CBC · California Building Code

What are the area limits and flame‑spread requirements for interior trim?

Trim (molding, chair rails, picture rails, etc.) may cover up to 10% of the wall or ceiling where it’s installed. Non‑foam trim must meet occupancy‑based flame‑spread classes (see §806.6) and foam trim must meet the density, size and flame‑spread limits in §2604.2 (density ≥20 pcf, ≤1/2" thick, ≤8" wide, flame spread ≤75). If the material has NFPA 286 interior‑finish test data that meets §803.1.1.1, that testing can be used instead of the ASTM E84/UL 723 tunnel test.

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Last reviewed: July 5, 2026

What the code requires — 2–4 sentences

Interior trim (molding, picture rails, chair rails, decorative trim, etc.) is limited to no more than 10 percent of the specific wall or ceiling area to which it is attached, whether combustible or foam plastic. Non‑foam trim must meet the flame‑spread/smoke requirements specified for its occupancy in §806.6, and foam‑plastic trim must meet the density, size, area and flame‑spread limits in §2604.2 (or alternatively be tested as interior finish per NFPA 286). See §806.6 for non‑foam trim requirements and §2604.2 for foam plastic trim requirements .

Requirements in detail

Applicability

  • “Interior trim” in these sections is trim attached to walls or ceilings and expressly excludes handrails and guardrails when applying the 10% cap. The trim rules in Chapter 8 (interior finishes/trim) apply to both new and existing buildings where Chapter 8 is enforced; foam plastics have their own specific limits in Chapter 26 (§2604.2) .

Key numeric limits and classifications

Requirement Value / limit Code Reference
Maximum percent of a specific wall or ceiling area that may be combustible trim (excl. handrails/guardrails) 10% §806.6
Non‑foam trim flame/smoke requirement — Group I‑3 (minimum) Minimum Class B flame spread; smoke‑developed index 450 §806.6
Non‑foam trim flame/smoke requirement — all other occupancies Class C flame spread and smoke‑developed index (minimum) §806.6
Foam plastic trim — minimum density 20 pcf (320 kg/m3) §2604.2.1
Foam plastic trim — maximum thickness 1/2 inch (12.7 mm) §2604.2.2
Foam plastic trim — maximum width 8 inches (204 mm) §2604.2.2
Foam plastic trim — area limitation Trim shall not constitute more than 10% of the specific wall or ceiling area to which it is attached §2604.2.3
Foam plastic trim — flame spread (ASTM E84 / UL 723) Flame‑spread index ≤ 75; smoke‑developed index not limited (unless other provisions apply) §2604.2.4
Alternative compliance for any trim If tested as interior finish per NFPA 286 and meeting §803.1.1.1 acceptance criteria, the trim is not required to be tested to ASTM E84/UL 723 (NFPA 286 acceptance supersedes the ASTM E84 requirement) §2604.2 Exception and §803.1.1.1

Notes on classes: Chapter 8 groups finish materials by flame spread and smoke indexes (Class A/B/C per ASTM E84). See §803.1.2 for the numeric ranges for Class A, B and C (Class A = 0–25, B = 26–75, C = 76–200) .

Testing and standards

  • ASTM E84 or UL 723 are the referenced tunnel tests for establishing flame‑spread and smoke‑developed indices when the code requires those metrics. Where NFPA 286 testing has been performed and meets the acceptance criteria in §803.1.1.1, NFPA 286 can be used instead of ASTM E84/UL 723 for interior trim acceptance .

Exceptions & special cases

  • NFPA 286 alternate test: If the trim material (foam or other) has been tested as an interior finish under NFPA 286 and meets the acceptance criteria of §803.1.1.1, it need not also be tested by ASTM E84 / UL 723 for flame spread index requirements. This is specifically noted as an exception for foam trim in §2604.2 and for interior trim generally in Chapter 8 .
  • Handrails and guardrails are excluded from the 10% combustible‑trim area limitation (they are treated separately) per §806.6 .
  • Plenums and other special HVAC spaces: foam plastics installed in plenums have much stricter requirements (see §2603.7) and in some cases must meet a flame spread index of 25 and smoke index 50 unless separated by an approved thermal barrier; if trim is in a plenum, follow the plenum rules in addition to §2604.2 .
  • Group I‑3 occupancy: non‑foam trim requires the higher performance (minimum Class B) in I‑3 occupancies per §806.6 .

Common mistakes

  • Treating the 10% limit as a room‑wide aggregate for all walls and ceilings without checking the phrase “specific wall or ceiling area”: the code limits trim to 10% of the specific wall or ceiling area to which it is attached (apply the percentage to the area of the wall/ceiling where the trim is installed) §806.6 and §2604.2.3 .
  • Assuming any foam is allowed if thin: foam plastic trim still must meet density, size and flame spread limits in §2604.2; thickness alone isn’t the only criterion .
  • Confusing interior finish and interior trim testing paths: if a material has NFPA 286 interior‑finish test data meeting §803.1.1.1, it may be accepted without ASTM E84 data; but absent that test the ASTM E84/UL 723 or the class requirements in §806.6/§2604.2 apply .
  • Forgetting occupancy differences: Group I‑3 requires higher performance for non‑foam trim (Class B) while most other occupancies permit Class C. Verify occupancy classification before selecting materials .
  • Overlooking plume/plenum rules: foam in plenums is subject to §2603.7 and may need far stricter flame/smoke performance than ordinary trim in occupied spaces .

