CBC · California Building Code

What are flame‑spread/smoke limits for insulation and related materials?

Insulation in California buildings must generally test at flame‑spread ≤25 and smoke‑developed ≤450 (ASTM E84/UL723) for both concealed and exposed installations (Section 720), with specific exceptions for cellulosic loose‑fill and separate rules for foam plastics; Section 807 directs you to Section 720 for insulation compliance.

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Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

Thermal and acoustical insulation installed in California buildings must meet the surface‑burning (flame‑spread and smoke‑developed) limits specified in Section 720 of the CBC; Section 807 simply ties insulation to the requirements of Section 720. In plain terms: for both concealed and exposed insulation the code generally limits flame‑spread index to 25 and smoke‑developed index to 450 (when tested per ASTM E84 / UL 723), with specific exceptions and different limits for certain foam plastics and special installations. See §807.1 and §720.2 for the controlling citations.

Requirements in detail

Key rule

Section 807.1: Thermal and acoustical insulation is required to comply with Section 720 (i.e., §720 controls insulation surface‑burning requirements).
Section 720.2 (concealed installations): Insulating materials installed in concealed spaces shall have a flame‑spread index ≤ 25 and a smoke‑developed index ≤ 450 when tested in accordance with ASTM E84 or UL 723, unless a specific exception applies.

Decision‑relevant values (quick reference table)

Application / condition	Flame‑spread index (max)	Smoke‑developed index (max)	Code reference
Insulation — concealed spaces (general)	25	450	§720.2
Insulation — exposed (general)	25	450	§720.3
Pipe/tube insulation & coverings	25	450	§720.7
Loose‑fill insulation (difficult to mount in E84 apparatus) — test method	—	— (use CAN/ULC S102.2 for E84‑like results)	§720.4 (tests per CAN/ULC S102.2)
Cellulosic loose‑fill (exception) — smoke only	(flame spread exemption)	450	§720.2 Exception; §720.6 (labeling/tests)
Foam plastic insulation (general rule, non‑plenum)	75	450	§2603.3 (foam plastic surface‑burning)
Foam plastic in plenums (interior finish / trim)	25	50	§2603.7 (plenums: 25/50 and NFPA 286 requirements)
Reflective plastic‑core insulation (max thickness tested)	25	450	§2614.3

Notes on testing: ASTM E84 / UL 723 are the specified test standards for flame‑spread and smoke‑developed indices in Section 720; where loose‑fill materials cannot be mounted in the E84 apparatus, CAN/ULC S102.2 is specified for testing. §720.1 and §720.4 explain these testing bases.

How the classes map (for interior finishes context)

The CBC groups interior finish materials by flame‑spread/smoke indices (Class A = 0–25 flame, 0–450 smoke; Class B = 26–75 flame; Class C = 76–200 flame) in Chapter 8 — useful for understanding how the 25 limit places insulation in the Class A category for surface burning. See §803.1.2 for the class table.

Exceptions & special cases

Cellulosic fiber loose‑fill insulation that meets the labeling/testing requirements of §720.6 is not required to meet the flame‑spread index requirement but must meet smoke ≤ 450 when tested per CAN/ULC S102.2. (§720.2 Exception; §720.6)
Facings and reflective foils installed behind and in substantial contact with the unexposed surface in concealed spaces of Type III/IV/V construction are excepted from the flame‑spread and smoke limits in §720.2. (§720.2.1)
Roof insulation: combustible roof insulation that doesn’t meet §720.2/720.3 may be used if covered with an approved roof covering directly applied. (§720.5)
Foam plastics: different limits and additional requirements apply (generally flame ≤ 75 / smoke ≤ 450), and stricter or additional tests (thermal barrier, NFPA 286, etc.) apply for certain uses (see §2603 series). (§2603.3, §2603.4, §2603.7)

If a product or installation falls into one of these exceptions, read the specific paragraph cited — the exception language (and referenced test standards) controls compliance.

Common mistakes

Assuming “all insulation” can be treated the same: foam plastics have different limits and additional thermal‑barrier or testing requirements (§2603), so treating foam the same as mineral‑fiber or fiberglass can lead to noncompliance.
Forgetting facings when testing: the code requires that insulation be tested with facings/coverings in place when those are used (§720.1). Tests that omit facings can understate hazard.
Using ASTM E84 results for loose‑fill materials that cannot be mounted in the E84 apparatus without applying the CAN/ULC S102.2 protocol; using the wrong test method invalidates the comparison to the 25/450 limits. (§720.4)
Overlooking pipe/tube insulation requirements: pipe insulation and coverings have the same 25/450 limits unless they are in plenums (see §720.7).

