CBC · California Building Code

What materials are allowed in concealed spaces of Types I and II buildings?

In Type I and II buildings the CBC generally forbids combustible materials in concealed spaces (§ 718.5), but allows a few narrowly defined items and conditions per § 603 (for example certain fire‑retardant wood uses, insulation meeting flame‑spread limits, and service piping/wiring when installed per trade codes). Where combustible items remain the building must meet specific protections (sprinklers in the concealed space, noncombustible fill, or 5/8‑inch Type X gypsum sheathing) as prescribed in § 602.4.4.3; always read § 718.5 together with § 603.1 and the referenced mechanical, plumbing and electrical provisions filefile.

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Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

The CBC generally prohibits combustible materials in concealed spaces of Type I and II buildings: “Combustible materials shall not be permitted in concealed spaces of buildings of Type I or II construction” (§ 718.5) . Limited, specific exceptions are provided by Section 603 (see § 603.1 and its subsections), and some mechanical/electrical/plumbing items are allowed when installed in accordance with the respective trade codes (§ 603.1, § 718.5) . Where combustible elements remain in a concealed space the CBC requires protective measures (for example sprinklers, filling with noncombustible insulation, or sheathing with 5/8‑inch Type X gypsum) per the Types‑of‑Construction provisions (§ 602.4.4.3) .

Requirements in detail

Broad prohibition and how to read it

  • The baseline rule: no combustible materials in concealed spaces of Type I/II buildings (§ 718.5) .
  • The prohibition is not absolute — Section 718.5 points to specific allowances in Section 603 and to regulated plenums and finish materials; those allowances must be read narrowly and in context (§ 718.5, § 603.1) .

What Section 603 permits (high level)

Section 603.1 lists limited combustible materials and conditions that are permitted in Type I and II construction. The most used allowances are:

  • Fire‑retardant‑treated wood (FRTW) allowed in specified nonbearing partitions, some exterior walls, roofing elements and certain balcony/deck elements — subject to the enumerated conditions and exceptions in § 603.1.1 .
  • Thermal and acoustical insulation (other than foam plastics) with flame spread index ≤ 25, with several narrowly stated exceptions allowing higher indices in special configurations (§ 603.1.2) .
  • Combustible service items installed per the trade codes: nonmetallic ducts per the California Mechanical Code (§ 603.1.1), combustible piping per the Mechanical and Plumbing Codes (§ 603.1.2), and electrical wiring methods with combustible insulation where allowed by the California Electrical Code (§ 603.1.3) .

How Types‑of‑Construction protections interact

Even where Section 603 allows combustible items, concealed spaces in Types I/II often must be protected by one or more measures: automatic sprinklers throughout (with sprinklers in the concealed spaces), completely filling the space with noncombustible insulation, or fully sheathing combustible surfaces with not less than 5/8‑inch Type X gypsum board (§ 602.4.4.3) .

Fireblocking/draftstopping and limits that matter for concealed spaces

Concealed spaces in combustible construction require fireblocking or draftstops per Chapter 7 rules. Examples:

  • Fireblocking materials enumerated by the CBC include 2‑inch nominal lumber, 1/2‑inch gypsum board, mineral wool batts, cellulose tested for the application, and other listed materials (§ 718.2.1) .
  • Vertical and horizontal fireblocking locations: e.g., horizontal fireblocking in walls at intervals not exceeding 10 ft (§ 718.2.2) .
  • Draftstops subdivide floor/ceiling spaces (typically to ≤ 1,000 ft²) and attics/roof concealed spaces (typically to ≤ 3,000 ft²), unless the building is fully sprinklered (§ 718.3, § 718.4) .