Worked example — concrete scenario

Scenario: You are installing decorative foam crown molding around a single classroom wall that is 30 ft long by 10 ft high (wall area = 300 ft²). The foam molding pieces are 6 in (0.5 ft) wide by 0.5 in (0.0417 ft) thick, density 22 pcf, tested ASTM E84 with flame‑spread index 70.

Step 1 — Area limit:

  • The code caps interior trim at 10% of the specific wall area where attached. For the 300 ft² wall, 10% = 30 ft².
  • Your trim area = (wall length × trim width). If the trim runs the full 30 ft length and is 0.5 ft wide, trim area = 30 ft × 0.5 ft = 15 ft² → 15/300 = 5% ⇒ within the 10% cap (OK) per §2604.2.3 and §806.6 .

Step 2 — Foam properties and flame spread:

  • Density = 22 pcf (≥ 20 pcf required) → OK per §2604.2.1.
  • Thickness = 0.5 in (meets maximum 1/2 in) and width 6 in (≤ 8 in) → OK per §2604.2.2.
  • Flame‑spread index = 70 (≤ 75 required for foam trim under ASTM E84) → OK per §2604.2.4.

Conclusion: The molding as described complies with foam trim requirements (dimension/density/area/flame spread) in §2604.2, provided the occupancy doesn’t impose a more stringent condition (e.g., plenum or a special occupancy) and provided NFPA 286 is not required or otherwise used to demonstrate equivalency .

Related provisions

  • §803.1.2 — Classification ranges and testing (ASTM E84 / UL 723) for interior finishes and the numeric bands for Class A/B/C .
  • §803.1.1.1 — NFPA 286 acceptance criteria (alternate large‑scale test acceptance) .
  • §2603.7 — Foam plastic in plenums: stricter flame‑ and smoke‑index requirements and testing criteria .
  • §2603.9 — Special approval pathways and large‑scale tests (NFPA 286, FM 4880, UL 1040, UL 1715) for foam plastics used as interior finish/trim assemblies .
  • §806.7 — Requirements for interior floor‑wall base (height limit and testing) and the exception referencing §806.6 .

Code references

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

  • CBC § 2604.1 High relevance — show source text

    SECTION 2604—INTERIOR FINISH AND TRIM

    2604.1 General. Plastic materials installed as interior finish or trim shall comply with Chapter 8. Foam plastics shall only be installed as interior finish where approved in accordance with the special provisions of Section 2603.9. Foam plastics that are used as interior finish shall meet the flame spread and smoke-developed index requirements for interior finish in accordance with Chapter 8. Foam plastics installed as interior trim shall comply with Section 2604.2. 2604.1.1 Plenums. Foam plastics installed in plenums as interior wall or ceiling finish shall comply with Section 2603.7. Foam plastics installed in plenums as interior trim shall comply with Sections 2604.2 and 2603.7.

    [F] 2604.2 Interior trim. Foam plastic used as interior trim shall comply with Sections 2604.2.1 through 2604.2.4.

    [F] 2604.2.1 Density. The minimum density of the interior trim shall be 20 pcf (320 kg/m [3] ).

    [F] 2604.2.2 Thickness. The maximum thickness of the interior trim shall be [1] / 2 inch (12.7 mm) and the maximum width shall be 8 inches (204 mm).

    [F] 2604.2.3 Area limitation. The interior trim shall not constitute more than 10 percent of the specific wall or ceiling areas to which it is attached.

    [F] 2604.2.4 Flame spread. The flame spread index shall not exceed 75 where tested in accordance with ASTM E84 or UL 723. The smoke-developed index shall not be limited.

    Exception: Where the interior trim material has been tested as an interior finish in accordance with NFPA 286 and complies with the acceptance criteria in Section 803.1.1.1, it shall not be required to be tested for flame spread index in accordance with ASTM E84 or UL 723.

    2025 CALIFORNIA BUILDING CODE 26-7

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    PLASTIC

    SECTION 2605—PLASTIC VENEER

    2605.1 Interior use. Where used within a building, plastic veneer shall comply with the interior finish requirements of Chapter 8.

    2605.2 Exterior use. Exterior plastic veneer, other than plastic siding, shall be permitted to be installed on the exterior walls of buildings of any type of construction in accordance with all of the following requirements:

    1. Plastic veneer shall comply with Section 2606.4.
    2. Plastic veneer shall not be attached to any exterior wall to a height greater than 50 feet (15 240 mm) above grade.
    3. Sections of plastic veneer shall not exceed 300 square feet (27.9 m [2] ) in area and shall be separated by not less than 4 feet (1219 mm) vertically.

    Exception: The area and separation requirements and the smoke-density limitation are not applicable to plastic veneer applied to buildings constructed of Type VB construction, provided that the walls are not required to have a fire-resistance rating.

    2605.3 Plastic siding. Plastic siding shall comply with the requirements of Sections 1403 and 1404.

    SECTION 2606—LIGHT-TRANSMITTING PLASTICS

  • CBC § 804.1.1 High relevance — show source text

    804.1.1 Testing in accordance with NFPA 286. Interior trim material shall be tested in accordance with NFPA 286 and comply with the acceptance criteria in Section 803.1.1.1. Where the interior trim material has been tested as an interior finish in accordance with NFPA 286 and complies with the acceptance criteria in Section 803.1.1.1, it shall not be required to be tested for flame spread index and smoke-developed index in accordance with ASTM E84 or UL 723.

