CBC · California Building Code

What combustible materials are permitted in Types I and II construction?

The CBC allows certain combustible materials in Types I and II buildings — principally fire‑retardant‑treated wood for select nonbearing and exterior uses, limited insulation with strict flame‑spread limits, and specific nonmetallic ducts, piping or electrically insulated components when installed under the Mechanical, Plumbing or Electrical Codes. Check § 603 and subsections for exact allowances and the cross‑references that add conditions and exceptions.

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Last reviewed: July 5, 2026

What the code requires

The California Building Code allows limited combustible materials in otherwise noncombustible Types I and II buildings when specifically listed and installed under the conditions in Section 603 and its subsections. The principal allowances are: fire‑retardant‑treated (FRT) wood for certain partitions, exterior walls, roof framing and limited exterior projections; specific classes of thermal/acoustical insulation; and limited combustible components in ducts, piping and electrical systems when installed under the referenced specialty codes. See § 603, § 603.1, § 603.1.1 and § 603.1.3 for the controlling language.

Requirements in detail

1) Fire‑retardant‑treated wood (FRT wood)

  • Permitted uses (per § 603.1):

    • Nonbearing partitions with required fire‑resistance rating of 2 hours or less (except within shaft enclosures in Group I‑2 and ambulatory care).
    • Nonbearing exterior walls where a fire‑resistance rating is not required.
    • Roof construction (girders, trusses, framing, decking).
    • Balconies, porches, decks and exterior stairways not used as required exits on buildings three stories or less above grade plane.

  • Notable exception: In buildings of Type IA that exceed two stories above grade plane, FRT wood is restricted in roof construction when the vertical distance from the upper floor to the roof is less than 20 ft. (See the exceptions in § 603.1.)

2) Insulation and other interior materials

  • Thermal and acoustical insulation (other than foam plastics) with a flame‑spread index ≤ 25 is permitted. Exceptions allow higher flame‑spread ratings in specific assemblies:

    • Insulation between two layers of noncombustible materials (without an airspace) may have flame spread ≤ 100.
    • Insulation installed between a finished floor and solid decking without airspace may have flame spread ≤ 200.

  • Foam plastics are addressed elsewhere (Chapter 26) and are not freely permitted here.

3) Mechanical, plumbing and electrical components

  • Nonmetallic ducts: permitted only where installed in accordance with the California Mechanical Code limitations (see § 603.1.1).
  • Combustible piping and plumbing fixtures: permitted where installed in accordance with the California Mechanical Code and the California Plumbing Code (see § 603.1.2).
  • Electrical wiring with combustible insulation, tubing, raceways and related components: permitted where installed in accordance with this code and the California Electrical Code (see § 603.1.3).

Decision‑relevant table

Application What combustible material may be used Limitation / condition Code reference
Nonbearing interior partitions Fire‑retardant‑treated wood Allowed when required fire‑resistance ≤ 2 hr; not in shafts of Group I‑2/ambulatory care § 603.1 (items 1, 1.1)
Nonbearing exterior walls Fire‑retardant‑treated wood Only where fire‑resistance rating is not required § 603.1 (item 1.2)
Roof framing (girders, trusses, decking) Fire‑retardant‑treated wood Allowed; see exception for Type IA roofs < 20 ft vertical clearance § 603.1 (item 1.3) and exception
Balconies/porches/decks (exterior, not required exits) Fire‑retardant‑treated wood Only on buildings ≤ 3 stories above grade plane (see related § 705 exception) § 603.1 (item 1.4) and § 705.2.3.1 exception
Thermal / acoustic insulation Non‑foam insulation with flame spread ≤ 25 Exceptions: ≤100 between noncombustible layers; ≤200 under finished floor solid decking § 603.1 (item 2)
Ducts Nonmetallic ducts (limited) Only if installed per California Mechanical Code § 603.1.1
Piping / plumbing fixtures Combustible piping materials permitted Per California Mechanical Code / California Plumbing Code § 603.1.2
Electrical wiring systems Wiring with combustible insulation permitted Must comply with this code and the California Electrical Code § 603.1.3

Exceptions & special cases

  • Type IA roofs: FRT wood is specifically restricted in roof construction for Type IA buildings exceeding two stories above grade plane when the vertical clearance from the upper floor to the roof is less than 20 ft. Read the exception in § 603.1 carefully.
  • Concealed spaces: generally combustible materials are not permitted in concealed spaces of Type I/II buildings, but Section 718.5 lists limited exceptions referring back to Section 603 and other provisions (e.g., plenums complying with the Mechanical Code, Class A interior finishes). If you plan to place combustible items in concealed spaces, confirm the specific exception that applies. § 718.5 cross‑references § 603.
  • Exterior wall coverings, balconies and projections have additional limits and testing/height/area constraints in Chapter 14 and in § 705; those provisions can further restrict use of combustible exterior materials even when § 603 allows them. See § 1405.1.1 and § 705.2.3.1 for related restrictions and exceptions.

If a material or installation is governed by the Mechanical, Plumbing or Electrical Code (for example, nonmetallic ducts, combustible piping, or wiring), compliance must meet those codes’ limitations as well as the CBC allowances in § 603.

