CBC · California Building Code

When may foam plastics be used as interior finish or trim and what tests are required?

Foam plastic panels or moldings can be used inside buildings only when they meet specific California Building Code tests and limits: exposed foam finish generally requires large‑scale approval (NFPA 286 or the other tests listed in § 2603.9) tested on the finished assembly; foam trim can be used if it meets the density, thickness, width, area and flame‑spread limits in § 2604.2; and foam in plenums must meet much stricter indices or be separated by an approved thermal barrier.

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Last reviewed: July 5, 2026

What the code requires — 2–4 sentences

Foam plastics are generally prohibited as interior wall or ceiling finish unless they are specifically approved by the large‑scale test methods listed in § 2603.9; this is the controlling approval route for exposed foam finish materials (see § 803.4 and § 2603.9). Foam plastics may be used as interior trim only if they meet the dimensional, density and flame‑spread limits in § 2604.2 (or if the trim has been tested as an interior finish per NFPA 286 and meets the acceptance criteria in § 803.1.1.1). Plenum installations have the most restrictive limits and special testing requirements in § 2603.7.

Requirements in detail

High‑level decision tree (where you must look first)

  • Is the foam plastic intended as interior wall/ceiling finish (exposed as finish)? — See § 803.4 and § 2603.9.
  • Is it interior trim (molding, rosettes, cornice, etc.)? — See § 2604.2.
  • Is it inside a plenum (air plenum or return plenum)? — See § 2603.7 (much stricter limits).

Key numeric and test requirements (decision‑relevant dimensions)

Use case Required test / performance rule Decision‑relevant value(s) Code Reference
Interior wall or ceiling finish (exposed foam) Large‑scale acceptance testing (NFPA 286 using § 803.1.1.1 criteria, or FM 4880, UL 1040, UL 1715); test finished assembly at maximum thickness and include seams/joints. Also must conform to Chapter 8 flame/smoke requirements. Test on finished manufactured assembly at maximum thickness intended for use; acceptance per NFPA 286 criteria (including § 803.1.1.1 heat/smoke limits). § 803.4; § 2603.9; § 803.1.1.1
Interior trim (exposed foam trim) ASTM E84 / UL 723 flame‑spread testing (unless NFPA 286 finish testing used as exception). Also density, thickness, width and area limits. Minimum density 20 pcf (320 kg/m3); max thickness 1/2 in (12.7 mm); max width 8 in (204 mm); trim ≤10% of the wall/ceiling area where attached; flame spread index ≤75 (ASTM E84 / UL 723); smoke‑developed not limited. § 2604.2.1–2604.2.4
Plenums — foam as finish or trim Very restrictive: ASTM E84 / UL 723 flame spread index 25 or less and smoke‑developed 50 or less at maximum thickness/density AND tested in accordance with NFPA 286 meeting § 803.1.1 acceptance; alternative approval may be via § 2603.9 tests. Exceptions allow higher indices if separated from plenum airflow by approved thermal barrier, steel facing or masonry. Flame spread ≤25 and smoke ≤50 (standard requirement in plenums); exceptions: up to flame spread 75 / smoke 450 if separated from airflow by thermal barrier (§ 2603.4), by corrosion‑resistant steel ≥0.0160 in, or by ≥1 in masonry/concrete. § 2603.7 (and exceptions)

Notes on testing scope and assembly preparation:

  • Where a foam plastic is approved by large‑scale testing under § 2603.9, the tests must be performed on the finished manufactured foam plastic assembly at the maximum thickness intended for use and shall include seams, joints and other typical installation details and be tested in the manner intended for use. Foam plastics used as interior finish on the basis of these tests must also conform to Chapter 8 flame spread and smoke‑developed requirements.

Required test methods and acceptance references

  • NFPA 286 using the acceptance criteria in § 803.1.1.1 (this large‑scale room corner test is the primary acceptance route cited in § 2603.9).
  • FM 4880, UL 1040, or UL 1715 are alternate large‑scale tests listed in § 2603.9 for special approval of foam plastics used as interior finish. Tests must be on the finished assembly at maximum thickness.
  • ASTM E84 / UL 723 (tunnel test) is used for flame‑spread classification for trim and for many finish classifications in Chapter 8; plenums require more restrictive indices (see § 2603.7).