Decision‑relevant dimensions / values (quick reference)

Material / condition Allowed? Key limits / values Code reference
General combustible materials in concealed spaces No (baseline) Prohibited except as allowed by § 603 or listed exceptions § 718.5
Fire‑retardant‑treated wood (FRTW) Yes — limited uses Nonbearing partitions ≤ 2‑hr rating, some exterior walls, roof members, balconies on ≤3‑story buildings; see exceptions in § 603.1.1 § 603.1.1
Thermal/acoustical insulation (non‑foam) Yes Flame spread index ≤ 25; exceptions allow ≤100 between two noncombustible layers or ≤200 under solid decking (see § 603.1.2) § 603.1.2
Nonmetallic ducts Yes (when installed per mechanical code) Subject to California Mechanical Code limitations § 603.1.1
Combustible piping in concealed spaces Yes (limited) Must comply with Cal. Mechanical / Plumbing Codes; some piping within partitions/shafts allowed per exceptions in § 718.5 § 603.1.2; § 718.5 exceptions
Protection where combustible surfaces remain in concealed space Required Provide sprinklers in the concealed space, or fill with noncombustible insulation, or sheath combustible surfaces with ≥5/8‑in Type X gypsum § 602.4.4.3
Fireblocking horizontal interval in stud walls N/A (fireblocking rule) Horizontal fireblocking ≤ 10 ft intervals § 718.2.2
Draftstopping floor/ceiling spaces N/A (draftstop rule) Subdivide so horizontal floor areas ≤ 1,000 ft² (attics 3,000 ft²) unless sprinkled § 718.3, § 718.4

(Each “Allowed?” entry above must be interpreted together with the full text of the cited CBC section and the applicable trade codes.)

Exceptions & special cases

  • Section 718.5 lists the baseline prohibition and then allows specific exceptions, primarily: combustible materials allowed in accordance with Section 603; combustible materials exposed within plenums that comply with the California Mechanical Code; and Class A interior finish materials classified under Section 803 — but these are narrow exceptions and not carte blanche permissions (§ 718.5) .
  • Section 603.1 contains numerous sub‑exceptions (for example, limits on FRTW in certain roof locations, and special conditions for insulation flame spread) that must be followed precisely (§ 603.1) .
  • Even where Section 603 permits an item (e.g., nonmetallic ducts, combustible piping, electrical wiring insulation), those items must be installed in accordance with the California Mechanical, Plumbing or Electrical Codes as applicable (§ 603.1.1–.3) .
  • Types‑of‑Construction rules (§ 602.4.4.3) add mandatory protective measures where combustible surfaces or components occur in concealed spaces of Types I/II buildings (sprinklers in the space, fill with noncombustible insulation, or sheath with 5/8‑in Type X gypsum) — follow the specific option chosen and the referenced sprinkler and construction sections (§ 602.4.4.3) .

Common mistakes

  • Treating § 718.5 as permissive rather than prohibitive: people sometimes assume “Section 718.5 lists what’s allowed” — in fact it starts with a prohibition and points to narrow exceptions in § 603 and other specific rules (§ 718.5) .
  • Installing combustible insulation or foam without checking flame‑spread limits or Chapter 26 requirements — foam plastics are regulated separately and have additional restrictions (§ 603.1.2; Chapter 26 reference) .
  • Forgetting trade‑code limitations: nonmetallic ducts, combustible piping or wiring methods are allowed only when installed per the California Mechanical, Plumbing or Electrical Codes — compliance with those codes is required (§ 603.1.1–.3) .
  • Overlooking required protection options in § 602.4.4.3 when combustible surfaces remain in concealed spaces (sprinklers, noncombustible insulation fill, or 5/8‑in Type X sheathing) .
  • Applying allowances for floor/attic draftstopping incorrectly — draftstop and fireblocking area/interval limits (1,000 ft², 3,000 ft², 10‑ft horizontal intervals) are frequently misapplied when the building is not fully sprinklered (§ 718.2–.4) file.

Worked example

Scenario: You are designing a Type IIA office building (nonsprinklered attic/concealed roof space) and need to run service piping and install thermal insulation in the concealed roof space under the roof deck. Can you use combustible piping and standard fiberglass batt insulation?