Common mistakes

  • Treating Types I and II as absolutely “no combustible materials” — the code expressly lists permitted combustibles in § 603; omission of those allowances can lead to over‑design or unnecessary cost.
  • Applying the FRT wood allowances without checking the exceptions (Type IA roof vertical clearance, Group I‑2 shaft exclusions). Always verify the occupancy and construction subtype.
  • Forgetting cross‑code limits: using nonmetallic ducts or combustible piping without meeting the California Mechanical/Plumbing/Electrical Code restrictions referenced in §§ 603.1.1–603.1.3.
  • Assuming foam plastics are permitted with the same freedom as other insulation — foam plastics are regulated by Chapter 26 and are not covered by the general insulation allowances in § 603.1.
  • Neglecting concealed‑space rules: combustible materials in concealed spaces are generally prohibited except as specifically allowed; check § 718.5 when planning penetrations or services.

Worked example

Scenario: You are designing the roof framing for a 4‑story apartment building classified as Type IIA.

Applicable code points:

  • § 603.1 allows FRT wood for roof construction (girders, trusses, framing, decking). That allowance is not subject to the Type IA‑roof exception (the exception applies only to Type IA buildings). Therefore FRT wood roof framing is permitted in this Type IIA 4‑story building, provided the FRT complies with the referenced FRT standard (§ 2303.2) and other code requirements.

Numbers/checklist to verify:

  1. Confirm the building is Type IIA (not Type IA). (§ 602.2 and § 603.1 context).
  2. Use FRT wood that meets the requirements of Section 2303.2 (material standard and labeling). (§ 603.1 refers to FRT wood complying with § 2303.2).
  3. If any concealed roof spaces will contain combustible materials, confirm compliance with § 718.5 (concealed spaces) — e.g., sprinklering or noncombustible insulation may be required.

Result: FRT wood roof framing is code‑permitted for the 4‑story Type IIA example (subject to the above verifications).

Related provisions

  • § 603 — Combustible material in Types I and II construction (main allowance list).
  • § 603.1 — Allowable materials and detailed items (FRT wood, insulation limits, etc.).
  • § 603.1.1 — Ducts: nonmetallic ducts allowed per California Mechanical Code.
  • § 603.1.2 — Piping and plumbing fixtures: combustible piping allowed per Mechanical/Plumbing Codes.
  • § 603.1.3 — Electrical: combustible wiring/insulation allowed per California Electrical Code.
  • § 718.5 — Combustible materials in concealed spaces in Type I or II construction (exceptions referencing § 603).
  • § 705.2.3.1 — Balconies and similar projections (related allowances/limits for combustible balconies).
  • § 1405.1.1 — Combustible exterior wall coverings (limits on area, height and testing).
  • § 805 — Combustible materials on or embedded in floors of Types I and II construction (floor‑specific provisions).

Code references

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

  • CBC § 705.2.1 High relevance — show source text

    705.2.1 Types I and II construction. Projections from walls of Type I or II construction shall be of noncombustible materials or combustible materials as allowed by Sections 705.2.3.1 and 705.2.4.

    705.2.2 Type III, IV or V construction. Projections from walls of Type III, IV or V construction shall be of any approved material.

    705.2.3 Projection protection. Projections extending to 5 feet (1524 mm) or less from the line used to determine the fire separation distance shall be one of the following:

    1. Noncombustible materials.

    2. Combustible materials of not less than 1-hour fire-resistance-rated construction.

    3. Heavy timber construction complying with Section 2304.11.

    4. Fire-retardant-treated wood.

    5. As permitted by Section 705.2.3.1.

    Exception: Type VB construction shall be allowed for combustible projections in Group R-3 and U occupancies with a fire separation distance greater than or equal to 5 feet (1524 mm).

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    FIRE AND SMOKE PROTECTION FEATURES

    705.2.3.1 Balconies and similar projections. Balconies and similar projections of combustible construction other than fireretardant-treated wood shall be fire-resistance rated where required by Table 601 for floor construction or shall be of heavy timber construction in accordance with Section 2304.11. The aggregate length of the projections shall not exceed 50 percent of the building’s perimeter on each floor.

    Exceptions:

    1. On buildings of Types I and II construction, three stories or less above grade plane, fire-retardant-treated wood shall be permitted for balconies, porches, decks and exterior stairways not used as required exits.

    2. Untreated wood and plastic composites that comply with ASTM D7032 and Section 2612 are permitted for pickets, rails and similar guard components that are limited to 42 inches (1067 mm) in height.

    3. Balconies and similar projections on buildings of Types III, IV-HT and V construction shall be permitted to be of Type V construction and shall not be required to have a fire-resistance rating where sprinkler protection is extended to these areas.

    4. Where sprinkler protection is extended to the balcony areas, the aggregate length of the balcony on each floor shall not be limited.

    705.2.3.2 Vents. [SFM] Vents required by Section 2304.12.2.5 in fire-rated exterior balconies or elevated walkway surfaces shall be designed where the voids created at the intersection of the exterior curtain wall and the balcony floor are sealed with an approved material or system to retard the interior spread of flame, hot gases and products of combustion. Rated assemblies shall comply with Section 715. Ventilation openings shall comply with the fire sprinkler protection as required by Section 903.3.1.1 or 903.3.1.2 and the reference standard.