Worked example — concrete scenario with numbers

Situation: You are specifying batt insulation to be installed in a concealed ceiling cavity above an office space (non‑plenum, Type II construction). The manufacturer’s ASTM E84 report shows: flame‑spread = 22; smoke‑developed = 410. Is it code‑compliant?

Step 1 — Applicable rules: §807.1 ties insulation to §720; §720.2 applies because the insulation is concealed. (§807.1; §720.2).

Step 2 — Compare values: §720.2 limits are flame‑spread ≤ 25 and smoke ≤ 450. The product’s tested values are 22 (flame) and 410 (smoke). Both are at or below the limits.

Conclusion: This batt insulation meets the CBC surface‑burning criteria for concealed installation and is acceptable on that basis, unless another exception/requirement applies (facings, construction type exception, or special local amendment).

If the same material were foam plastic with an E84 flame‑spread of 60, you would need to consult §2603 (foam plastic rules) because foam plastics are generally allowed up to flame‑spread 75 in non‑special uses but have additional requirements (thermal barrier, etc.). (§2603.3)

Related provisions (useful nearby CBC sections)

§807.1 — Insulation must comply with Section 720 (ties insulation to §720).
§720.1 — General testing and inclusion of facings in tests (ASTM E84 / UL 723).
§720.3 — Exposed insulation limits (same 25/450 baseline).
§720.4 — Loose‑fill insulation testing rules (CAN/ULC S102.2).
§720.6 — Cellulosic loose‑fill labeling and special compliance path.
§720.7 — Insulation/covering on pipe and tubing.
§2603 (esp. §2603.3, §2603.4, §2603.7) — Foam plastic insulation special limits, thermal barrier and plenum rules.
§2614.3 — Reflective plastic‑core insulation surface‑burning limits.
§803.1.2 — Interior finish class definitions (mapping of flame/smoke indices to Class A/B/C).

Code references

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

CBC § 720.2 High relevance — show source text
720.2 Concealed installation. Insulating materials, where concealed as installed in buildings of any type of construction, shall have a flame spread index of not more than 25 and a smoke-developed index of not more than 450.

Exception: Cellulosic fiber loose-fill insulation complying with the requirements of Section 720.6 shall not be required to meet a flame spread index requirement but shall be required to meet a smoke-developed index of not more than 450 when tested in accordance with CAN/ULC S102.2.

720.2.1 Facings. Where such materials are installed in concealed spaces in buildings of Type III, IV or V construction, the flame spread and smoke-developed limitations do not apply to facings, coverings, and layers of reflective foil insulation that are installed behind and in substantial contact with the unexposed surface of the ceiling, wall or floor finish.

Exception: All layers of single and multilayer reflective plastic core insulation shall comply with Section 2614.

720.3 Exposed installation. Insulating materials, where exposed as installed in buildings of any type of construction, shall have a flame spread index of not more than 25 and a smoke-developed index of not more than 450.

Exception: Cellulosic fiber loose-fill insulation complying with the requirements of Section 720.6 shall not be required to meet a flame spread index requirement but shall be required to meet a smoke-developed index of not more than 450 when tested in accordance with CAN/ULC S102.2.

720.3.1 Attic floors. Exposed insulation materials installed on attic floors shall have a critical radiant flux of not less than 0.12 watt per square centimeter when tested in accordance with ASTM E970.

720.4 Loose-fill insulation. Loose-fill insulation materials that cannot be mounted in the ASTM E84 or UL 723 apparatus without a screen or artificial supports shall comply with the flame spread and smoke-developed limits of Sections 720.2 and 720.3 when tested in accordance with CAN/ULC S102.2.

Exception: Cellulosic fiber loose-fill insulation shall not be required to meet a flame spread index requirement when tested in accordance with CAN/ULC S102.2, provided that such insulation has a smoke-developed index of not more than 450 and complies with the requirements of Section 720.6.

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FIRE AND SMOKE PROTECTION FEATURES

720.5 Roof insulation. The use of combustible roof insulation not complying with Sections 720.2 and 720.3 shall be permitted in any type of construction provided that insulation is covered with approved roof coverings directly applied thereto.

720.6 Cellulosic fiber loose-fill insulation and self-supported spray-applied cellulosic insulation. Cellulosic fiber loose-fill insulation and self-supported spray-applied cellulosic insulation shall comply with CPSC 16 CFR Parts 1209 and 1404. Each package of such insulating material shall be clearly labeled in accordance with CPSC 16 CFR Parts 1209 and 1404.

720.7 Insulation and covering on pipe and tubing. Insulation and covering on pipe and tubing shall have a flame spread index of not more than 25 and a smoke-developed index of not more than 450.
CBC § 719.5 High relevance — show source text
Exception: Solid plaster partitions or where otherwise determined by fire tests.