Exceptions & special cases

  • Trim tested as interior finish by NFPA 286: If interior trim is tested as an interior finish in accordance with NFPA 286 and meets the acceptance criteria in § 803.1.1.1, the trim is not required to be tested for flame spread by ASTM E84 / UL 723 (effectively the NFPA 286 result allows the ASTM E84 requirement to be waived for that trim).
  • Plenum exceptions (higher allowable E84 indices) apply only if the foam is separated from plenum airflow by an approved thermal barrier (per § 2603.4), or by corrosion‑resistant steel ≥0.0160 in base metal thickness, or by ≥1 in of masonry/concrete. These exceptions are stated explicitly in § 2603.7.
  • Thermal barrier routes: foam plastic may also be used where separated from interior by an approved thermal barrier in accordance with § 2603.4 (see the thermal barrier provisions for permitted alternative protection strategies). If no special test approval under § 2603.9 is obtained, a thermal barrier is a common compliance path.

If a code text or topic you expect is missing from the files I retrieved, I will say so plainly: the supplied files contain the controlling text for § 803.4, § 2603.9, § 2603.7 and § 2604.2 (and related Chapter 8 provisions), and those are the bases for the statements above. I did not find any additional California‑specific alternative test acceptance criteria beyond the ones listed in § 2603.9 in the provided files.

Common mistakes

  • Treating ASTM E84 (tunnel test) as sufficient for exposed foam used as interior finish — in California exposed foam finish generally requires the large‑scale approvals in § 2603.9 (for finish) or an approved thermal barrier per § 2603.4; don’t assume a Class B or C E84 result is enough for “finish.”
  • Forgetting trim dimensional and density limits — interior foam trim must be ≥20 pcf and ≤1/2" thick and ≤8" wide and must not exceed 10% of the wall/ceiling area unless you rely on NFPA 286 finish testing. Verify density on product data and test at maximum thickness.
  • Testing samples at non‑representative thickness or omitting seams/joints — § 2603.9 explicitly requires testing the finished assembly at the maximum thickness intended and including typical installation details.
  • Installing foam in plenums without meeting the much stricter plenum indices or without an approved separation (thermal barrier, steel facing or masonry). Plenum criteria are significantly stricter than general room finish or trim limits.

Worked example

Scenario: A designer wants to install factory‑made decorative wall panels of extruded polystyrene (XPS) used as exposed wall finish. Panels are 3/4 inch thick, include taped seams, and the manufacturer proposes approval based on NFPA 286 testing of the finished panel assembly.

What the code requires and how to check compliance:

  1. Because the product is exposed foam serving as interior wall finish, § 803.4 directs that exposed foam finish is only allowed per § 2603.9—so large‑scale approval is required (ASTM E84 alone will not suffice). You must use one of the listed large‑scale tests: NFPA 286 (using § 803.1.1.1 acceptance), FM 4880, UL 1040 or UL 1715. The NFPA 286 test must be performed on the finished assembly at the maximum thickness intended for use and include seams/joints and mounting as intended.
  2. If the NFPA 286 test report for the finished 3/4" assembly shows compliance with the NFPA 286 acceptance criteria in § 803.1.1.1 (no ceiling spread, no spread to outer extremity, no flashover, peak HRR ≤800 kW, total smoke ≤1,000 m2), then the product can be accepted as interior finish under § 2603.9/§ 803.1.1.1, provided the test sample exactly represents the installed assembly (seams, adhesives, thickness).
  3. The test must be on the finished manufactured assembly at the maximum thickness intended for use; if the manufacturer only tested 1/2" thickness but plans to sell 3/4", the test is not sufficient. § 2603.9 requires maximum thickness testing.

If instead the panels were intended as decorative trim (≤1/2" thick, 4" wide, used as picture rails covering 6% of a wall), you would: confirm density ≥20 pcf, thickness ≤1/2" and width ≤8", area ≤10% and confirm ASTM E84 flame‑spread ≤75 (or have the trim tested as interior finish by NFPA 286 and meet § 803.1.1.1, which would negate the need for an E84 test for flame spread).