Step 1 — baseline prohibition: § 718.5 prohibits combustible materials in concealed spaces of Type I/II construction, so the default is “no” unless an exception applies (§ 718.5) .
Step 2 — check Section 603 exceptions: combustible piping is permitted where installed in accordance with the Mechanical/Plumbing Codes (§ 603.1.2); thermal insulation (non‑foam) is permitted if its flame spread index ≤ 25 unless an exception applies (§ 603.1.2) file. So piping may be allowed, and batt insulation may be allowed only if it meets the flame spread limit.
Step 3 — address the unsprinklered concealed space: § 602.4.4.3 requires that concealed spaces either be sprinklered, completely filled with noncombustible insulation, or that combustible surfaces be fully sheathed with not less than 5/8‑in Type X gypsum board. Because the attic is not sprinklered and you propose combustible insulation and piping, you must either (a) change to noncombustible insulation fill, (b) sheath combustible surfaces with 5/8‑in Type X gypsum, or (c) provide sprinklers and sprinkler protection within the concealed space (§ 602.4.4.3) .
Conclusion: You may install combustible piping only if it meets the trade‑code installation requirements, and you may use non‑foam batt insulation only if it meets the flame spread criteria — but because the concealed attic is unsprinklered you must also choose one of the protective measures in § 602.4.4.3 (e.g., sheath the underside of the roof decking and joists with 5/8‑in Type X gypsum) to comply filefile.

Related provisions

  • § 718.5 — Combustible materials in concealed spaces in Type I or II construction (baseline prohibition and exceptions)
  • § 603 and § 603.1 — Combustible material allowances in Types I and II construction (detailed permitted items and limits)
  • § 602.4.4.3 — Concealed spaces protections in Type IV/roof/assembly provisions (sprinkler, noncombustible fill, 5/8‑in Type X sheathing) — used by Types I/II when combustible surfaces are present
  • § 718.2 — Fireblocking materials and locations (lists acceptable fireblock materials)
  • § 718.3, § 718.4 — Draftstopping requirements for floors and attics (area limits and materials)
  • § 603.1.1–.3 — Specific trade exceptions (ducts, piping, electrical) and references to the California Mechanical/Plumbing/Electrical Codes
  • § 803 — Interior finish classifications (Class A finish referenced as an exception in § 718.5)
  • § 720.7 — Requirements for combustible insulation and covering on pipe (referenced in § 718.5 exceptions)

Code references

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

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

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

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

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    TYPES OF CONSTRUCTION

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

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

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

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

    SECTION 603—COMBUSTIBLE MATERIAL IN TYPES I AND II CONSTRUCTION

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

    1. Fire-retardant-treated wood complying with Section 2303.2 shall be permitted in: 1.1. Nonbearing partitions where the required fire-resistance rating is 2 hours or less except in shaft enclosures within Group I-2 occupancies and ambulatory care facilities. 1.2. Nonbearing exterior walls where fire-resistance-rated construction is not required. 1.3. Roof construction, including girders, trusses, framing and decking. Exceptions:
    2. In buildings of Type IA construction exceeding two stories above grade plane, fire-retardant-treated wood is not permitted in roof construction where the vertical distance from the upper floor to the roof is less than 20 feet (6096 mm).
    3. Group I-2, roof construction containing fire-retardant-treated wood shall be covered by not less than a Class A roof covering or roof assembly, and the roof assembly shall have a fire-resistance rating where required by the construction type. 1.4. Balconies, porches, decks and exterior stairways not used as required exits on buildings three stories or less above grade plane.
    4. Thermal and acoustical insulation, other than foam plastics, having a flame spread index of not more than 25. Exceptions:
    5. Insulation placed between two layers of noncombustible materials without an intervening airspace shall be allowed to have a flame spread index of not more than 100.
    6. Insulation installed between a finished floor and solid decking without intervening airspace shall be allowed to have a flame spread index of not more than 200.
    7. Foam plastics in accordance with Chapter 26.
  • CBC § 717.7 High relevance — show source text

    1. A shaft enclosure in accordance with Section 713.

    2. The duct connects not more than two stories, and the annular space around the penetrating duct is protected with an approved noncombustible material that resists the free passage of flame and the products of combustion.