    804.1.2 Testing in accordance with ASTM E84 or UL 723. Material, other than foam plastic, used as interior trim shall have minimum Class C flame spread and smoke-developed indices, when tested in accordance with ASTM E84 or UL 723, as described in Section 803.1.2.

    804.2 Foam plastic interior trim. Foam plastic used as interior trim shall comply with Sections 804.2.1 through 804.2.4. 804.2.1 Density. The minimum density of the interior trim shall be 20 pounds per cubic foot (320 kg/m [3] ). 804.2.2 Thickness. The maximum thickness of the interior trim shall be [1] / 2 inch (12.7 mm) and the maximum width shall be 8 inches (203 mm).

    804.2.3 Area limitation. The interior trim shall not constitute more than 10 percent of the specific wall or ceiling area to which it is attached.

    804.2.4 Flame spread. The flame spread index shall not exceed 75 where tested in accordance with ASTM E84 or UL 723. The smoke-developed index shall not be limited.

    Exception: Where the interior trim material has been tested as an interior finish in accordance with NFPA 286 and complies with the acceptance criteria in Section 803.1.1.1, it is not required to be tested for flame spread index in accordance with ASTM E84 or UL 723.

    804.3 New interior floor finish. New interior floor finish and floor covering materials in new and existing buildings shall comply with Sections 804.3.1 through 804.3.3.2.

    Exception: Floor finishes and coverings of a traditional type, such as wood, vinyl, linoleum or terrazzo, and resilient floor covering materials that are not composed of fibers.

    804.3.1 Classification. Interior floor finish and floor covering materials required by Section 804.3.3.2 to be of Class I or II materials shall be classified in accordance with ASTM E648 or NFPA 253. The classification referred to herein corresponds to the classifications determined by ASTM E648 or NFPA 253 as follows: Class I, 0.45 watts/cm [2] or greater; Class II, 0.22 watts/cm [2] or greater.

    804.3.2 Testing and identification. Interior floor finish and floor covering materials shall be tested by an approved agency in accordance with ASTM E648 or NFPA 253 and identified by a hang tag or other suitable method so as to identify the manufacturer or supplier and style, and shall indicate the interior floor finish or floor covering classification in accordance with Section 804.3.1. Carpet-type floor coverings shall be tested as proposed for use, including underlayment. Test reports confirming the information provided in the manufacturer’s product identification shall be furnished to the fire code official upon request.

  • CBC § 806.4 High relevance — show source text

    [F] 806.4 Acceptance criteria and reports. Where required to exhibit improved fire performance, curtains, draperies, fabric hangings and similar combustible decorative materials suspended from walls or ceilings shall be tested by an approved agency and shall be flame resistant in accordance with the provisions set forth in CCR, Title 19, Division 1, Chapter 8 . Reports of test results shall be prepared in accordance with the test method used and furnished to the building official on request.

    2025 CALIFORNIA BUILDING CODE 8-7

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    INTERIOR FINISHES

    [F] 806.5 Pyroxylin plastic. Imitation leather or other material consisting of or coated with a pyroxylin or similarly hazardous base shall not be used in Group A occupancies.

    [F] 806.6 Interior trim. Material, other than foam plastic used as interior trim, shall have a minimum Class B flame spread and 450 smoke-developed index in Group I-3 and for all other occupancies Class C flame spread and smoke-developed index when tested in accordance with ASTM E84 or UL 723, as described in Section 803.1.2. Combustible trim, excluding handrails and guardrails, shall not exceed 10 percent of the specific wall or ceiling area to which it is attached.

    [F] 806.6.1 Foam plastic. Foam plastic used as interior trim in any occupancy shall comply with Section 2604.2.

    [F] 806.7 Interior floor-wall base. Interior floor-wall base that is 6 inches (152 mm) or less in height shall be tested in accordance with Section 804.2 and shall be not less than Class II. Where a Class I floor finish is required, the floor-wall base shall be Class I.

    Exception: Interior trim materials that comply with Section 806.6.

    [F] 806.8 Combustible lockers. Where lockers constructed of combustible materials are used, the lockers shall be considered to be interior finish and shall comply with Section 803.

    Exception: Lockers constructed entirely of wood and noncombustible materials shall be permitted to be used wherever interior finish materials are required to meet a Class C classification in accordance with Section 803.1.2.

    SECTION 807—INSULATION

    807.1 Insulation. Thermal and acoustical insulation shall comply with Section 720.

    SECTION 808—ACOUSTICAL CEILING SYSTEMS

    808.1 Acoustical ceiling systems. The quality, design, fabrication and erection of metal suspension systems for acoustical tile and lay-in panel ceilings in buildings or structures shall conform to generally accepted engineering practice, the provisions of this chapter and other applicable requirements of this code.

    808.1.1 Materials and installation. Acoustical materials complying with the interior finish requirements of Section 803 shall be installed in accordance with the manufacturer’s recommendations and applicable provisions for applying interior finish.

    808.1.1.1 Suspended acoustical ceilings. Suspended acoustical ceiling systems shall be installed in accordance with the provisions of ASTM C635 and ASTM C636.

    808.1.1.2 Fire-resistance-rated construction. Acoustical ceiling systems that are part of fire-resistance-rated construction shall be installed in the same manner used in the assembly tested and shall comply with the provisions of Chapter 7.