Related provisions (use these sections for deeper cross‑checks)

  • § 803.1.1.1 — NFPA 286 acceptance criteria for interior finish (heat release and smoke acceptance limits).
  • § 803.4 — Foam plastics shall not be used as interior finish except as provided in § 2603.9.
  • § 2603.9 — Special approval: lists NFPA 286 (with § 803.1.1.1 acceptance) and FM 4880, UL 1040, UL 1715 as allowable test routes and requires testing at maximum thickness and finished assembly.
  • § 2603.7 — Plenum requirements and exceptions (very restrictive flame/smoke indices or separation/thermal barrier options).
  • § 2603.4 — Thermal barrier provisions that can affect where foam plastics are permitted without large‑scale finish testing.
  • § 2604.2 — Specific interior trim numeric limits: density, thickness, width, area, and flame‑spread limit.

Code references

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

  • 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

    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

    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 § 2603.4. 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 § 803.9 High relevance — show source text

    [BF] 803.9 High-density polyethylene (HDPE) and polypropylene (PP). Where high-density polyethylene or polypropylene is used as an interior finish, it shall comply with Section 803.1.1.

    [BF] 803.10 Site-fabricated stretch systems. Where used as newly installed interior wall or interior ceiling finish materials, sitefabricated stretch systems containing all three components described in the definition in Chapter 2 shall be tested in the manner intended for use, and shall comply with the requirements of Section 803.1.1 or 803.1.2. If the materials are tested in accordance with ASTM E84 or UL 723, specimen preparation and mounting shall be in accordance with ASTM E2573.

    803.11 Foam plastic materials. Foam plastic materials shall not be used as interior wall and ceiling finish unless specifically allowed by Section 803.11.1 or 803.11.2. Foam plastic materials shall not be used as interior trim unless specifically allowed by Section 804.2.

    803.11.1 Foam plastics. Foam plastics shall be allowed to be used as interior wall and ceiling finish only where in accordance with Section 2603.9 of the California Building Code . This section shall apply both to exposed foam plastics and to foam plastics used in conjunction with a textile or vinyl facing or cover.

    803.11.2 Thermal barrier for foam plastics. Foam plastic material shall be allowed if it is separated from the interior of the building by a thermal barrier in accordance with Section 2603.4 of the California Building Code.

    803.12 Facings or wood veneers intended to be applied on site over a wood substrate. Facings or veneers intended to be applied on site over a wood substrate shall comply with one of the following:

    1. The facing or veneer shall meet the criteria of Section 803.1.1 when tested in accordance with NFPA 286 using the product mounting system, including adhesive, described in Section 5.8.9 of NFPA 286.
    2. The facing or veneer 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 E2404.

    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

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

    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.

  • 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 § 5.6 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

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

    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 § 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

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

    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 § 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 § 803.1.3 High relevance — show source text

    803.1.3 Interior wall and ceiling finish materials with different requirements. The materials indicated in Sections 803.2 through 803.13 shall be tested as indicated in the corresponding sections.

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    INTERIOR FINISHES

    803.2 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.

    803.3 Heavy timber exemption. Exposed portions of building elements complying with the requirements for buildings of heavy timber construction in Section 602.4 or Section 2304.11 shall not be subject to interior finish requirements except in interior exit stairways, interior exit ramps, and exit passageways.

    803.4 Foam plastics. Foam plastics shall not be used as interior finish except as provided in Section 2603.9. This section shall apply both to exposed foam plastics and to foam plastics used in conjunction with a textile or vinyl facing or cover.

    803.5 Textile wall coverings. Where used as interior wall finish materials, textile wall coverings, including materials having woven or nonwoven, napped, tufted, looped or similar surface and carpet and similar textile materials, shall be tested in the manner intended for use, using the product-mounting system, including adhesive, and shall comply with the requirements of one of the following: Section 803.1.1, 803.5.1 or 803.5.2.