    705.2.4 Bay and oriel windows. Bay and oriel windows constructed of combustible materials shall conform to the type of construction required for the building to which they are attached.

    Exception: Fire-retardant-treated wood shall be permitted on buildings three stories or less above grade plane of Type I, II, III or IV construction.

  • CBC § 705.1 High relevance — show source text

    SECTION 705—EXTERIOR WALLS

    705.1 General. Exterior walls shall comply with this section.

    705.2 Projections. Cornices, eave overhangs, exterior balconies and similar projections extending beyond the exterior wall shall conform to the requirements of this section and Section 1405. Exterior egress balconies and exterior exit stairways and ramps shall comply with Sections 1021 and 1027, respectively. Projections shall not extend any closer to the line used to determine the fire separation distance than shown in Table 705.2.

    Exception: Buildings on the same lot and considered as portions of one building in accordance with Section 705.3 are not required to comply with this section for projections between the buildings.

    TABLE 705.2—MINIMUM DISTANCE OF PROJECTION Col2
    FIRE SEPARATION DISTANCE (FSD) (feet) MINIMUM DISTANCE FROM LINE USED TO DETERMINE FSD
    0 to less than 2 Projections not permitted
    2 to less than 3 24 inches
    3 to less than 5 Two-thirds of FSD
    5 or greater 40 inches
    For SI: 1 foot = 304.8 mm; 1 inch = 25.4 mm. For SI: 1 foot = 304.8 mm; 1 inch = 25.4 mm.

    705.2.1 Types I and II construction. Projections from walls of Type I or II construction shall be of noncombustible materials or combustible materials as allowed by Sections 705.2.3.1 and 705.2.4.

    705.2.2 Type III, IV or V construction. Projections from walls of Type III, IV or V construction shall be of any approved material.

    705.2.3 Projection protection. Projections extending to 5 feet (1524 mm) or less from the line used to determine the fire separation distance shall be one of the following:

    1. Noncombustible materials.

    2. Combustible materials of not less than 1-hour fire-resistance-rated construction.

    3. Heavy timber construction complying with Section 2304.11.

    4. Fire-retardant-treated wood.

    5. As permitted by Section 705.2.3.1.

    Exception: Type VB construction shall be allowed for combustible projections in Group R-3 and U occupancies with a fire separation distance greater than or equal to 5 feet (1524 mm).

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    FIRE AND SMOKE PROTECTION FEATURES

    705.2.3.1 Balconies and similar projections. Balconies and similar projections of combustible construction other than fireretardant-treated wood shall be fire-resistance rated where required by Table 601 for floor construction or shall be of heavy timber construction in accordance with Section 2304.11. The aggregate length of the projections shall not exceed 50 percent of the building’s perimeter on each floor.

  • CBC § 602.4.4.3 High relevance — show source text
    1. A noncombustible material.

    602.4.4.3 Concealed spaces. Concealed spaces shall not contain combustible materials other than building elements and electrical, mechanical, fire protection, or plumbing materials and equipment permitted in plenums in accordance with the California Mechanical Code . Concealed spaces shall comply with applicable provisions of Section 718. Concealed spaces shall be protected in accordance with one or more of the following:

    1. The building shall be sprinklered throughout in accordance with Section 903.3.1.1 and automatic sprinklers shall also be provided in the concealed space.
    2. The concealed space shall be completely filled with noncombustible insulation.

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    TYPES OF CONSTRUCTION

    1. Combustible surfaces within the concealed space shall be fully sheathed with not less than [5] / 8 -inch Type X gypsum board.

    Exception: Concealed spaces within interior walls and partitions with a 1-hour or greater fire-resistance rating complying with Section 2304.11.2.2 shall not require additional protection.

    602.4.4.4 Exterior structural members. Where a fire separation distance of 20 feet (6096 mm) or more is provided, wood columns and arches conforming to heavy timber sizes complying with Section 2304.11 shall be permitted to be used externally.

    602.5 Type V. Type V construction is that type of construction in which the structural elements, exterior walls and interior walls are of any materials permitted by this code.

    SECTION 603—COMBUSTIBLE MATERIAL IN TYPES I AND II CONSTRUCTION

    603.1 Allowable materials. Combustible materials shall be permitted in buildings of Type I or II construction in the following applications and in accordance with Sections 603.1.1 through 603.1.3:

    1. Fire-retardant-treated wood complying with Section 2303.2 shall be permitted in: 1.1. Nonbearing partitions where the required fire-resistance rating is 2 hours or less except in shaft enclosures within Group I-2 occupancies and ambulatory care facilities. 1.2. Nonbearing exterior walls where fire-resistance-rated construction is not required. 1.3. Roof construction, including girders, trusses, framing and decking. Exceptions:
    2. In buildings of Type IA construction exceeding two stories above grade plane, fire-retardant-treated wood is not permitted in roof construction where the vertical distance from the upper floor to the roof is less than 20 feet (6096 mm).
    3. Group I-2, roof construction containing fire-retardant-treated wood shall be covered by not less than a Class A roof covering or roof assembly, and the roof assembly shall have a fire-resistance rating where required by the construction type. 1.4. Balconies, porches, decks and exterior stairways not used as required exits on buildings three stories or less above grade plane.
    4. Thermal and acoustical insulation, other than foam plastics, having a flame spread index of not more than 25. Exceptions:
    5. Insulation placed between two layers of noncombustible materials without an intervening airspace shall be allowed to have a flame spread index of not more than 100.
    6. Insulation installed between a finished floor and solid decking without intervening airspace shall be allowed to have a flame spread index of not more than 200.
    7. Foam plastics in accordance with Chapter 26.
  • CBC § 1404.19 High relevance — show source text

    [BS] 1404.19 Fiber-mat reinforced cementitious backer units. Fiber-mat reinforced cementitious backer units shall be permitted on exterior walls and shall meet the requirements of Section 1404.19.1.

