CBC · California Building Code

Mass timber (Type IV) protection requirements and allowable unprotected areas

For Type IV mass timber buildings the CBC requires noncombustible protection that, together with the timber, achieves the required fire‑resistance rating. Limited unprotected ceilings (up to 100% of a dwelling unit’s floor area) and walls (up to 40%) are allowed with a combined check (Equation 6‑1) and a 15‑ft minimum horizontal separation between unprotected wall portions; interior protection contributions are subject to minimum assigned times (not less than 80 minutes) and floors need a 1‑inch noncombustible layer over mass timber.

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Last reviewed: July 5, 2026

What the code requires — 2–4 sentences

For Type IV (mass timber) buildings the CBC requires mass timber elements to be protected with noncombustible materials so the combined fire‑resistance contribution of the protection and the timber meets the required rating (§ 602.4). Type IV‑A and IV‑B set minimum protection times and specify where interior faces, floors, roofs and concealed spaces must be protected, while limited unprotected areas for walls and ceilings are allowed by explicit exceptions and are subject to limits and separation distances (§ 602.4.1; § 602.4.2; § 602.4.2.2.4).

Requirements in detail

Governing rule and how protection time is determined

  • The required fire‑resistance rating for mass timber elements is determined based on the contribution of noncombustible protection, the mass timber itself, or a combination of both in accordance with § 703.2; mass timber elements in Types IV‑A, IV‑B and IV‑C must be protected with noncombustible protection applied directly to the mass timber as required in this part of § 602.4.

  • Protection time (interior protection): Noncombustible protection applied to interior faces must provide the time assigned in the referenced protection tables but not less than 80 minutes (i.e., minimum contribution = 80 minutes) for the Type IV scenarios that require protection (§ 602.4.2.2.1; § 602.4.1.2.1).

Exterior protection and coverings

  • Outside faces of exterior mass timber walls must be protected with noncombustible protection having a minimum assigned time of 40 minutes as given in the referenced table (§ 602.4.1.1; § 602.4.2.1).

Floors, roofs and concealed spaces

  • Floor assemblies must include a noncombustible material not less than 1 inch (25 mm) thick above the mass timber; finishes are permitted on top of that material (§ 602.4.1.3; § 602.4.2.3).

  • Interior roof surfaces are protected like interior mass timber faces; non‑occupiable roof spaces are treated as concealed spaces and generally must have no unprotected portions (§ 602.4.2.4; § 602.4.2.5).

Allowable unprotected areas (key decision dimensions)

The code provides specific, limited exceptions that permit unprotected portions of mass timber ceilings and walls. Decision‑relevant dimensions and values are summarized below.

Decision dimension Value / limit Code reference
Minimum interior protection contribution when required Not less than 80 minutes § 602.4.2.2.1
Minimum exterior wall noncombustible protection 40 minutes assigned time § 602.4.1.1; § 602.4.2.1
Floor assembly protection above mass timber Noncombustible layer ≥ 1 in (25 mm) § 602.4.1.3; § 602.4.2.3
Unprotected mass timber ceilings allowed (per dwelling unit / fire area) Up to 100% of floor area (Exception 1.1) § 602.4.2.2.2 Exception 1.1
Unprotected mass timber walls allowed (per dwelling unit / fire area) Up to 40% of floor area (Exception 1.2) § 602.4.2.2.2 Exception 1.2
Mixed unprotected walls + ceilings Use Equation 6‑1 to verify combined allowance § 602.4.2.2.3; Equation 6‑1
Separation between unprotected wall portions Not less than 15 ft (4,572 mm) horizontally § 602.4.2.2.4
Columns / beams not integral to walls/ceilings Can be unprotected with no aggregate area or separation restriction § 602.4.2.2.2 Exception 2

Notes on the table entries:

  • The 100% ceiling and 40% wall percentages are per dwelling unit or per fire area within a story — the code frames the exceptions on that basis (§ 602.4.2.2.2).
  • When both wall and ceiling unprotected areas exist in the same dwelling unit or fire area, the combined allowance is checked using Equation 6‑1 in § 602.4.2.2.3 (see worked example below).

How to measure and apply the separation rule

  • The 15 ft separation is measured horizontally along the floor between unprotected portions of different mass timber walls in the same dwelling unit or fire area (§ 602.4.2.2.4). This is a horizontal plan‑view measurement; corners and room geometry matter for compliance.

Exceptions & special cases

  • Columns and beams that are not integral parts of walls or ceilings may be left unprotected without aggregate area limits or separation requirements (§ 602.4.2.2.2, Exception 2). This means freestanding mass timber posts or exposed beams can be fully exposed where allowed.

  • Type IV‑C (the “unprotected” flavor of mass timber) permits mass timber elements to be unprotected under different rules; the Type IV‑C section explicitly allows unprotected mass timber elements (see § 602.4.3.2) — do not conflate IV‑B/IV‑A limits with IV‑C permissions.

  • The protection contribution used to size/assign a fire‑resistance rating must be determined in accordance with § 703.2 and the protection materials must comply with § 703.3 and the protection timing tables in Chapter 722 (Table 722.7.1(1) and related provisions). The code ties the time assigned to specific protection materials to those referenced tables (§ 602.4 and § 602.4.1.2.1).

  • Concealed spaces formed by combustible construction are generally prohibited unless they comply with the specific Type IV provisions; where allowed they must be protected per the stated sections (§ 602.4.2.5; § 602.4.1.5).

If a specific situation or product is not covered by these retrieved sections, state so and consult the code official; do not assume additional allowances beyond these sections.