    803.5.1 Room corner test for textile wall coverings and expanded vinyl wall coverings. Textile wall coverings and expanded vinyl wall coverings shall meet the criteria of Section 803.5.1.1 when tested in the manner intended for use in accordance with the Method B protocol of NFPA 265 using the product-mounting system, including adhesive.

    803.5.1.1 Acceptance criteria for NFPA 265. 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 extremities of the samples on the 8-foot by 12-foot (203 by 305 mm) walls.
    3. Flashover, as defined in NFPA 265, shall not occur.
    4. The total smoke release throughout the test shall not exceed 1,000 m [2] .

    803.5.2 Acceptance criteria for textile and expanded vinyl wall or ceiling coverings tested to ASTM E84 or UL 723. Textile wall and ceiling coverings and expanded vinyl wall and ceiling coverings shall have a Class A flame spread index in accordance with ASTM E84 or UL 723 and be protected by an automatic sprinkler system installed in accordance with Section 903.3.1.1 or 903.3.1.2. Test specimen preparation and mounting shall be in accordance with ASTM E2404.

    803.6 Textile ceiling coverings. Where used as interior ceiling finish materials, textile ceiling coverings, including materials having woven or nonwoven, napped, tufted, looped or similar surface and carpet and similar textile materials, shall be tested in the manner intended for use, using the product-mounting system, including adhesive, and shall comply with the requirements of Section 803.1.1 or 803.5.2.

  • 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.

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    8-2 2025 CALIFORNIA BUILDING CODE

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    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

  • CBC § 803.5.2 High relevance — show source text

    803.5.2 Acceptance criteria for wall and ceiling coverings. Textile wall and ceiling coverings shall have a Class A flame spread index in accordance with ASTM E84 or UL 723, and be protected by an automatic sprinkler system installed in accordance with Section 903.3.1.1 or 903.3.1.2. Test specimen preparation and mounting shall be in accordance with ASTM E2404.

    803.6 Textile ceiling coverings. Where used as interior ceiling finish materials, textile ceiling coverings, including materials having a woven, nonwoven, napped, tufted, looped or similar surface and carpet or similar textile materials, shall be tested in the manner intended for use, using the product mounting system, including adhesive, and shall comply with the requirements of Section 803.1.1 or 803.5.2.

    803.7 Expanded vinyl wall coverings. Where used as interior wall finish materials, expanded vinyl wall coverings shall be tested in the manner intended for use, using the product mounting system, including adhesive, and shall comply with the requirements of Section 803.1.1, 803.5.1 or 803.5.2.

    803.8 Expanded vinyl ceiling coverings. Where used as interior ceiling finish materials, expanded vinyl ceiling coverings shall be tested in the manner intended for use, using the product mounting system, including adhesive, and shall comply with the requirements of Section 803.1.1 or 803.5.2.

    [BF] 803.9 High-density polyethylene (HDPE) and polypropylene (PP). Where high-density polyethylene or polypropylene is used as an interior finish, it shall comply with Section 803.1.1.

    [BF] 803.10 Site-fabricated stretch systems. Where used as newly installed interior wall or interior ceiling finish materials, sitefabricated stretch systems containing all three components described in the definition in Chapter 2 shall be tested in the manner intended for use, and shall comply with the requirements of Section 803.1.1 or 803.1.2. If the materials are tested in accordance with ASTM E84 or UL 723, specimen preparation and mounting shall be in accordance with ASTM E2573.

    803.11 Foam plastic materials. Foam plastic materials shall not be used as interior wall and ceiling finish unless specifically allowed by Section 803.11.1 or 803.11.2. Foam plastic materials shall not be used as interior trim unless specifically allowed by Section 804.2.

    803.11.1 Foam plastics. Foam plastics shall be allowed to be used as interior wall and ceiling finish only where in accordance with Section 2603.9 of the California Building Code . This section shall apply both to exposed foam plastics and to foam plastics used in conjunction with a textile or vinyl facing or cover.

    803.11.2 Thermal barrier for foam plastics. Foam plastic material shall be allowed if it is separated from the interior of the building by a thermal barrier in accordance with Section 2603.4 of the California Building Code.