  • CBC § 5.6 High relevance — show source text

    R303.5.6 Foam-filled garage doors. Foam-filled garage doors in attached or detached garages are exempt from the requirements of Sections R303.3 and R303.4.

    3-32 2025 CALIFORNIA RESIDENTIAL CODE

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    BUILDING PLANNING

    R303.5.7 Foam backer board. The thermal barrier specified in Section R303.4 is not required where siding backer board foam plastic insulation has a thickness of not more than 0.5 inch (12.7 mm) and a potential heat of not more than 2000 Btu per square foot (22 720 kJ/m [2] ) when tested in accordance with NFPA 259 and it complies with one or more of the following:

    1. The foam plastic insulation is separated from the interior of the building by not less than 2 inches (51 mm) of mineral fiber insulation.

    2. The foam plastic insulation is installed over existing exterior wall finish in conjunction with re-siding.

    3. The foam plastic insulation has been tested in accordance with Section R303.6.

    R303.5.8 Re-siding. The thermal barrier specified in Section R303.4 is not required where the foam plastic insulation is installed over existing exterior wall finish in conjunction with re-siding provided that the foam plastic has a thickness of not more than 0.5 inch (12.7 mm) and a potential heat of not more than 2000 Btu per square foot (22 720 kJ/m [2] ) when tested in accordance with NFPA 259.

    R303.5.9 Interior trim. The thermal barrier specified in Section R303.4 is not required for exposed foam plastic interior trim, provided that all of the following are met:

    1. The density is not less than 20 pounds per cubic foot (320 kg/m [3] ).
    2. The thickness of the trim is not more than 0.5 inch (12.7 mm) and the width is not more than 8 inches (204 mm).
    3. The interior trim shall not constitute more than 10 percent of the aggregate wall and ceiling area of any room or space.
    4. The flame spread index does not exceed 75 when tested in accordance with ASTM E84 or UL 723. The smoke-developed index is not limited.

    R303.5.10 Interior finish. Foam plastics used as interior finishes shall comply with Section R303.6 and shall meet the flame spread index and smoke-developed index requirements of Sections R302.9.1 and R302.9.2.

    R303.5.11 Sill plates and headers. Foam plastic spray applied to sill plates and headers or installed in the perimeter joist space without the thermal barrier specified in Section R303.4 shall comply with all of the following:

    1. The thickness of the foam plastic shall be not more than 3 [1] / 4 inches (83 mm).
    2. The density of the foam plastic shall be in the range of 0.5 to 2.0 pounds per cubic foot (8 to 32 kg/m [3] ).
    3. The foam plastic shall have a flame spread index of 25 or less and an accompanying smoke-developed index of 450 or less when tested in accordance with ASTM E84 or UL 723.
  • CBC § 903.3.1.1 High relevance — show source text

    Fixed or movable walls and partitions, paneling, wall pads and crash pads applied structurally or for decoration, acoustical correction, surface insulation or other purposes shall be considered to be interior finish, shall comply with Section 803 and shall not be considered to be decorative materials or furnishings.

    Exceptions:

    1. In auditoriums in Group A, the permissible amount of curtains, draperies, fabric hangings and similar combustible decorative materials suspended from walls or ceilings shall not exceed 75 percent of the aggregate wall area where the building is equipped throughout with an approved automatic sprinkler system in accordance with Section 903.3.1.1, and where the material is installed in accordance with Section 803.15 of this code.

    2. In Group R-2 dormitories, within sleeping units and dwelling units, the permissible amount of curtains, draperies, fabric hangings and similar decorative materials suspended from walls or ceiling shall not exceed 50 percent of the aggregate wall areas where the building is equipped throughout with an approved automatic sprinkler system installed in accordance with Section 903.3.1.

    3. In Group B and M occupancies, the amount of combustible fabric partitions suspended from the ceiling and not supported by the floor shall comply with Section 806.4 and shall not be limited.

    4. The 10-percent limit shall not apply to curtains, draperies, fabric hangings and similar combustible decorative materials used as window coverings.

    [F] 806.3 Occupancy-based requirements. Occupancy-based requirements for combustible decorative materials, other than decorative vegetation, not complying with Section 806.4 shall comply with Sections 807.5.1 through 807.5.6 of the California Fire Code .

    [F] 806.4 Acceptance criteria and reports. Where required to exhibit improved fire performance, curtains, draperies, fabric hangings and similar combustible decorative materials suspended from walls or ceilings shall be tested by an approved agency and shall be flame resistant in accordance with the provisions set forth in CCR, Title 19, Division 1, Chapter 8 . Reports of test results shall be prepared in accordance with the test method used and furnished to the building official on request.

    2025 CALIFORNIA BUILDING CODE 8-7

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

    INTERIOR FINISHES

    [F] 806.5 Pyroxylin plastic. Imitation leather or other material consisting of or coated with a pyroxylin or similarly hazardous base shall not be used in Group A occupancies.

    [F] 806.6 Interior trim. Material, other than foam plastic used as interior trim, shall have a minimum Class B flame spread and 450 smoke-developed index in Group I-3 and for all other occupancies Class C flame spread and smoke-developed index when tested in accordance with ASTM E84 or UL 723, as described in Section 803.1.2. Combustible trim, excluding handrails and guardrails, shall not exceed 10 percent of the specific wall or ceiling area to which it is attached.

    [F] 806.6.1 Foam plastic. Foam plastic used as interior trim in any occupancy shall comply with Section 2604.2.