719.5 Plaster alternatives for concrete. In reinforced concrete construction, gypsum plaster or Portland cement plaster is permitted to be substituted for [1] / 2 inch (12.7 mm) of the required poured concrete protection, except that a minimum thickness of [3] / 8 inch (9.5 mm) of poured concrete shall be provided in reinforced concrete floors and 1 inch (25 mm) in reinforced concrete columns in addition to the plaster finish. The concrete base shall be prepared in accordance with Section 2510.7.

SECTION 720—THERMAL- AND SOUND-INSULATING MATERIALS

720.1 General. Insulating materials shall comply with the requirements of this section. Where a flame spread index or a smokedeveloped index is specified in this section, such index shall be determined in accordance with ASTM E84 or UL 723. Any material that is subject to an increase in flame spread index or smoke-developed index beyond the limits herein established through the effects of age, moisture or other atmospheric conditions shall not be permitted. Insulating materials, when tested in accordance with the requirements of this section, shall include facings, when used, such as vapor retarders, vapor permeable membranes and similar coverings, and all layers of single and multilayer reflective foil insulation and similar materials.

Exceptions:
1. Fiberboard insulation shall comply with Chapter 23.
2. Foam plastic insulation shall comply with Chapter 26.
3. Duct and pipe insulation and duct and pipe coverings and linings in plenums shall comply with the California Mechanical Code.
4. All layers of single and multilayer reflective plastic core insulation shall comply with Section 2614.
720.2 Concealed installation. Insulating materials, where concealed as installed in buildings of any type of construction, shall have a flame spread index of not more than 25 and a smoke-developed index of not more than 450.

Exception: Cellulosic fiber loose-fill insulation complying with the requirements of Section 720.6 shall not be required to meet a flame spread index requirement but shall be required to meet a smoke-developed index of not more than 450 when tested in accordance with CAN/ULC S102.2.

720.2.1 Facings. Where such materials are installed in concealed spaces in buildings of Type III, IV or V construction, the flame spread and smoke-developed limitations do not apply to facings, coverings, and layers of reflective foil insulation that are installed behind and in substantial contact with the unexposed surface of the ceiling, wall or floor finish.

Exception: All layers of single and multilayer reflective plastic core insulation shall comply with Section 2614.

720.3 Exposed installation. Insulating materials, where exposed as installed in buildings of any type of construction, shall have a flame spread index of not more than 25 and a smoke-developed index of not more than 450.

Exception: Cellulosic fiber loose-fill insulation complying with the requirements of Section 720.6 shall not be required to meet a flame spread index requirement but shall be required to meet a smoke-developed index of not more than 450 when tested in accordance with CAN/ULC S102.2.

720.3.1 Attic floors. Exposed insulation materials installed on attic floors shall have a critical radiant flux of not less than 0.12 watt per square centimeter when tested in accordance with ASTM E970.
CBC § 3.5 High relevance — show source text
WARNING - FIRE HAZARD

This product is required to be installed below a minimum 3.5-inch-thick concrete slab on grade.

NOT FOR VERTICAL OR ABOVE-GRADE APPLICATIONS

This product contains NO flame retardants.

Not tested for flame spread or smoke development requirements of the model building codes 2. Each package shall be labeled on at least two sides in red [1] / 2 -text with the following information:

WARNING – COMBUSTIBLE MATERIAL

Keep away from ignition sources.

Maintain code required separation between product storage and structures under construction (minimum 30 feet).

2603.3 Surface-burning characteristics. Unless otherwise indicated in this section, foam plastic insulation and foam plastic cores of manufactured assemblies shall have a flame spread index of not more than 75 and a smoke-developed index of not more than 450 where tested in the maximum thickness intended for use in accordance with ASTM E84 or UL 723. Loose fill-type foam plastic insulation shall be tested as board stock for the flame spread and smoke-developed indices.