  • CBC § 2603.4.1.10 High relevance — show source text

    2603.4.1.10 Siding backer board. Foam plastic insulation of not more than 2,000 British thermal units per square feet (Btu/sq. ft.) (22.7 mJ/m [2] ) as determined by NFPA 259 shall be permitted as a siding backer board with a maximum thickness of [1] / 2 inch (12.7 mm), provided that it is separated from the interior of the building by not less than 2 inches (51 mm) of mineral fiber insulation or equivalent or where applied as insulation with re-siding over existing wall construction.

    2603.4.1.11 Interior trim. Foam plastic used as interior trim in accordance with Section 2604 shall be permitted without a thermal barrier.

    2603.4.1.12 Interior signs. Foam plastic used for interior signs in covered mall buildings in accordance with Section 402.6.4 shall be permitted without a thermal barrier. Foam plastic signs that are not affixed to interior building surfaces shall comply with Chapter 8 of the California Fire Code.

    2603.4.1.13 Type V construction. Foam plastic spray applied to a sill plate, joist header and rim joist in Type V construction is subject to all of the following:

    1. The maximum thickness of the foam plastic shall be 3 [1] / 4 inches (82.6 mm).
    2. The density of the foam plastic shall be in the range of 1.5 to 2.0 pcf (24 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.

    2603.4.1.14 Floors. The thermal barrier specified in Section 2603.4 is not required to be installed on the walking surface of a structural floor system that contains foam plastic insulation where the foam plastic is covered by a minimum nominal [1] / 2 -inchthick (12.7 mm) wood structural panel or approved equivalent. The thermal barrier specified in Section 2603.4 is required on the underside of the structural floor system that contains foam plastic insulation where the underside of the structural floor system is exposed to the interior of the building.

    Exception: Foam plastic used as part of an interior floor finish.

    2603.4.1.15 Separately controlled climate structures. In nonsprinklered buildings of Group U, foam plastic having a thickness that does not exceed 4 inches (102 mm) and a maximum flame spread index of 75 is permitted in separately controlled climate structures where the aggregate floor area does not exceed 400 square feet (37 m [2] ) and the foam plastic is covered by a metal facing not less than 0.032-inch-thick (0.81 mm) aluminum or corrosion-resistant steel having a minimum base metal thickness of 0.016 inch (0.41mm). A thickness of up to 10 inches (254 mm) is permitted where protected by a thermal barrier.

Frequently asked questions

Can I use ordinary foam moulding (1/4" thick) as interior trim without testing?

Yes — very thin materials less than the thickness limits in Chapter 8 or those meeting the trim rules may be exempt from some tests; however for foam trim the specific § 2604.2 density/thickness/area and flame spread limits govern. Always confirm the product meets § 2604.2 requirements.

If a product passes ASTM E84 with flame spread 60, can it be used as exposed foam wall finish?

Not automatically. Exposed foam used as interior finish is controlled by § 803.4 and § 2603.9 and generally needs one of the large‑scale approvals (NFPA 286 per § 803.1.1.1, FM 4880, UL 1040, UL 1715) performed on the finished assembly at maximum thickness. ASTM E84 alone is typically not sufficient for exposed foam finish. cite

What is the simplest compliance path for foam used in a plenum?

The simplest path is to avoid exposed foam in plenums. If foam must be in a plenum, meet § 2603.7’s strict indices (flame spread ≤25 and smoke ≤50 tested at maximum thickness/density and NFPA 286) or use the specified separations (approved thermal barrier per § 2603.4, metal facing ≥0.0160 in, or ≥1 in masonry) that allow relaxed E84 limits.

If I have factory panels that are wrapped in fabric, does that change testing?

Yes—Chapter 8 and § 803.11 note that foam plastics used in conjunction with a textile or vinyl facing are still treated as foam plastics for the purposes of these provisions; testing must represent the finished facing and mounting as installed, and approval routes of § 2603.9 or thermal barrier approaches still apply.

Must smoke‑developed index be limited for foam trim?

For foam trim under § 2604.2 the flame‑spread index must not exceed 75 when tested to ASTM E84 or UL 723; the smoke‑developed index for that trim is not limited by § 2604.2. However other occupancy or Chapter 8 rules may impose additional controls.

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