  • CBC § 803.13 High relevance — show source text

    803.13 Laminated products factory produced with an attached wood substrate. Laminated products factory produced with an attached wood substrate shall comply with one of the following:

    1. The laminated product shall meet the criteria of Section 803.1.1 when tested in accordance with NFPA 286 using the product mounting system, including adhesive, of actual use.
    2. The laminated product shall have a Class A, B or C flame spread index and smoke-developed index based on the requirements of Table 803.3, in accordance with ASTM E84 or UL 723. Test specimen preparation and mounting shall be in accordance with ASTM E2579.

    8-6 2025 CALIFORNIA FIRE CODE

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    INTERIOR FINISH, DECORATIVE MATERIALS AND FURNISHINGS

    803.14 Thickness exemption. Materials having a thickness less than 0.036 inch (0.9 mm) applied directly to the surface of walls or ceilings shall not be required to be tested.

    803.15 Heavy timber exemption. Exposed portions of building elements complying with the requirements of Type IV construction in accordance with the California Building Code shall not be subject to interior finish requirements.

    SECTION 804—INTERIOR WALL AND CEILING TRIM AND INTERIOR FLOOR FINISH IN NEW AND EXISTING BUILDINGS

    804.1 Interior trim. Combustible trim in new and existing buildings, excluding handrails and guards, shall not exceed 10 percent of the specific wall or ceiling areas to which it is attached. Other than foam plastic, material used as interior trim shall have minimum Class B flame spread and 450 smoke-developed index in Group I-3 and for all other occupancies shall comply with Section 804.1.1 or 804.1.2. Foam plastic used as interior trim shall comply with Section 804.2.

    804.1.1 Testing in accordance with NFPA 286. Interior trim material shall be tested in accordance with NFPA 286 and comply with the acceptance criteria in Section 803.1.1.1. Where the interior trim material has been tested as an interior finish in accordance with NFPA 286 and complies with the acceptance criteria in Section 803.1.1.1, it shall not be required to be tested for flame spread index and smoke-developed index in accordance with ASTM E84 or UL 723.

    804.1.2 Testing in accordance with ASTM E84 or UL 723. Material, other than foam plastic, used as interior trim shall have minimum Class C flame spread and smoke-developed indices, when tested in accordance with ASTM E84 or UL 723, as described in Section 803.1.2.

    804.2 Foam plastic interior trim. Foam plastic used as interior trim shall comply with Sections 804.2.1 through 804.2.4. 804.2.1 Density. The minimum density of the interior trim shall be 20 pounds per cubic foot (320 kg/m [3] ). 804.2.2 Thickness. The maximum thickness of the interior trim shall be [1] / 2 inch (12.7 mm) and the maximum width shall be 8 inches (203 mm).

    804.2.3 Area limitation. The interior trim shall not constitute more than 10 percent of the specific wall or ceiling area to which it is attached.

  • CBC § 26-6 High relevance — show source text

    Exceptions:

    1. Buildings where the structural members of walls, floors, ceilings and roofs are entirely of noncombustible materials or preservative-treated wood.

    26-6 2025 CALIFORNIA BUILDING CODE

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    PLASTIC

    1. An approved method of protecting the foam plastic and structure from subterranean termite damage is provided.

    2. On the interior side of basement walls.

    FIGURE 2603.8—TERMITE INFESTATION PROBABILITY MAP

    2603.9 Special approval. Foam plastic shall not be required to comply with the requirements of Section 2603.4 or those of Section 2603.6 where specifically approved based on one of the following large-scale tests:

    1. NFPA 286 using the acceptance criteria of Section 803.1.1.1.

    2. FM 4880.

    3. UL 1040.

    4. UL 1715.

    Such testing shall be performed on the finished manufactured foam plastic assembly in the maximum thickness intended for use. Foam plastics that are used as interior finish on the basis of these tests shall also conform to the flame spread and smoke-developed requirements of Chapter 8. Assemblies tested shall include seams, joints and other typical details used in the installation of the assembly and shall be tested in the manner intended for use.

    [BS] 2603.10 Wind resistance. Foam plastic insulation complying with ASTM C578 and ASTM C1289 and used as exterior wall sheathing on framed wall assemblies shall comply with ANSI/SBCA FS 100 for wind pressure resistance.

    SECTION 2604—INTERIOR FINISH AND TRIM

    2604.1 General. Plastic materials installed as interior finish or trim shall comply with Chapter 8. Foam plastics shall only be installed as interior finish where approved in accordance with the special provisions of Section 2603.9. Foam plastics that are used as interior finish shall meet the flame spread and smoke-developed index requirements for interior finish in accordance with Chapter 8. Foam plastics installed as interior trim shall comply with Section 2604.2. 2604.1.1 Plenums. Foam plastics installed in plenums as interior wall or ceiling finish shall comply with Section 2603.7. Foam plastics installed in plenums as interior trim shall comply with Sections 2604.2 and 2603.7.

    [F] 2604.2 Interior trim. Foam plastic used as interior trim shall comply with Sections 2604.2.1 through 2604.2.4.

    [F] 2604.2.1 Density. The minimum density of the interior trim shall be 20 pcf (320 kg/m [3] ).

    [F] 2604.2.2 Thickness. The maximum thickness of the interior trim shall be [1] / 2 inch (12.7 mm) and the maximum width shall be 8 inches (204 mm).

    [F] 2604.2.3 Area limitation. The interior trim shall not constitute more than 10 percent of the specific wall or ceiling areas to which it is attached.