    3. In floor assemblies composed of noncombustible materials, a shaft shall not be required where the duct connects not more than three stories, the annular space around the penetrating duct is protected with an approved noncombustible material that resists the free passage of flame and the products of combustion and a fire damper is installed at each floor line. Exception: Fire dampers are not required in ducts within individual residential dwelling units.

    717.7 Flexible ducts and air connectors. Flexible ducts and air connectors shall not pass through any fire-resistance-rated assembly. Flexible air connectors shall not pass through any wall, floor or ceiling.

    SECTION 718—CONCEALED SPACES

    718.1 General. Fireblocking and draftstops shall be installed in combustible concealed locations in accordance with this section. Fireblocking shall comply with Section 718.2. Draftstops in floor/ceiling spaces and attic spaces shall comply with Sections 718.3 and 718.4, respectively. The permitted use of combustible materials in concealed spaces of buildings of Type I or II construction shall be limited to the applications indicated in Section 718.5.

    718.2 Fireblocking. In combustible construction, fireblocking shall be installed to cut off concealed draft openings (both vertical and horizontal) and shall form an effective barrier between floors, between a top story and a roof or attic space. Fireblocking shall be installed in the locations specified in Sections 718.2.2 through 718.2.7.

    718.2.1 Fireblocking materials. Fireblocking shall consist of the following materials:

    1. Two-inch (51 mm) nominal lumber.

    2. Two thicknesses of 1-inch (25 mm) nominal lumber with broken lap joints.

    3. One thickness of 0.719-inch (18.3 mm) wood structural panels with joints backed by 0.719-inch (18.3 mm) wood structural panels.

    4. One thickness of 0.75-inch (19.1 mm) particleboard with joints backed by 0.75-inch (19 mm) particleboard.

    5. One-half-inch (12.7 mm) gypsum board.

    6. One-fourth-inch (6.4 mm) cement-based millboard.

    7. Batts or blankets of mineral wool, mineral fiber or other approved materials installed in such a manner as to be securely retained in place.

    8. Cellulose insulation tested in the form and manner intended for use to demonstrate its ability to remain in place and to retard the spread of fire and hot gases.

    9. Mass timber complying with Section 2304.11.

    10. One thickness of [19] / 32 -inch (15.1 mm) fire-retardant-treated wood structural panel complying with Section 2303.2.

    718.2.1.1 Batts or blankets of mineral wool or mineral fiber. Batts or blankets of mineral wool or mineral fiber or other approved nonrigid materials shall be permitted for compliance with the 10-foot (3048 mm) horizontal fireblocking in walls constructed using parallel rows of studs or staggered studs.

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

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    TYPES OF CONSTRUCTION

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

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

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

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

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    CALIFORNIA BUILDING CODE – MATRIX ADOPTION TABLE

    CHAPTER 7 – FIRE AND SMOKE PROTECTION FEATURES

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

  • CBC § 0.019 High relevance — show source text

    Aluminum having a minimum thickness of 0.019 inch (0.5 mm). 2.2. Corrosion-resistant steel having a base metal thickness not less than 0.016 inch (0.4 mm) at any point. 2.3. Other approved noncombustible materials. 3. Fireblocking shall not be required where the exterior wall covering has been tested in accordance with, and complies with the acceptance criteria of, NFPA 285. The exterior wall covering shall be installed as tested in accordance with NFPA 285.