    [BS] 1404.19.1 Installation. Installation of fiber-mat reinforced cementitious backer units used as an exterior substrate for the application of exterior finish materials shall be in accordance with backer unit manufacturer’s installation instructions. Panels shall be installed using corrosion-resistant fasteners. Finish materials shall be installed in accordance with approved finish material manufacturer’s instructions.

    SECTION 1405—COMBUSTIBLE MATERIALS ON THE EXTERIOR SIDE OF EXTERIOR WALLS

    1405.1 Combustible exterior wall coverings. Combustible exterior wall coverings shall comply with this section.

    Exception: Plastics complying with Chapter 26.

    1405.1.1 Types I, II, III and IV-HT construction. On buildings of Types I, II, III and IV-HT construction, exterior wall coverings shall be permitted to be constructed of combustible materials, complying with the following limitations:

    1. Combustible exterior wall coverings shall not exceed 10 percent of an exterior wall surface area where the fire separation distance is 5 feet (1524 mm) or less.
    2. Combustible exterior wall coverings shall be limited to 40 feet (12 192 mm) in height above grade plane. Exceptions:
    3. Metal composite material (MCM) systems complying with Section 1406.
    4. Exterior insulation and finish systems (EIFS) complying with Section 1407.
    5. High-pressure decorative exterior-grade compact laminate (HPL) systems complying with Section 1408.
    6. Exterior wall coverings containing foam plastic insulation complying with Section 2603.
    7. Combustible exterior wall coverings constructed of fire-retardant-treated wood complying with Section 2303.2 for exterior installation shall not be limited in wall surface area where the fire separation distance is 5 feet (1524 mm) or less and shall be permitted up to 60 feet (18 288 mm) in height above grade plane regardless of the fire separation distance.
    8. Wood veneers shall comply with Section 1404.6.

    1405.1.1.1 Ignition resistance. Where permitted by Section 1405.1.1, combustible exterior wall coverings shall be tested in accordance with NFPA 268.

    Exceptions:

    1. Wood or wood-based products.
    2. Other combustible materials covered with an exterior weather covering, other than vinyl sidings, included in and complying with the thickness requirements of Table 1404.2.
    3. Aluminum having a minimum thickness of 0.019 inch (0.48 mm).

    1405.1.1.1.1 Fire separation 5 feet or less. Where installed on exterior walls having a fire separation distance of 5 feet (1524 mm) or less, combustible exterior wall coverings shall not exhibit sustained flaming as defined in NFPA 268.

  • CBC § 602.4.4.4 High relevance — show source text
    1. Heavy timber as permitted by Note c to Table 601 and Sections 602.4.4.4 and 705.2.3.1.
    2. Aggregates, component materials and admixtures as permitted by Section 703.2.1.2.
    3. Sprayed fire-resistive materials and intumescent fire-resistive materials, determined on the basis of fire resistance tests in accordance with Section 703.2 and installed in accordance with Sections 1705.15 and 1705.16, respectively.

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    TYPES OF CONSTRUCTION

    1. Materials used to protect penetrations in fire-resistance-rated assemblies in accordance with Section 714.
    2. Materials used to protect joints in fire-resistance-rated assemblies in accordance with Section 715.
    3. Materials allowed in the concealed spaces of buildings of Types I and II construction in accordance with Section 718.5.
    4. Materials exposed within plenums complying with the California Mechanical Code .
    5. Wall construction of freezers and coolers of less than 1,000 square feet (92.9 m [2] ), in size, lined on both sides with noncombustible materials and the building is protected throughout with an automatic sprinkler system in accordance with Section 903.3.1.1.
    6. Wood nailers for parapet flashing and roof cants.
    7. Vapor retarders as required by Section 1404.3.

    603.1.1 Ducts. The use of nonmetallic ducts shall be permitted where installed in accordance with the limitations of the California Mechanical Code .

    603.1.2 Piping and plumbing fixtures. The use of combustible piping materials and plumbing fixtures shall be permitted where installed in accordance with the limitations of the California Mechanical Code and the California Plumbing Code .

    603.1.3 Electrical. The use of electrical wiring methods with combustible insulation, tubing, raceways and related components shall be permitted where installed in accordance with the limitations of this code and the California Electrical Code.

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    CALIFORNIA BUILDING CODE – MATRIX ADOPTION TABLE

    CHAPTER 7 – FIRE AND SMOKE PROTECTION FEATURES

    (Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

  • CBC § 8-6 High relevance — show source text

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    INTERIOR FINISHES

    804.4.3 Group I-2 and Group I-3 occupancy floor surfaces. Interior floor finish and floor coverings occupied by inmates or patients whose personal liberties are restrained shall be noncombustible.