    [F] 2604.2.4 Flame spread. The flame spread index shall not exceed 75 where tested in accordance with ASTM E84 or UL 723. The smoke-developed index shall not be limited.

  • CBC § 2603.5.7 High relevance — show source text

    2603.5.7 Ignition. Exterior walls shall not exhibit sustained flaming where tested in accordance with NFPA 268. Where a material is intended to be installed in more than one thickness, tests of the minimum and maximum thickness intended for use shall be performed.

    Exception: Assemblies protected on the outside with one of the following:

    1. A thermal barrier complying with Section 2603.4.
    2. A minimum 1-inch (25 mm) thickness of concrete or masonry.
    3. Glass-fiber-reinforced concrete panels of a minimum thickness of [3] / 8 inch (9.5 mm).
    4. Metal-faced panels having minimum 0.019-inch-thick (0.48 mm) aluminum or 0.016-inch-thick (0.41 mm) corrosionresistant steel outer facings.
    5. A minimum [7] / 8 -inch (22.2 mm) thickness of stucco complying with Section 2510.
    6. A minimum [1] / 4 -inch (6.4 mm) thickness of fiber-cement lap, panel or shingle siding complying with Section 1404.17 and Section 1404.17.1 or 1404.17.2.

    2603.6 Roofing. Foam plastic insulation meeting the requirements of Sections 2603.2, 2603.3 and 2603.4 shall be permitted as part of a roof-covering assembly, provided that the assembly with the foam plastic insulation is a Class A, B or C roofing assembly where tested in accordance with ASTM E108 or UL 790.

    2603.7 Foam plastic in plenums as interior finish or interior trim. Foam plastic in plenums used as interior wall or ceiling finish, or interior trim, shall exhibit a flame spread index of 25 or less and a smoke-developed index of 50 or less when tested in accordance with ASTM E84 or UL 723 at the maximum thickness and density intended for use, and shall be tested in accordance with NFPA 286 and meet the acceptance criteria of Section 803.1.1. As an alternative to testing to NFPA 286, the foam plastic shall be approved based on tests conducted in accordance with Section 2603.9.

    Exceptions:

    1. Foam plastic in plenums used as interior wall or ceiling finish, or interior trim, shall exhibit a flame spread index of 75 or less and a smoke-developed index of 450 or less when tested in accordance with ASTM E84 or UL 723 at the maximum thickness and density intended for use, where it is separated from the airflow in the plenum by a thermal barrier complying with Section 2603.4.
    2. Foam plastic in plenums used as interior wall or ceiling finish, or interior trim, shall exhibit a flame spread index of 75 or less and a smoke-developed index of 450 or less when tested in accordance with ASTM E84 or UL 723 at the maximum thickness and density intended for use, where it is separated from the airflow in the plenum by corrosion-resistant steel having a base metal thickness of not less than 0.0160 inch (0.4 mm).
    3. Foam plastic in plenums used as interior wall or ceiling finish, or interior trim, shall exhibit a flame spread index of 75 or less and a smoke-developed index of 450 or less when tested in accordance with ASTM E84 or UL 723 at the maximum thickness and density intended for use, where it is separated from the airflow in the plenum by not less than a 1-inch (25 mm) thickness of masonry or concrete.
  • CBC § 3-27 High relevance — show source text

    2025 CALIFORNIA RESIDENTIAL CODE 3-27

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

    BUILDING PLANNING

    TABLE R302.6—DWELLING UNIT GARAGE AND/OR CARPORT SEPARATION Col2
    ** SEPARATION** ** MATERIAL**
    From the dwelling unit and attics Not less than1/2-inch gypsum board or equivalent applied to the garage side
    From portions of the dwelling unit above the garage_or carport_ Not less than5/8-inch Type X gypsum board or equivalent
    Structure supporting floor/ceiling assemblies used for separation
    required by this section    		 Not less than1/2-inch gypsum board or equivalent
    Garages located less than 3 feet from a dwelling unit on the same lot Not less than1/2-inch gypsum board or equivalent applied to the interior
    side of exterior walls that are within this area
    For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm. For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.

    R302.7 Under-stair protection. Enclosed space under stairs that is accessed by a door or access panel shall have walls, under-stair surface and any soffits protected on the enclosed side with [1] / 2 -inch (12.7 mm) gypsum board.

    R302.8 Foam plastics. For requirements for foam plastics, see Section R303.

    R302.8.1 Interior finish. Foam plastics used as interior finishes shall comply with Section R303.5.10.

    R302.9 Flame spread index and smoke-developed index for wall and ceiling finishes. Flame spread and smoke-developed indices for wall and ceiling finishes shall be in accordance with Sections R302.9.1 through R302.9.4.

    R302.9.1 Flame spread index. Wall and ceiling finishes shall have a flame spread index of not greater than 200.

    Exception: Flame spread index requirements for finishes shall not apply to trim defined as picture molds, chair rails, baseboards and handrails; to doors and windows or their frames; or to materials that are less than [1] / 28 inch (0.91 mm) in thickness cemented to the surface of walls or ceilings if these materials exhibit flame spread index values not greater than those of paper of this thickness cemented to a noncombustible backing.

    R302.9.2 Smoke-developed index. Wall and ceiling finishes shall have a smoke-developed index of not greater than 450.

    R302.9.3 Testing. Tests shall be made in accordance with ASTM E84 or UL 723.