    718.2.7 Concealed sleeper spaces. Where wood sleepers are used for laying wood flooring on masonry or concrete fire-resistance-rated floors, the space between the floor slab and the underside of the wood flooring shall be filled with an approved material to resist the free passage of flame and products of combustion or fireblocked in such a manner that open spaces under the flooring shall not exceed 100 square feet (9.3 m [2] ) in area and such space shall be filled solidly under permanent partitions so that communication under the flooring between adjoining rooms shall not occur.

    Exceptions:

    1. Fireblocking is not required for slab-on-grade floors in gymnasiums.
    2. Fireblocking is required only at the juncture of each alternate lane and at the ends of each lane in a bowling facility.

    718.3 Draftstops in floors. Draftstops shall be installed to subdivide floor/ceiling assemblies where required by Section 708.4.3. In other than Group R occupancies, draftstops shall be installed to subdivide combustible floor/ceiling assemblies so that horizontal floor areas do not exceed 1,000 square feet (93 m [2] ).

    Exception: Buildings equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1. 718.3.1 Draftstops material. Draftstops material shall be not less than [1] / 2 -inch (12.7 mm) gypsum board, [3] / 8 -inch (9.5 mm) wood structural panel, [3] / 8 -inch (9.5 mm) particleboard, 1-inch (25-mm) nominal lumber, cement fiberboard, batts or blankets of mineral wool or glass fiber, or other approved materials adequately supported. The integrity of draftstops shall be maintained.

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

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

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

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

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

    Exceptions:

    1. Combustible materials in accordance with Section 603.

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

  • CBC § 718.4 High relevance — show source text

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

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

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

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

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

    Exceptions:

    1. Combustible materials in accordance with Section 603.

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

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

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    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.

  • CBC § 602.1.1 High relevance — show source text

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

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

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

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

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

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

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

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

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

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

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

  • CBC § 2304.11. High relevance — show source text

    The minimum dimensions for permitted materials including solid timber, glued-laminated timber, SCL and cross-laminated timber (CLT) and the details of Type IV construction shall comply with the provisions of this section and Section 2304.11. Exterior walls complying with Section 602.4.4.1 or 602.4.4.2 shall be permitted. Interior walls and partitions not less than 1-hour fire-resistance rated or heavy timber conforming with Section 2304.11.2.2 shall be permitted.

    602.4.4.1 Fire-retardant-treated wood in exterior walls. Fire-retardant-treated wood framing and sheathing complying with Section 2303.2 shall be permitted within exterior wall assemblies with a 2-hour rating or less.

    602.4.4.2 Cross-laminated timber in exterior walls. Cross-laminated timber (CLT) not less than 4 inches (102 mm) in thickness complying with Section 2303.1.4 shall be permitted within exterior wall assemblies with a 2-hour rating or less. Heavy timber structural members appurtenant to the CLT exterior wall shall meet the requirements of Table 2304.11 and be fire-resistance rated as required for the exterior wall. The exterior surface of the cross-laminated timber and heavy timber elements shall be protected by one of the following:

    1. Fire-retardant-treated wood sheathing complying with Section 2303.2 and not less than [15] / 32 inch (12 mm) thick.

    2. Gypsum board not less than [1] / 2 inch (12.7 mm) thick.

    3. A noncombustible material.

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

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

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    TYPES OF CONSTRUCTION

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

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

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

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

    SECTION 603—COMBUSTIBLE MATERIAL IN TYPES I AND II CONSTRUCTION

    **603.1 Allowable materials.

  • CBC § 717.6.2.1.2 High relevance — show source text

    717.6.2.1.2 Static systems. Static ceiling radiation dampers shall be provided with systems that are not designed to operate during a fire.