    Exception: Carpet or other floor covering materials may be used in areas protected by an automatic sprinkler system installed throughout in accordance with Section 903.3.1.1. Carpet or other floor coverings shall comply with the requirements of ASTM Stan- dard E648; the minimum critical radiant flux shall be not less than Class I and the specific optical density smoke rating shall not exceed 450 per ASTM E662. Carpeting and carpet padding shall be tested as a unit in accordance with floor covering radiant panel test meeting class 1 and has a critical radiant flux limit of not less than 0.45 watt per centimeter square. The carpeting and padding shall be identified by a hang-tag or other suitable method as to manufacturer and style and shall indicate the classifica- tion of the material based on the limits set forth above.

    SECTION 805—COMBUSTIBLE MATERIALS IN TYPES I AND II CONSTRUCTION

    805.1 Application. Combustible materials installed on or embedded in floors of buildings of Type I or II construction shall comply with Sections 805.1.1 through 805.1.3.

    Exception: Stages and platforms constructed in accordance with Sections 410.2 and 410.3, respectively.

    805.1.1 Subfloor construction. Floor sleepers, bucks and nailing blocks shall not be constructed of combustible materials, unless the space between the fire-resistance-rated floor assembly and the flooring is either solidly filled with noncombustible materials or fireblocked in accordance with Section 718, and provided that such open spaces shall not extend under or through permanent partitions or walls.

    805.1.2 Wood finish flooring. Wood finish flooring is permitted to be attached directly to the embedded or fireblocked wood sleepers and shall be permitted where cemented directly to the top surface of fire-resistance-rated floor assemblies or directly to a wood subfloor attached to sleepers as provided for in Section 805.1.1. 805.1.3 Insulating boards. Combustible insulating boards not more than [1] / 2 inch (12.7 mm) thick and covered with finish flooring are permitted where attached directly to a noncombustible floor assembly or to wood subflooring attached to sleepers as provided for in Section 805.1.1.

    SECTION 806—DECORATIVE MATERIALS AND TRIM

    [F] 806.1 General. The following requirements shall apply to all occupancies:

    1. Furnishings or decorative materials of an explosive or highly flammable character shall not be used.

    2. Fire-retardant coatings in existing buildings shall be maintained so as to retain the effectiveness of the treatment under service conditions encountered in actual use.

    3. Furnishings or other objects shall not be placed to obstruct exits, access thereto, egress therefrom or visibility thereof.

    4. The permissible amount of decorative vegetation and noncombustible decorative materials shall not be limited.

  • CBC § 804.4 High relevance — show source text

    804.4 Interior floor finish requirements. Interior floor covering materials shall comply with Sections 804.4.1 and 804.4.2 and interior floor finish materials shall comply with Section 804.4.3 .

    804.4.1 Test requirement. In all occupancies, interior floor finish and interior floor covering materials shall comply with the requirements of the ASTM Standard E648, and having a specific optical density smoke rating not to exceed 450 per ASTM E662. For Group I-3 occupancies and Group I-2 areas where patients are restrained, see Section 804.4.3.

    804.4.2 Minimum critical radiant flux. In all occupancies, interior floor finish and floor covering materials in enclosures for stairways and ramps, exit passageways, corridors and rooms or spaces not separated from corridors by partitions extending from the floor to the underside of the ceiling shall withstand a minimum critical radiant flux. The minimum critical radiant flux shall be not less than Class I in Groups I-2 and I-3 areas where restraint is not used and R-2.1 and not less than Class II in Groups A, B, E, H, I-4, M, R-1, R-2, R-2.2 and S . For Group I-3 areas occupied by inmates or Group I-2 areas where patients are restrained, see Section 804.4.3.

    Exception: Where a building is equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1 or 903.3.1.2, Class II materials are permitted in any area where Class I materials are required, and materials complying with ASTM Standard E648, and having a specific optical density smoke rating not to exceed 450 per ASTM E662 are permitted in any area where Class II materials are required.

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    INTERIOR FINISHES

    804.4.3 Group I-2 and Group I-3 occupancy floor surfaces. Interior floor finish and floor coverings occupied by inmates or patients whose personal liberties are restrained shall be noncombustible.

    Exception: Carpet or other floor covering materials may be used in areas protected by an automatic sprinkler system installed throughout in accordance with Section 903.3.1.1. Carpet or other floor coverings shall comply with the requirements of ASTM Stan- dard E648; the minimum critical radiant flux shall be not less than Class I and the specific optical density smoke rating shall not exceed 450 per ASTM E662. Carpeting and carpet padding shall be tested as a unit in accordance with floor covering radiant panel test meeting class 1 and has a critical radiant flux limit of not less than 0.45 watt per centimeter square. The carpeting and padding shall be identified by a hang-tag or other suitable method as to manufacturer and style and shall indicate the classifica- tion of the material based on the limits set forth above.

    SECTION 805—COMBUSTIBLE MATERIALS IN TYPES I AND II CONSTRUCTION

    805.1 Application. Combustible materials installed on or embedded in floors of buildings of Type I or II construction shall comply with Sections 805.1.1 through 805.1.3.