    R302.9.4 Alternative test method. As an alternative to having a flame spread index of not greater than 200 and a smoke-developed index of not greater than 450 where tested in accordance with ASTM E84 or UL 723, wall and ceiling finishes shall be permitted to be tested in accordance with NFPA 286. Materials tested in accordance with NFPA 286 shall meet the following criteria:

    The interior finish shall comply with the following:

    1. During the 40 kW exposure, flames shall not spread to the ceiling.
    2. The flame shall not spread to the outer extremity of the sample on any wall or ceiling.
    3. Flashover, as defined in NFPA 286, shall not occur.
  • CBC § 5.5 High relevance — show source text

    [BSC-CG] See California Green Building Standards Code, Chapter 5, Division 5.5 for additional finish material pollutant control requirements.

    SECTION 802—GENERAL

    802.1 Interior wall and ceiling finish. The provisions of Section 803 shall limit the allowable fire performance and smoke development of interior wall and ceiling finish materials based on occupancy classification.

    802.2 Interior floor finish. The provisions of Section 804 shall limit the allowable fire performance of interior floor finish materials based on occupancy classification.

    [F] 802.3 Decorative materials and trim. Decorative materials and trim shall be restricted by combustibility, fire performance or flame propagation performance criteria in accordance with Section 806.

    802.4 Applicability. For buildings in flood hazard areas as established in Section 1612.3, interior finishes, trim and decorative materials below the elevation required by Section 1612 shall be flood-damage-resistant materials.

    802.5 Application. Combustible materials shall be permitted to be used as finish for walls, ceilings, floors and other interior surfaces of buildings.

    802.6 Windows. Show windows in the exterior walls of the first story above grade plane shall be permitted to be of wood or of unprotected metal framing.

    802.7 Foam plastics. Foam plastics shall not be used as interior finish except as provided in Section 803.4. Foam plastics shall not be used as interior trim except as provided in Section 806.6.1 or 2604.2. This section shall apply both to exposed foam plastics and to foam plastics used in conjunction with a textile or vinyl facing or cover.

    SECTION 803—WALL AND CEILING FINISHES

    803.1 General. Interior wall and ceiling finish materials shall be classified for fire performance and smoke development in accordance with Section 803.1.1 or 803.1.2, except as shown in Sections 803.1.3 through 803.15. Materials tested in accordance with Section 803.1.1 shall not be required to be tested in accordance with Section 803.1.2.

    803.1.1 Interior wall and ceiling finish materials tested in accordance with NFPA 286. Interior wall and ceiling finish materials shall be classified in accordance with NFPA 286 and comply with Section 803.1.1.1. Materials complying with Section 803.1.1.1 shall be considered to also comply with the requirements of Class A.

    803.1.1.1 Acceptance criteria for NFPA 286. The interior finish shall comply with the following:

    1. During the 40 kW exposure, flames shall not spread to the ceiling.

    2. The flame shall not spread to the outer extremity of the sample on any wall or ceiling.

    3. Flashover, as defined in NFPA 286, shall not occur.

    4. The peak heat release rate throughout the test shall not exceed 800 kW.

    5. The total smoke released throughout the test shall not exceed 1,000 m [2] .

    803.1.2 Interior wall and ceiling finish materials tested in accordance with ASTM E84 or UL 723. Interior wall and ceiling finish materials shall be classified in accordance with ASTM E84 or UL 723. Such interior finish materials shall be grouped in the following classes in accordance with their flame spread and smoke-developed indices.

    Class A = Flame spread index 0–25; smoke-developed index 0–450.

    Class B = Flame spread index 26–75; smoke developed index 0–450.

    Class C = Flame spread index 76–200; smoke-developed index 0–450.

  • CBC § 2603.4. High relevance — show source text

    Exceptions:

    1. Foam plastic in plenums used as interior wall or ceiling finish, or interior trim, shall exhibit a flame spread index of 75 or less and a smoke-developed index of 450 or less when tested in accordance with ASTM E84 or UL 723 at the maximum thickness and density intended for use, where it is separated from the airflow in the plenum by a thermal barrier complying with Section 2603.4.
    2. Foam plastic in plenums used as interior wall or ceiling finish, or interior trim, shall exhibit a flame spread index of 75 or less and a smoke-developed index of 450 or less when tested in accordance with ASTM E84 or UL 723 at the maximum thickness and density intended for use, where it is separated from the airflow in the plenum by corrosion-resistant steel having a base metal thickness of not less than 0.0160 inch (0.4 mm).
    3. Foam plastic in plenums used as interior wall or ceiling finish, or interior trim, shall exhibit a flame spread index of 75 or less and a smoke-developed index of 450 or less when tested in accordance with ASTM E84 or UL 723 at the maximum thickness and density intended for use, where it is separated from the airflow in the plenum by not less than a 1-inch (25 mm) thickness of masonry or concrete.

    2603.8 Protection against termites. In areas where the probability of termite infestation is very heavy in accordance with Figure 2603.8, extruded and expanded polystyrene, polyisocyanurate and other foam plastics shall not be installed on the exterior face or under interior or exterior foundation walls or slab foundations located below grade. The clearance between foam plastics installed above grade and exposed earth shall be not less than 6 inches (152 mm).

    Exceptions:

    1. Buildings where the structural members of walls, floors, ceilings and roofs are entirely of noncombustible materials or preservative-treated wood.