    Exceptions:

    1. Where a static ceiling radiation damper is installed at the opening of a duct, a smoke detector shall be installed inside the duct or outside the duct with sampling tubes protruding into the duct. The detector or tubes in the duct shall be within 5 feet (1524 mm) of the damper. Air outlets and inlets shall not be located between the detector or tubes and the damper. The detector shall be listed for the air velocity, temperature and humidity

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    FIRE AND SMOKE PROTECTION FEATURES

    anticipated at the point where it is installed. Other than in mechanical smoke control systems, dampers shall be closed upon fan shutdown where local smoke detectors require a minimum velocity to operate. 2. Where a static ceiling radiation damper is installed in a ceiling, the ceiling radiation damper shall be permitted to be controlled by a smoke detection system installed in the same room or area as the ceiling radiation damper. 3. A static ceiling radiation damper shall be permitted to be installed in a room where an occupant sensor is provided within the room that will shut down the system.

    717.6.3 Nonfire-resistance-rated floor assemblies. Duct systems constructed of approved materials in accordance with the California Mechanical Code that penetrate nonfire-resistance-rated floor assemblies shall be protected by any of the following methods:

    1. A shaft enclosure in accordance with Section 713.

    2. The duct connects not more than two stories, and the annular space around the penetrating duct is protected with an approved noncombustible material that resists the free passage of flame and the products of combustion.

    3. In floor assemblies composed of noncombustible materials, a shaft shall not be required where the duct connects not more than three stories, the annular space around the penetrating duct is protected with an approved noncombustible material that resists the free passage of flame and the products of combustion and a fire damper is installed at each floor line. Exception: Fire dampers are not required in ducts within individual residential dwelling units.

    717.7 Flexible ducts and air connectors. Flexible ducts and air connectors shall not pass through any fire-resistance-rated assembly. Flexible air connectors shall not pass through any wall, floor or ceiling.

    SECTION 718—CONCEALED SPACES

    718.1 General. Fireblocking and draftstops shall be installed in combustible concealed locations in accordance with this section. Fireblocking shall comply with Section 718.2. Draftstops in floor/ceiling spaces and attic spaces shall comply with Sections 718.3 and 718.4, respectively. The permitted use of combustible materials in concealed spaces of buildings of Type I or II construction shall be limited to the applications indicated in Section 718.5.

    718.2 Fireblocking. In combustible construction, fireblocking shall be installed to cut off concealed draft openings (both vertical and horizontal) and shall form an effective barrier between floors, between a top story and a roof or attic space. Fireblocking shall be installed in the locations specified in Sections 718.2.2 through 718.2.7.