Exceptions:
1. Smoke-developed index for interior trim as provided for in Section 2604.2.
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PLASTIC
1. In cold storage buildings, ice plants, food plants, food processing rooms and similar areas, foam plastic insulation where tested in a thickness of 4 inches (102 mm) shall be permitted in a thickness up to 10 inches (254 mm) where the building is equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1. The approved automatic sprinkler system shall be provided in both the room and that part of the building in which the room is located.
2. Foam plastic insulation that is a part of a Class A, B or C roof-covering assembly provided that the assembly with the foam plastic insulation satisfactorily passes NFPA 276 or UL 1256. The smoke-developed index shall not be limited for roof applications.
3. Foam plastic insulation greater than 4 inches (102 mm) in thickness shall have a maximum flame spread index of 75 and a smoke-developed index of 450 where tested at a minimum thickness of 4 inches (102 mm), provided that the end use is approved in accordance with Section 2603.9 using the maximum thickness and density intended for use.
4. Flame spread and smoke-developed indices for foam plastic interior signs in covered and open mall buildings provided that the signs comply with Section 402.6.4. 6. Polystyrene foam insulation boards with a maximum thickness of 2 inches when installed below a minimum 3.5-inch-thick concrete slab on grade.
2603.4 Thermal barrier. Except as provided for in Sections 2603.4.1 and 2603.9, foam plastic shall be separated from the interior of a building by an approved thermal barrier of [1] / 2 -inch (12.7 mm) gypsum wallboard, mass timber or heavy timber in accordance with Section 2304.11 or a material that is tested in accordance with and meets the acceptance criteria of both the Temperature Transmission Fire Test and the Integrity Fire Test of NFPA 275. Combustible concealed spaces shall comply with Section 718.
California Building Code High relevance — show source text
(f) Mineral aggregate in board form.
1. Composition. The basic material shall be mineral in nature, crushed, dried and graded to the proper particle size and expanded by the application of heat to form a spherical, cellular type of aggregate. It shall be composed of spherical cellular beads of expanded aggregate and fibers formed into rigid, flat, rectangular units and shall have an integral water proofing
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STANDARDS FOR INSULATING MATERIAL

treatment. It shall be clean, dry and free of extraneous material. Fibers shall be evenly distributed and insulation and facings shall be sufficiently coherent to be unaffected by handling and installation. 2. Thermal performance. Determination of the thermal performance shall be in accordance with ANSI/ASTM C177-76, ANSI/ASTM C236-66 or ANSI/ASTM C518-76 at the manufacturer’s option. 3. Resistance to combustion. Surface-burning characteristics of materials with facings and membranes intended for exposed applications shall be determined according to ANSI/ASTM E84-79 and shall not exceed the following values:

Flame spread. . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Smoke developed. . . . . . . . . . . . . . . . . . . . . . 450 Facings and membranes of materials intended for exposed applications shall be exposed to the flame during the ANSI/ASTM E84-79 test.

Insulation boards exclusive of facings and membranes shall not exceed the following values:

Flame spread. . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Smoke developed. . . . . . . . . . . . . . . . . . . . . . . 50 (g) Mineral fiber in blanket form.
1. Composition. The basic material shall be fibers made from mineral substances such as rock, slag or glass processes from a molten state into fibrous form.
2. Thermal performance. Determination of the thermal performance shall be in accordance with ANSI/ASTM C177-76, ANSI/ASTM C236-66 or ANSI/ASTM C518-76 at the manufacturer’s option.
3. Size. The thickness shall be determined according to ANSI/ASTM C167-64.
4. Resistance to combustion. Surface-burning characteristics of materials with facings and membranes intended for exposed applications shall be determined according to ANSI/ASTM E84-79 and shall not exceed the following values:
Flame spread. . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Smoke developed. . . . . . . . . . . . . . . . . . . . . . 450 Facings and membranes of materials intended for exposed applications shall be exposed to the flame during the ANSI/ASTM E84-79 test.

Insulation blankets not intended for exposed applications shall comply with the United States General Services Administration insulation standard HH-I-521F dated September 4, 1980, for flammability and smoldering combustion testing. 5. Corrosiveness. Corrosiveness shall be determined according to Test Description Number 2. The steel test plate in contact with the insulation shall show no greater corrosion than a steel plate in contact with sterile cotton. 6.
California Building Code High relevance — show source text
Minimum space between layers of a multilayer sheet shall conform with the United States General Services Administration insulation standard HH-I-1252B dated August 18, 1976. 4. Resistance to combustion. Surface-burning characteristics shall be determined according to the ANSI/ ASTM E84-79, and shall not exceed the following values:

Flame spread. . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Smoke developed. . . . . . . . . . . . . . . . . . . . . . . 50 5. Pliability. Foil shall be folded and the folded edge smoothed using a light finger pressure. The finished insulation shall not crack when folded to 180° bend at a temperature of 70° ± 2°F and a relative humidity of 50 ± 5 percent. (c) Cellular glass in board form.
1. Composition. The material shall consist of a glass composition which has been foamed or cellulated under molten conditions, annealed and set to form a rigid material with hermetically sealed cells.
2. Thermal performance. Determination of the thermal performance shall be based on a representative sample and shall be in accordance with ANSI/ASTM C177-76, ANSI/ASTM C236-66 or ANSI/ASTM C518-76 at the manufacturer’s option.
3. Resistance to combustion. Surface-burning characteristics shall be determined according to ANSI/ASTM E84-79, and shall not exceed the following values:
Flame spread. . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Smoke developed. . . . . . . . . . . . . . . . . . . . . . . 50 (d) Cellulose fiber in loose fill form.
1. Composition. The basic material shall consist of virgin or recycled wood-based cellulosic fiber and may be made from related paper or paperboard stock, excluding contaminated materials and extraneous foreign materials such as metals and glass which
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STANDARDS FOR INSULATING MATERIAL