    Exception: Stages and platforms constructed in accordance with Sections 410.2 and 410.3, respectively.

  • CBC § 705.2.3.2 High relevance — show source text

    Exceptions:

    1. On buildings of Types I and II construction, three stories or less above grade plane, fire-retardant-treated wood shall be permitted for balconies, porches, decks and exterior stairways not used as required exits.

    2. Untreated wood and plastic composites that comply with ASTM D7032 and Section 2612 are permitted for pickets, rails and similar guard components that are limited to 42 inches (1067 mm) in height.

    3. Balconies and similar projections on buildings of Types III, IV-HT and V construction shall be permitted to be of Type V construction and shall not be required to have a fire-resistance rating where sprinkler protection is extended to these areas.

    4. Where sprinkler protection is extended to the balcony areas, the aggregate length of the balcony on each floor shall not be limited.

    705.2.3.2 Vents. [SFM] Vents required by Section 2304.12.2.5 in fire-rated exterior balconies or elevated walkway surfaces shall be designed where the voids created at the intersection of the exterior curtain wall and the balcony floor are sealed with an approved material or system to retard the interior spread of flame, hot gases and products of combustion. Rated assemblies shall comply with Section 715. Ventilation openings shall comply with the fire sprinkler protection as required by Section 903.3.1.1 or 903.3.1.2 and the reference standard.

    705.2.4 Bay and oriel windows. Bay and oriel windows constructed of combustible materials shall conform to the type of construction required for the building to which they are attached.

    Exception: Fire-retardant-treated wood shall be permitted on buildings three stories or less above grade plane of Type I, II, III or IV construction.

    705.3 Buildings on the same lot. For the purposes of determining the required wall and opening protection, projections and roofcovering requirements, buildings on the same lot shall be assumed to have an imaginary line between them.

    Where a new building is to be erected on the same lot as an existing building, the location of the assumed imaginary line with relation to the existing building shall be such that the exterior wall and opening protection of the existing building meet the criteria as set forth in Sections 705.5 and 705.9.

    Exceptions:

    1. Two or more buildings on the same lot shall be either regulated as separate buildings or shall be considered as portions of one building if the aggregate area of such buildings is within the limits specified in Chapter 5 for a single building. Where the buildings contain different occupancy groups or are of different types of construction, the area shall be that allowed for the most restrictive occupancy or construction.
    2. Where an S-2 parking garage of Construction Type I or IIA is erected on the same lot as a Group R-2 building, and there is no fire separation distance between these buildings, then the adjoining exterior walls between the buildings are permitted to have occupant use openings in accordance with Section 706.8. However, opening protectives in such openings shall only be required in the exterior wall of the S-2 parking garage, not in the exterior wall openings in the R-2 building, and these opening protectives in the exterior wall of the S-2 parking garage shall be not less than 1 [1] / 2 -hour fire protection rating.

    705.4 Materials. Exterior walls shall be of materials permitted by the building’s type of construction.

  • CBC § 14-15 High relevance — show source text

    2025 CALIFORNIA BUILDING CODE 14-15

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

    EXTERIOR WALLS

    [BS] 1404.18 Polypropylene siding. Polypropylene siding conforming to the requirements of this section and complying with Section 1403.11 shall be limited to exterior walls located in areas where the basic wind speed, V, specified in Chapter 16 does not exceed 100 miles per hour (45 m/s) and the building height is less than or equal to 40 feet (12 192 mm) in Exposure C. Where construction is located in areas where the basic wind speed, V, exceeds 100 miles per hour (45 m/s), or building heights are in excess of 40 feet (12 192 mm), tests or calculations indicating compliance with Chapter 16 shall be submitted.

    [BS] 1404.18.1 Installation. Polypropylene siding and accessories shall be installed over and attached to wood structural panel sheathing with nailable substrate not less than [7] / 16 inch (11.1 mm) in thickness or other substrate suitable for mechanical fasteners in accordance with the approved manufacturer’s instructions.

    [BS] 1404.18.2 Fastener requirements. Unless otherwise specified in the approved manufacturer’s instructions, nails shall be corrosion resistant, with a minimum 0.120-inch (3 mm) shank and a minimum 0.313-inch (8 mm) head diameter. Nails shall be not less than 1 [1] / 4 inches (32 mm) long or as necessary to penetrate sheathing or nailable substrate not less than [3] / 4 inch (19.1 mm). Where the nail fully penetrates the sheathing or nailable substrate, the end of the fastener shall extend not less than [1] / 4 inch (6.4 mm) beyond the opposite face of the sheathing or nailable substrate. Spacing of fasteners shall be installed in accordance with the approved manufacturer’s instructions.

    [BS] 1404.19 Fiber-mat reinforced cementitious backer units. Fiber-mat reinforced cementitious backer units shall be permitted on exterior walls and shall meet the requirements of Section 1404.19.1.

    [BS] 1404.19.1 Installation. Installation of fiber-mat reinforced cementitious backer units used as an exterior substrate for the application of exterior finish materials shall be in accordance with backer unit manufacturer’s installation instructions. Panels shall be installed using corrosion-resistant fasteners. Finish materials shall be installed in accordance with approved finish material manufacturer’s instructions.