  • CBC § 806.6. High relevance — show source text

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

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

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

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

    5. Trim installed in accordance with Section 806.6.

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

    7. Finish flooring installed in accordance with Section 805.

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

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

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

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

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

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

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

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

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

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

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

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    �

    TYPES OF CONSTRUCTION

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

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

  • CBC § 7-21 High relevance — show source text

    713 Shaft Enclosures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-21

    714 Penetrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-23

    715 Joints and Voids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-26

    716 Opening Protectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-27

    717 Ducts and Air Transfer Openings . . . . . . . . . . . . . . . . 7-34

    718 Concealed Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-40

    719 Fire-Resistance Requirements for Plaster . . . . . . . . 7-42

    720 Thermal- and Sound-Insulating Materials . . . . . . . . 7-42

    721 Prescriptive Fire Resistance. . . . . . . . . . . . . . . . . . . . . 7-43

    722 Calculated Fire Resistance. . . . . . . . . . . . . . . . . . . . . . 7-66

    CHAPTER 7A [SFM] MATERIALS AND CONSTRUCTION

    METHODS FOR EXTERIOR WILDFIRE EXPOSURE . . . . . . . 7A-1

    CHAPTER 8 INTERIOR FINISHES. . . . . . . . . . . . . . . . . . . . . .8-1

    801 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

    802 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

    803 Wall and Ceiling Finishes . . . . . . . . . . . . . . . . . . . . . . . . 8-3

    804 Interior Floor Finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6

    805 Combustible Materials in Types I and II Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-7

    806 Decorative Materials and Trim . . . . . . . . . . . . . . . . . . . 8-7

    807 Insulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-8

    808 Acoustical Ceiling Systems . . . . . . . . . . . . . . . . . . . . . . 8-8

    CHAPTER 9 FIRE PROTECTION AND LIFE

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

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    INTERIOR FINISHES

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

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

    SECTION 805—COMBUSTIBLE MATERIALS IN TYPES I AND II CONSTRUCTION

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

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

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

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

    SECTION 806—DECORATIVE MATERIALS AND TRIM

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

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

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

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

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

  • CBC § 5-8 High relevance — show source text

    505 Mezzanines and Equipment Platforms. . . . . . . . . . . . 5-8

    506 Building Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

    507 Unlimited Area Buildings. . . . . . . . . . . . . . . . . . . . . . . 5-13

    508 Mixed Use and Occupancy. . . . . . . . . . . . . . . . . . . . . . 5-15

    509 Incidental Uses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18

    510 Special Provisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19

    CHAPTER 6 TYPES OF CONSTRUCTION . . . . . . . . . . . . . . . 6-1

    601 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

    602 Construction Classification. . . . . . . . . . . . . . . . . . . . . . 6-3

    603 Combustible Material in Types I and II Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7

    CHAPTER 7 FIRE AND SMOKE PROTECTION FEATURES. . 7-1

    701 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

    702 Multiple-Use Fire Assemblies . . . . . . . . . . . . . . . . . . . . 7-3

    703 Fire-Resistance Ratings and Fire Tests . . . . . . . . . . . . 7-3

    704 Fire-Resistance Rating of Structural Members . . . . . 7-4

    705 Exterior Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

    706 Fire Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12

    707 Fire Barriers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14

    708 Fire Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16

    709 Smoke Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17

    710 Smoke Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-18

    711 Floor and Roof Assemblies. . . . . . . . . . . . . . . . . . . . . . 7-19

Frequently asked questions

Can I run PVC drain piping through a concealed ceiling of a Type I building?

Yes, but only if the piping is installed in accordance with the California Plumbing and Mechanical Codes and any conditions in § 603 apply; additionally, because concealed spaces in Type I construction are generally prohibited from containing combustible materials (§ 718.5), you must ensure the concealed space meets the protective options of § 602.4.4.3 (sprinklers in the space, noncombustible fill, or 5/8‑in Type X sheathing) unless another specific exception applies (§ 603.1.2) file.

Is fiberglass batt insulation allowed in a concealed space of a Type II building?

Fiberglass (non‑foam) insulation may be allowed if its flame‑spread index meets the limits in § 603.1.2 (typically ≤ 25, with certain narrowly defined exceptions) — but allowance alone does not remove the need to comply with § 718.5 and any required concealed‑space protection per § 602.4.4.3 if the space is unsprinklered file.

If the building is fully sprinklered, are combustible concealed spaces permitted?

Sprinkler protection is one of the options that allows concealed spaces to contain combustible materials under certain conditions (see § 602.4.4.3). A fully sprinklered building may relax some draftstop/fireblocking requirements, but you must still comply with the specific allowances and trade‑code installation requirements in § 603 and related sections (§ 602.4.4.3, § 603.1) file.

Does § 718.5 allow decorative wood trim in concealed spaces?

No — § 718.5 is a prohibition on combustible materials in concealed spaces with very limited exceptions. Decorative trim is normally a finish element; exposed Class A finishes are an express exception in § 718.5 only for exposed finish materials (not for concealed installations). Always confirm with § 603 and § 803 for finish classifications and specific exceptions (§ 718.5; § 803) .

Where can I find the list of acceptable fireblocking materials for concealed spaces?

Acceptable fireblocking materials (2‑in nominal lumber; 1/2‑in gypsum board; mineral wool batts; tested cellulose; mass timber; etc.) are listed in § 718.2.1 and must be used at the locations required by § 718.2.2–.7 file.

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