may reasonably be expected to be retained in the finished product. Suitable chemicals may be introduced to improve flame resistance, processing and handling characteristics. The particles shall not be so fine as to create a dust hazard, and the added chemicals shall not create a health hazard. The materials used must be capable of proper adhesion to the additive chemicals. 2. Thermal performance. Determination of the thermal performance shall be in accordance with ANSI/ASTM C177-76, ANSI/ASTM C236-66 or ANSI/ASTM C518-76 at the manufacturer’s option. 3. Density. The density shall be determined according to the United States General Services Administration insulation standard HH-I-515D dated June 15, 1978, or as amended October 11, 1979, at the manufacturer’s option.
CBC § 1409.7.1 High relevance — show source text
1409.7.1 Surface-burning characteristics. Unless otherwise specified in this section, a combustible core 4 inches (102 mm) or less in thickness shall have a flame spread index of 75 or less and a smoke-developed index of 450 or less when tested in the maximum thickness intended for use in accordance with ASTM E84 or UL 723. For thicknesses greater than 4 inches (102 mm), the combustible core shall have a flame spread index of 75 or less and a smoke-developed index of 450 or less at 4 inches (102 mm) in thickness and the IMP approved based on testing in accordance with Section 1409.7.2.2 at the maximum IMP thickness intended for use.

1409.7.1.1 Foam plastic core. For IMP having a core insulation composed of foam plastic, the insulation core shall comply with Section 2603.3.

1409.7.2 Thermal barrier. Unless otherwise specified in this section, IMP with a combustible core shall be separated from the interior of a building by an approved thermal barrier consisting of [1] / 2 -inch (12.7 mm) gypsum wallboard or a material that is tested in accordance with and meets the acceptance criteria of both the Temperature Transmission Fire Test and the Integrity Fire Test of NFPA 275.

1409.7.2.1 Foam plastic core. For IMP having a foam plastic core, use with the thermal barrier prescribed in Section 1409.7.2 shall be in accordance with Section 2603.4 unless special approval is obtained on the basis of Section 2603.9.

1409.7.2.2 Special approval. The thermal barrier specified in Section 1409.7.2 is not required where IMP is specifically approved based on tests conducted in accordance with, but not limited to, NFPA 286 (with the acceptance criteria of Section 803.1.1.1), FM 4880 or UL 1715. Such testing shall be performed with the IMP in a configuration related to the actual end-use and at the maximum thickness intended for use, and shall include seams, factory joints, sealants and other typical details intended for use.

1409.7.3 Type I, II, III, and IV construction. Where used as exterior walls or as exterior wall coverings on buildings of Type I, II, III and IV construction, IMP systems shall comply with this section as follows:
1. IMP having a foam plastic core shall comply with Section 2603.5.
2. IMP having combustible core other than foam plastic shall comply with Sections 1409.7.3.1 through 1409.7.3.4.
1409.7.3.1 Surface-burning characteristics. A combustible core not greater than 4 inches (102 mm) in thickness shall have a flame spread index of 25 or less and a smoke-developed index of 450 or less when tested in the maximum thickness intended for use in accordance with ASTM E84 or UL 723. For thicknesses greater than 4 inches (102 mm) the combustible core shall have a flame spread index of 75 or less and a smoke-developed index of 450 or less at 4 inches (102 mm) in thickness and the IMP approved based on testing in accordance with Section 1409.7.2.2 at the maximum IMP thickness intended for use.

1409.7.3.2 Thermal barrier. IMP shall be separated from the interior of a building by an approved thermal barrier in accordance with Section 1409.7.2.
CBC § 9.4.1 High relevance — show source text
1. The peak heat release rate throughout the test shall not exceed 800 kW.
2. The total smoke released throughout the test shall not exceed 1,000 m [2] .
R302.9.4.1 Stability. Interior finish materials regulated by this chapter shall be applied or otherwise fastened in such a manner that such materials will not readily become detached where subjected to room temperatures of 200°F (93°C) for not less than 30 minutes.

R302.9.5 High-density polyethylene (HDPE) and polypropylene (PP). Where high-density polyethylene or polypropylene is used as an interior finish material, it shall be tested in accordance with NFPA 286 and comply with the criteria in Section R302.9.4.

R302.10 Flame spread index and smoke-developed index for insulation. Flame spread and smoke-developed index for insulation shall be in accordance with Sections R302.10.1 through R302.10.4.