    SECTION 1405—COMBUSTIBLE MATERIALS ON THE EXTERIOR SIDE OF EXTERIOR WALLS

    1405.1 Combustible exterior wall coverings. Combustible exterior wall coverings shall comply with this section.

    Exception: Plastics complying with Chapter 26.

    1405.1.1 Types I, II, III and IV-HT construction. On buildings of Types I, II, III and IV-HT construction, exterior wall coverings shall be permitted to be constructed of combustible materials, complying with the following limitations:

    1. Combustible exterior wall coverings shall not exceed 10 percent of an exterior wall surface area where the fire separation distance is 5 feet (1524 mm) or less.
    2. Combustible exterior wall coverings shall be limited to 40 feet (12 192 mm) in height above grade plane. Exceptions:
  • CBC § 602.1.1 High relevance — show source text

    3.2. The distance between solar photovoltaic array structures is a minimum of 10 feet clear. 3.3. The driveway aisle separating solar photovoltaic array structures has a minimum width of 25 feet clear. 3.4. Solar photovoltaic array structure is used only for parking purposes with no storage. 3.5. Completely open on all sides (other than necessary structural supports) with no interior partitions.

    602.1.1 Minimum requirements. A building or portion thereof shall not be required to conform to the details of a type of construction higher than that type which meets the minimum requirements based on occupancy even though certain features of such a building actually conform to a higher type of construction.

    602.2 Types I and II. Types I and II construction are those types of construction in which the building elements specified in Table 601 are of noncombustible materials, except as permitted in Section 603 and elsewhere in this code.

    602.3 Type III. Type III construction is that type of construction in which the exterior walls are of noncombustible materials and the interior building elements are of any material permitted by this code. Fire-retardant-treated wood framing and sheathing complying with Section 2303.2 shall be permitted within exterior wall assemblies of a 2-hour rating or less.

    602.4 Type IV. Type IV construction is that type of construction in which the building elements are mass timber or noncombustible materials and have fire-resistance ratings in accordance with Table 601. Mass timber elements shall meet the fire-resistance-rating requirements of this section based on either the fire-resistance rating of the noncombustible protection, the mass timber, or a combination of both and shall be determined in accordance with Section 703.2. The minimum dimensions and permitted materials for building elements shall comply with the provisions of this section and Section 2304.11. Mass timber elements of Types IV-A, IV-B and IV-C construction shall be protected with noncombustible protection applied directly to the mass timber in accordance with Sections 602.4.1 through 602.4.3. The time assigned to the noncombustible protection shall be determined in accordance with Section 703.6 and comply with Section 722.7.

    Cross-laminated timber shall be labeled as conforming to ANSI/APA PRG 320 as referenced in Section 2303.1.4.

    Exterior load-bearing walls and nonload-bearing walls shall be mass timber construction, or shall be of noncombustible construction.

    Exception: Exterior load-bearing walls and nonload-bearing walls of Type IV-HT Construction in accordance with Section 602.4.4.

    The interior building elements, including nonload-bearing walls and partitions, shall be of mass timber construction or of noncombustible construction.

    Exception: Interior building elements and nonload-bearing walls and partitions of Type IV-HT construction in accordance with Section 602.4.4.

    Combustible concealed spaces are not permitted except as otherwise indicated in Sections 602.4.1 through 602.4.4. Combustible stud spaces within light frame walls of Type IV-HT construction shall not be considered concealed spaces, but shall comply with Section 718.

  • CBC § 806.6. High relevance — show source text

    1. Roof coverings that have an A, B or C classification.

    2. Interior floor finish and floor covering materials installed in accordance with Section 804.

    3. Millwork such as doors, door frames, window sashes and frames.

    4. Interior wall and ceiling finishes installed in accordance with Section 803.

    5. Trim installed in accordance with Section 806.6.

    6. Where not installed greater than 15 feet (4572 mm) above grade, show windows, nailing or furring strips and wooden bulkheads below show windows, including their frames, aprons and show cases.

    7. Finish flooring installed in accordance with Section 805.

    8. Partitions dividing portions of stores, offices or similar places occupied by one tenant only and that do not establish a corridor serving an occupant load of 30 or more shall be permitted to be constructed of fire-retardant-treated wood complying with Section 2303.2, 1-hour fire-resistance-rated construction or of wood panels or similar light construction up to 6 feet (1829 mm) in height.

    9. Stages and platforms constructed in accordance with Sections 410.2 and 410.3, respectively.

    10. Combustible exterior wall coverings, balconies and similar projections and bay or oriel windows in accordance with Chapter 14 and Section 705.2.3.1.

    11. Blocking such as for handrails, millwork, cabinets and window and door frames.

    12. Light-transmitting plastics as permitted by Chapter 26.

    13. Mastics and caulking materials applied to provide flexible seals between components of exterior wall construction.

    14. Exterior plastic veneer installed in accordance with Section 2605.2.

    15. Nailing or furring strips as permitted by Section 803.15.

    16. Heavy timber as permitted by Note c to Table 601 and Sections 602.4.4.4 and 705.2.3.1.

    17. Aggregates, component materials and admixtures as permitted by Section 703.2.1.2.

    18. Sprayed fire-resistive materials and intumescent fire-resistive materials, determined on the basis of fire resistance tests in accordance with Section 703.2 and installed in accordance with Sections 1705.15 and 1705.16, respectively.