    26-6 2025 CALIFORNIA BUILDING CODE

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

    PLASTIC

    1. An approved method of protecting the foam plastic and structure from subterranean termite damage is provided.

    2. On the interior side of basement walls.

    FIGURE 2603.8—TERMITE INFESTATION PROBABILITY MAP

    2603.9 Special approval. Foam plastic shall not be required to comply with the requirements of Section 2603.4 or those of Section 2603.6 where specifically approved based on one of the following large-scale tests:

    1. NFPA 286 using the acceptance criteria of Section 803.1.1.1.

    2. FM 4880.

    3. UL 1040.

    4. UL 1715.

    Such testing shall be performed on the finished manufactured foam plastic assembly in the maximum thickness intended for use. Foam plastics that are used as interior finish on the basis of these tests shall also conform to the flame spread and smoke-developed requirements of Chapter 8. Assemblies tested shall include seams, joints and other typical details used in the installation of the assembly and shall be tested in the manner intended for use.

    [BS] 2603.10 Wind resistance. Foam plastic insulation complying with ASTM C578 and ASTM C1289 and used as exterior wall sheathing on framed wall assemblies shall comply with ANSI/SBCA FS 100 for wind pressure resistance.

    SECTION 2604—INTERIOR FINISH AND TRIM

  • CBC § 803.13 High relevance — show source text

    1||X||||||||||||||||||||||| |Table 803.13|||X|||||||||||||||||||||| |804.1|||X|||||||||||||||||||||| |804.4|||X|||||||||||||||||||||| |804.4.1|||X|||||||||||||||||||||| |804.4.2|||X|||||||||||||||||||||| |804.4.3|||X|||||||||||||||||||||| |806.4|||X|||||||||||||||||||||| |806.6|||X||||||||||||||||||||||

    The state agency does not adopt sections identified by the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.

    2025 CALIFORNIA BUILDING CODE 8-1

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

    8-2 2025 CALIFORNIA BUILDING CODE

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

    8 INTERIOR FINISHES

    User notes:

    About this chapter: Chapter 8 contains the performance requirements for controlling fire growth and smoke propagation within buildings by restricting interior finish and decorative materials. The provisions of this chapter require materials used as interior finishes and decorations to meet certain flame spread index or flame propagation criteria and smoke development criteria based on the relative fire hazard associated with the occupancy. The performance of the material is evaluated based on test standards.

    SECTION 801—SCOPE

    801.1 Scope. The provisions of this chapter shall govern the use of materials used as interior finishes, trim and decorative materials.

    [BSC-CG] See California Green Building Standards Code, Chapter 5, Division 5.5 for additional finish material pollutant control requirements.

    SECTION 802—GENERAL

    802.1 Interior wall and ceiling finish. The provisions of Section 803 shall limit the allowable fire performance and smoke development of interior wall and ceiling finish materials based on occupancy classification.

    802.2 Interior floor finish. The provisions of Section 804 shall limit the allowable fire performance of interior floor finish materials based on occupancy classification.

    [F] 802.3 Decorative materials and trim. Decorative materials and trim shall be restricted by combustibility, fire performance or flame propagation performance criteria in accordance with Section 806.

    802.4 Applicability. For buildings in flood hazard areas as established in Section 1612.3, interior finishes, trim and decorative materials below the elevation required by Section 1612 shall be flood-damage-resistant materials.

    802.5 Application. Combustible materials shall be permitted to be used as finish for walls, ceilings, floors and other interior surfaces of buildings.

    802.6 Windows. Show windows in the exterior walls of the first story above grade plane shall be permitted to be of wood or of unprotected metal framing.

    802.7 Foam plastics. Foam plastics shall not be used as interior finish except as provided in Section 803.4. Foam plastics shall not be used as interior trim except as provided in Section 806.6.1 or 2604.2. This section shall apply both to exposed foam plastics and to foam plastics used in conjunction with a textile or vinyl facing or cover.

    SECTION 803—WALL AND CEILING FINISHES

Frequently asked questions

Can I use foam crown molding anywhere if it’s less than 1/2" thick?

Not automatically. Foam interior trim must also meet minimum density (20 pcf), width limit (≤ 8 in), the 10% area limitation, and flame‑spread index ≤ 75 when tested to ASTM E84/UL 723 unless NFPA 286 testing is used for acceptance (§2604.2) .

How do I calculate the 10% trim area limit in a multi‑wall room?

Apply the 10% limit to the specific wall(s) or ceiling area where the trim is attached. The code language is “specific wall or ceiling areas to which it is attached,” so check each wall or ceiling segment separately rather than summing unrelated surfaces §806.6 and §2604.2.3 .

What if my trim meets NFPA 286 testing?

If the trim material or assembly has been tested as interior finish under NFPA 286 and meets the acceptance criteria in §803.1.1.1, you need not provide ASTM E84/UL 723 flame‑spread data for that trim; NFPA 286 acceptance can be used instead (§2604.2 exception and §803.1.1.1) .

Do handrails count toward the 10% limit?

No. Handrails and guardrails are excluded from the 10% combustible‑trim area limitation in §806.6 .

Are smoke‑developed index values limited for foam trim?

§2604.2 sets a flame‑spread ceiling (≤ 75) for foam trim tested by ASTM E84/UL 723 and states the smoke‑developed index is not limited by that section; other sections (e.g., plenum rules or occupancy requirements) may impose smoke limits in special circumstances §2604.2.4 .

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