R302.10.1 Insulation. Insulating materials installed within floor-ceiling assemblies, roof-ceiling assemblies, wall assemblies, crawl spaces and attics shall comply with the requirements of this section. They shall exhibit a flame spread index not to exceed 25 and a smoke-developed index not to exceed 450 where tested in accordance with ASTM E84 or UL 723. Insulating materials, where tested in accordance with the requirements of this section, shall include facings, where used, such as vapor retarders, vapor permeable membranes and similar coverings.

Exceptions:
1. Where such materials are installed in concealed spaces, the flame spread index and smoke-developed index limitations do not apply to the facings, provided that the facing is installed in substantial contact with the unexposed surface of the ceiling, floor or wall finish.
2. Cellulose fiber loose-fill insulation that is not spray applied and that complies with the requirements of Section R302.10.3 shall not be required to meet the flame spread index requirements but shall be required to meet a smokedeveloped index of not more than 450 where tested in accordance with CAN/ULC S102.2.
3. Foam plastic insulation shall comply with Section R303.
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BUILDING PLANNING

R302.10.2 Loose-fill insulation. Loose-fill insulation materials that cannot be mounted in the ASTM E84 or UL 723 apparatus without a screen or artificial supports shall comply with the flame spread and smoke-developed limits of Section R302.10.1 where tested in accordance with CAN/ULC S102.2.

Exception: Cellulosic fiber loose-fill insulation shall not be required to be tested in accordance with CAN/ULC S102.2, provided that such insulation complies with the requirements of Sections R302.10.1 and R302.10.3.

R302.10.3 Cellulosic fiber loose-fill insulation. Cellulosic fiber loose-fill insulation shall comply with CPSC 16 CFR, Parts 1209 and 1404. Each package of such insulating material shall be clearly labeled in accordance with CPSC 16 CFR, Parts 1209 and 1404.

R302.10.4 Exposed attic insulation. Exposed insulation materials installed on attic floors shall have a critical radiant flux of not less than 0.12 watt per square centimeter when tested in accordance with ASTM E970.
CBC § 9.1 High relevance — show source text
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.
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] .
R302.9.4.1 Stability. Interior finish materials regulated by this chapter shall be applied or otherwise fastened in such a manner that such materials will not readily become detached where subjected to room temperatures of 200°F (93°C) for not less than 30 minutes.

R302.9.5 High-density polyethylene (HDPE) and polypropylene (PP). Where high-density polyethylene or polypropylene is used as an interior finish material, it shall be tested in accordance with NFPA 286 and comply with the criteria in Section R302.9.4.

R302.10 Flame spread index and smoke-developed index for insulation. Flame spread and smoke-developed index for insulation shall be in accordance with Sections R302.10.1 through R302.10.4.

R302.10.1 Insulation. Insulating materials installed within floor-ceiling assemblies, roof-ceiling assemblies, wall assemblies, crawl spaces and attics shall comply with the requirements of this section. They shall exhibit a flame spread index not to exceed 25 and a smoke-developed index not to exceed 450 where tested in accordance with ASTM E84 or UL 723. Insulating materials, where tested in accordance with the requirements of this section, shall include facings, where used, such as vapor retarders, vapor permeable membranes and similar coverings.

Exceptions:

CBC § 720.4 High relevance — show source text

720.4 Loose-fill insulation. Loose-fill insulation materials that cannot be mounted in the ASTM E84 or UL 723 apparatus without a screen or artificial supports shall comply with the flame spread and smoke-developed limits of Sections 720.2 and 720.3 when tested in accordance with CAN/ULC S102.2.

Exception: Cellulosic fiber loose-fill insulation shall not be required to meet a flame spread index requirement when tested in accordance with CAN/ULC S102.2, provided that such insulation has a smoke-developed index of not more than 450 and complies with the requirements of Section 720.6.

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720.5 Roof insulation. The use of combustible roof insulation not complying with Sections 720.2 and 720.3 shall be permitted in any type of construction provided that insulation is covered with approved roof coverings directly applied thereto.

720.6 Cellulosic fiber loose-fill insulation and self-supported spray-applied cellulosic insulation. Cellulosic fiber loose-fill insulation and self-supported spray-applied cellulosic insulation shall comply with CPSC 16 CFR Parts 1209 and 1404. Each package of such insulating material shall be clearly labeled in accordance with CPSC 16 CFR Parts 1209 and 1404.

720.7 Insulation and covering on pipe and tubing. Insulation and covering on pipe and tubing shall have a flame spread index of not more than 25 and a smoke-developed index of not more than 450.

Exception: Insulation and covering on pipe and tubing installed in plenums shall comply with the California Mechanical Code .