    2025 CALIFORNIA BUILDING CODE 6-7

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

    �

    TYPES OF CONSTRUCTION

    1. Materials used to protect penetrations in fire-resistance-rated assemblies in accordance with Section 714.
    2. Materials used to protect joints in fire-resistance-rated assemblies in accordance with Section 715.
    3. Materials allowed in the concealed spaces of buildings of Types I and II construction in accordance with Section 718.5.
    4. Materials exposed within plenums complying with the California Mechanical Code .
    5. Wall construction of freezers and coolers of less than 1,000 square feet (92.9 m [2] ), in size, lined on both sides with noncombustible materials and the building is protected throughout with an automatic sprinkler system in accordance with Section 903.3.1.1.
    6. Wood nailers for parapet flashing and roof cants.
    7. Vapor retarders as required by Section 1404.3.

    603.1.1 Ducts. The use of nonmetallic ducts shall be permitted where installed in accordance with the limitations of the California Mechanical Code .

  • CBC § 718.4 High relevance — show source text

    718.4 Draftstops in attics. Draftstops shall be installed to subdivide attic spaces where required by Section 708.4.3. In other than Group R, draftstops shall be installed to subdivide combustible attic spaces and combustible concealed roof spaces such that any horizontal area does not exceed 3,000 square feet (279 m [2] ). Ventilation of concealed roof spaces shall be maintained in accordance with Section 1202.2.1.

    Exception: Buildings equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1.

    718.4.1 Draftstops material. Materials utilized for draftstops of attic spaces shall comply with Section 718.3.1.

    718.4.1.1 Openings. Openings in the partitions shall be protected by self-closing doors with automatic latches constructed as required for the partitions.

    718.5 Combustible materials in concealed spaces in Type I or II construction. Combustible materials shall not be permitted in concealed spaces of buildings of Type I or II construction.

    Exceptions:

    1. Combustible materials in accordance with Section 603.

    2. Combustible materials exposed within plenums complying with the California Mechanical Code .

    3. Class A interior finish materials classified in accordance with Section 803.

    2025 CALIFORNIA BUILDING CODE 7-41

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

    FIRE AND SMOKE PROTECTION FEATURES

    1. Combustible piping within partitions or shaft enclosures installed in accordance with the provisions of this code.
    2. Combustible piping within concealed ceiling spaces installed in accordance with the California Mechanical Code and the California Plumbing Code .
    3. Combustible insulation and covering on pipe and tubing, installed in concealed spaces other than plenums, complying with Section 720.7.

    SECTION 719—FIRE-RESISTANCE REQUIREMENTS FOR PLASTER

    719.1 Thickness of plaster. The minimum thickness of gypsum plaster or Portland cement plaster used in a fire-resistance-rated system shall be determined by the prescribed fire tests. The plaster thickness shall be measured from the face of the lath where applied to gypsum lath or metal lath. 719.2 Plaster equivalents. For fire-resistance purposes, [1] / 2 inch (12.7 mm) of unsanded gypsum plaster shall be deemed equivalent to [3] / 4 inch (19.1 mm) of one-to-three gypsum sand plaster or 1 inch (25 mm) of Portland cement sand plaster.

    719.3 Noncombustible furring. In buildings of Types I and II construction, plaster shall be applied directly on concrete or masonry or on approved noncombustible plastering base and furring.

    719.4 Double reinforcement. Plaster protection more than 1 inch (25 mm) in thickness shall be reinforced with an additional layer of approved lath embedded not less than [3] / 4 inch (19.1 mm) from the outer surface and fixed securely in place.

    Exception: Solid plaster partitions or where otherwise determined by fire tests.

Frequently asked questions

Can I use plain (untreated) wood for partitions in a Type I building?

No. Untreated wood is not freely permitted in Type I/II building elements except where specifically listed. Fire‑retardant‑treated wood is permitted in certain nonbearing partitions when the required fire‑resistance rating is 2 hours or less per § 603.1, but untreated wood is not an allowed general substitute.

Are nonmetallic ducts banned in Type I and II buildings?

No — nonmetallic ducts are permitted, but only when they are installed in accordance with the limitations of the California Mechanical Code (see § 603.1.1). Check the Mechanical Code for material, listing and installation restrictions.

Can I use foam plastic insulation in walls of a Type I building?

Not under the general insulation allowance. Foam plastics are regulated separately (Chapter 26); do not assume the § 603 insulation flame‑spread allowances apply to foam plastics. Consult Chapter 26 and § 603.1 for the correct path.

Does § 603 allow combustible materials in concealed roof or attic spaces?

Generally combustible materials are not permitted in concealed spaces of Type I/II buildings; exceptions exist that reference § 603 and other provisions (see § 718.5). Sprinkler protection, noncombustible insulation fill, or other specified protections may be required.

If electrical wiring uses combustible insulation, is that a code violation in Type I/II?

Not automatically. § 603.1.3 permits electrical wiring methods with combustible insulation provided the installation complies with this code and the California Electrical Code — you must meet the referenced electrical code requirements.

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