2.

453.6.2 Door swing. All exit and exit-access doors serving areas with hazardous materials shall swing in the direction of exit travel, regardless of the occupant load served.

Frequently asked questions

Do ducts ever pass through a fire wall?

Only in limited cases. The baseline rule is no penetrations; penetrations not on a lot line are allowed only if they comply with § 706.11 and then must meet the protection requirements in § 717 (fire dampers, listings, access) .

If the wall is a horizontal exit, is a fire damper enough?

No. If the fire wall serves as a horizontal exit, the code requires a listed smoke damper at each duct or air transfer opening that penetrates that wall (§ 717.5.1.1) — a smoke damper is required to resist passage of smoke; provide a combination damper if both fire and smoke protection are needed .

Can I put a fire damper in an exhaust duct to meet firewall rules?

Generally no. The CFC specifically states that exhaust ducts shall not penetrate fire walls and that fire dampers shall not be installed in exhaust ducts; exhaust penetrations must usually be contained in a rated shaft or handled under specific exceptions (CFC § 2703.14.2) .

What about small ducts — can I avoid a damper if the duct is tiny?

Some small-duct exceptions exist (often within fire partitions rules), but they are conditional (size limits, material thickness, sleeves, annular fill, installed above ceiling, etc.). These exceptions are assembly- and occupancy-specific — do not assume they apply to fire walls without checking the exact exception text in § 717 and § 706 .

What access is required to the damper?

Dampers with fusible links or internal operators require an approved access door not less than 12 in (305 mm) square or a removable duct section; access must not reduce the assembly’s fire-resistance rating and must be labeled per § 717.4 .

Ask about the CFC

Get cited, plain-English answers on the California Fire Code for your project — any code section, any scenario.

Start Free Trial

Related in the CFC

When are fire dampers or smoke/air‑control dampers required at penetrations?

How do air‑transfer openings interact with smoke control systems and damper requirements?

Ducts, air‑transfer openings and required dampers

California Fire Code