SECTION 721—PRESCRIPTIVE FIRE RESISTANCE

721.1 General. The provisions of this section contain prescriptive details of fire-resistance-rated building elements, components or assemblies. The materials of construction specified in Tables 721.1(1), 721.1(2) and 721.1(3) shall be assumed to have the fire-resistance ratings prescribed therein. Where materials that change the capacity for heat dissipation are incorporated into a fireresistance-rated assembly, fire test results or other substantiating data shall be made available to the building official to show that the required fire-resistance-rating time period is not reduced.

TABLE 721.1(1)—MINIMUM PROTECTION OF STRUCTURAL PARTS BASED ON TIME PERIODS FOR VARIOUS NONCOMBUSTIBLE INSULATING MATERIALSm	Col2	Col3	Col4	Col5	Col6	Col7
STRUCTURAL PARTS TO BE PROTECTED	ITEM NUMBER	INSULATING MATERIAL USED	MINIMUM THICKNESS OF INSULATING MATERIAL FOR THE FOLLOWING FIRE-RESISTANCE PERIODS (inches)	MINIMUM THICKNESS OF INSULATING MATERIAL FOR THE FOLLOWING FIRE-RESISTANCE PERIODS (inches)	MINIMUM THICKNESS OF INSULATING MATERIAL FOR THE FOLLOWING FIRE-RESISTANCE PERIODS (inches)	MINIMUM THICKNESS OF INSULATING MATERIAL **FOR THE FOLLOWING FIRE-RESISTANCE

CBC § 720.7. High relevance — show source text
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

FIRE AND SMOKE PROTECTION FEATURES
1. Combustible piping within partitions or shaft enclosures installed in accordance with the provisions of this code.
2. Combustible piping within concealed ceiling spaces installed in accordance with the California Mechanical Code and the California Plumbing Code .
3. Combustible insulation and covering on pipe and tubing, installed in concealed spaces other than plenums, complying with Section 720.7.
SECTION 719—FIRE-RESISTANCE REQUIREMENTS FOR PLASTER

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

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

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

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

719.5 Plaster alternatives for concrete. In reinforced concrete construction, gypsum plaster or Portland cement plaster is permitted to be substituted for [1] / 2 inch (12.7 mm) of the required poured concrete protection, except that a minimum thickness of [3] / 8 inch (9.5 mm) of poured concrete shall be provided in reinforced concrete floors and 1 inch (25 mm) in reinforced concrete columns in addition to the plaster finish. The concrete base shall be prepared in accordance with Section 2510.7.

SECTION 720—THERMAL- AND SOUND-INSULATING MATERIALS

720.1 General. Insulating materials shall comply with the requirements of this section. Where a flame spread index or a smokedeveloped index is specified in this section, such index shall be determined in accordance with ASTM E84 or UL 723. Any material that is subject to an increase in flame spread index or smoke-developed index beyond the limits herein established through the effects of age, moisture or other atmospheric conditions shall not be permitted. Insulating materials, when tested in accordance with the requirements of this section, shall include facings, when used, such as vapor retarders, vapor permeable membranes and similar coverings, and all layers of single and multilayer reflective foil insulation and similar materials.

Exceptions:
1. Fiberboard insulation shall comply with Chapter 23.
2. Foam plastic insulation shall comply with Chapter 26.
3. Duct and pipe insulation and duct and pipe coverings and linings in plenums shall comply with the California Mechanical Code.
4. All layers of single and multilayer reflective plastic core insulation shall comply with Section 2614.
CBC § 3.1 High relevance — show source text
R303.3 Surface burning characteristics. Unless otherwise allowed in Section R303.5, foam plastic, or foam plastic cores used as a component in manufactured assemblies, used in building construction shall comply with Section R303.3.1 or R303.3.2. Loose-filltype foam plastic insulation shall be tested as board stock for the flame spread index and smoke-developed index.

Exception s: 1. Spray foam plastic insulation more than 4 inches (102 mm) in thickness shall have a flame spread index of not more than 25 and a smoke-developed index of not more than 450 where tested at a thickness of 4 inches (102 mm) and at the density intended for use. Such spray foam plastic shall be separated from the interior of a building by [1] / 2 -inch (12.7 mm)

2025 CALIFORNIA RESIDENTIAL CODE 3-31

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BUILDING PLANNING

gypsum wallboard or by a material that is tested in accordance with and meets the acceptance criteria of both the Temperature Transmission Fire Test and the Integrity Fire Test of NFPA 275. 2. Polystyrene foam insulation boards with a maximum thickness of 2 inches where installed below a minimum 3.5-inch thick concrete slab on grade.

R303.3.1 Foam plastic insulation 4 inches thick or less. Foam plastic insulation installed at 4 inches (102 mm) in thickness or less shall have a flame spread index of not more than 75 and a smoke-developed index of not more than 450 where tested in the maximum thickness and density intended for use in accordance with ASTM E84 or UL 723.

R303.3.2 Foam plastic insulation more than 4 inches thick. Foam plastic insulation installed at more than 4 inches (102 mm) in thickness shall have a flame spread index of not more than 75 and a smoke-developed index of not more than 450 where tested at a thickness of 4 inches (102 mm) in accordance with ASTM E84 or UL 723, provided that the end use is approved in accordance with Section R303.6 using the thickness and density intended for use.

R303.4 Thermal barrier. Unless otherwise allowed in Section R303.5, foam plastic shall be separated from the interior of a building by an approved thermal barrier of not less than [1] / 2 -inch (12.7 mm) gypsum wallboard, [23] / 32 -inch (18.2 mm) wood structural panel or a material that is tested in accordance with and meets the acceptance criteria of both the Temperature Transmission Fire Test and the Integrity Fire Test of NFPA 275.

R303.5 Specific requirements. The following requirements shall apply to these uses of foam plastic unless specifically approved in accordance with Section R303.6 or by other sections of the code or the requirements of Sections R303.2 through R303.4 have been met.

R303.5.1 Masonry or concrete construction. The thermal barrier specified in Section R303.4 is not required in a masonry or concrete wall, floor or roof where the foam plastic insulation is separated from the interior of the building by not less than a 1-inch (25 mm) thickness of masonry or concrete.
CBC § 2.2. High relevance — show source text
PLASTIC

2.2. Where the fire separation distance is 5 feet (1524 mm) or less, the area of the fiber-reinforced polymer shall not exceed 10 percent of the wall area. Where the fire separation distance is greater than 5 feet (1524 mm), the area of the exterior wall coverage using fiber-reinforced polymer shall not be limited. 2.3. The fiber-reinforced polymer shall have a flame spread index of 200 or less. The flame spread index requirements do not apply to coatings or paints having a thickness of less than 0.036 inch (0.9 mm) that are applied directly to the surface of the fiber-reinforced polymer. 2.4. Fireblocking complying with Section 718.2.6 shall be installed.

SECTION 2614—REFLECTIVE PLASTIC CORE INSULATION

2614.1 General. The provisions of this section shall govern the requirements and uses of reflective plastic core insulation in buildings and structures. Reflective plastic core insulation shall comply with the requirements of Section 2614 and of Section 2614.3 or 2614.4.

2614.2 Identification. Packages and containers of reflective plastic core insulation delivered to the job site shall show the manufacturer’s or supplier’s name, product identification and information sufficient to determine that the end use will comply with the code requirements.

2614.3 Surface-burning characteristics. Reflective plastic core insulation shall have a flame spread index of not more than 25 and a smoke-developed index of not more than 450 when tested in accordance with ASTM E84 or UL 723. The reflective plastic core insulation shall be tested at the maximum thickness intended for use. Test specimen preparation and mounting shall be in accordance with ASTM E2599.

2614.4 Room corner test heat release. Reflective plastic core insulation shall comply with the acceptance criteria of Section 803.1.1.1 when tested in accordance with NFPA 286 or UL 1715 in the manner intended for use and at the maximum thickness

intended for use.

2025 CALIFORNIA BUILDING CODE 26-13

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

26-14 2025 CALIFORNIA BUILDING CODE

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

CALIFORNIA BUILDING CODE – MATRIX ADOPTION TABLE

CHAPTER 27 – ELECTRICAL

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

Frequently asked questions

Do I always need an ASTM E84 report for insulation?

Yes — Section 720 specifies that flame‑spread and smoke indices are to be determined per ASTM E84 or UL 723; where loose‑fill cannot be mounted in that apparatus, CAN/ULC S102.2 is specified. (§720.1, §720.4).

Can cellulosic loose‑fill insulation skip flame‑spread testing?

Cellulosic fiber loose‑fill that complies with §720.6 is exempt from the flame‑spread index requirement but must meet smoke‑developed ≤ 450 when tested per CAN/ULC S102.2 and meet the labeling/testing requirements. (§720.2 Exception; §720.6).

Are foam plastics treated the same as other insulation?

No. Foam plastics have their own surface‑burning limits and additional requirements (generally flame‑spread ≤ 75 / smoke ≤ 450 for common uses), and stricter limits or thermal barriers apply in certain situations (e.g., plenums, interior finishes). See §2603.

If an insulation product has facings, do test results have to include the facing?

Yes. §720.1 requires insulating materials to be tested with facings/coverings in place when such facings are used in the installed product.

What if my installation is under a roof cover or in a roof assembly?

Combustible roof insulation that does not meet the §720 limits is permitted provided it is covered with approved roof coverings directly applied thereto (see §720.5).

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