Common mistakes

  • Treating the 100% and 40% allowances as building‑wide rather than per dwelling unit or per fire area within a story (the code frames the exceptions per dwelling unit/fire area) (§ 602.4.2.2.2).
  • Forgetting to apply Equation 6‑1 when both unprotected ceilings and walls are present in the same fire area or dwelling unit (§ 602.4.2.2.3).
  • Failing to check the 15 ft horizontal separation between unprotected wall portions (§ 602.4.2.2.4) — plan geometry can easily violate this spacing.
  • Overlooking the required minimum protection contribution (80 minutes) when interior faces are required to be protected (§ 602.4.2.2.1).
  • Assuming exposed beams/columns that are part of a wall/ceiling assembly are treated the same as freestanding members — the code distinguishes integral elements versus non‑integral columns/beams (§ 602.4.2.2.2).

Worked example — apartment unit applying Equation 6‑1 and separation rule

Scenario: A single dwelling unit (floor area = 1,200 sf) proposes

  • Unprotected mass timber ceiling area Utc = 600 sf
  • Unprotected mass timber wall area Utw = 200 sf Determine compliance.

Step 1 — identify allowable maxima:

  • Allowable unprotected ceiling area Uac = 100% of floor area = 1,200 sf (Exception 1.1, § 602.4.2.2.2).
  • Allowable unprotected wall area Uaw = 40% of floor area = 0.40 × 1,200 = 480 sf (Exception 1.2, § 602.4.2.2.2).

Step 2 — apply Equation 6‑1 (§ 602.4.2.2.3, Equation 6‑1) : (Utc / Uac) + (Utw / Uaw) = (600 / 1,200) + (200 / 480) = 0.50 + 0.4167 = 0.9167 ≤ 1 → Combined area passes the mixed‑area allowance.

Step 3 — check separation for unprotected wall areas (§ 602.4.2.2.4):

  • Verify that any unprotected portions of walls are at least 15 ft apart horizontally along the floor. If any two unprotected wall portions are closer than 15 ft, the wall allowance would be violated regardless of the area calculation.

Step 4 — confirm other protections:

  • Ensure floors above mass timber have the required ≥1 in noncombustible layer where applicable (§ 602.4.2.3).
  • If interior faces are otherwise required to be protected, ensure the protection provides the minimum contribution (80 minutes) or the value determined from the protection tables (§ 602.4.2.2.1).

Conclusion: In this numeric example the proposed unprotected areas comply with the mixed‑area equation, provided the 15 ft separation test and the other protection requirements are met.

Related provisions (CBC sections you should review)

  • § 602.4 — Type IV general statement and protection requirement references.
  • § 602.4.1 — Type IV‑A protection requirements (exterior/interior/floors/roofs/shafts).
  • § 602.4.2 — Type IV‑B protection requirements including the interior protection exceptions and the mixed‑area rule.
  • § 602.4.2.2.4 — Separation distance between unprotected mass timber elements (15 ft).
  • § 602.4.3 — Type IV‑C notes (mass timber elements permitted to be unprotected) — compare if considering IV‑C.
  • § 703.2 — Determination of required fire‑resistance rating (used to evaluate combined protection + timber).
  • § 703.3 — Materials permitted for interior protection (when interior faces are required to be protected).
  • Chapter 722 / Table 722.7.1(1) and § 722.7 references — assignment of protection times and acceptable protection systems (minimums referenced in §§ above).
  • § 718 and §§ 713 — Concealed spaces and shafts requirements (where cited in Type IV sections).

If you need code‑level text for any of these related sections or a plan‑check checklist that walks through everything an applicant must submit to demonstrate compliance, I can produce that next.

Code references

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

  • CBC § 703.2. High relevance — show source text

    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.

    In buildings of Type IV-A, IV-B, and IV-C construction with an occupied floor located more than 75 feet (22 860 mm) above the lowest level of fire department vehicle access, up to and including 12 stories or 180 feet (54 864 mm) above grade plane, mass timber interior exit and elevator hoistway enclosures shall be protected in accordance with Section 602.4.1.2. In buildings greater than 12 stories or 180 feet (54 864 mm) above grade plane, interior exit and elevator hoistway enclosures shall be constructed of noncombustible materials.

    602.4.1 Type IV-A. Building elements in Type IV-A construction shall be protected in accordance with Sections 602.4.1.1 through 602.4.1.6. The required fire-resistance rating of noncombustible elements and protected mass timber elements shall be determined in accordance with Section 703.2.

    602.4.1.1 Exterior protection. The outside face of exterior walls of mass timber construction shall be protected with noncombustible protection with a minimum assigned time of 40 minutes, as specified in Table 722.7.1(1). Components of the exterior wall covering shall be of noncombustible material except water-resistive barriers having a peak heat release rate of less than 150kW/m [2], a total heat release of less than 20 MJ/m [2] and an effective heat of combustion of less than 18MJ/kg as determined in accordance with ASTM E1354 and having a flame spread index of 25 or less and a smoke-developed index of 450 or less as

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  • CBC § 6-1 High relevance — show source text

    Equation 6-1 ( U tc / U ac ) + ( U tw / U aw ) ≤ 1

    where:

    U tc = Total unprotected mass timber ceiling areas. U ac = Allowable unprotected mass timber ceiling area conforming to Exception 1.1 of Section 602.4.2.2.2.

    U tw = Total unprotected mass timber wall areas.

    U aw = Allowable unprotected mass timber wall area conforming to Exception 1.2 of Section 602.4.2.2.2.

    602.4.2.2.4 Separation distance between unprotected mass timber elements. In each dwelling unit or fire area, unprotected portions of mass timber walls shall be not less than 15 feet (4572 mm) from unprotected portions of other walls measured horizontally along the floor.

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    602.4.2.3 Floors. The floor assembly shall contain a noncombustible material not less than 1 inch (25 mm) in thickness above the mass timber. Floor finishes in accordance with Section 804 shall be permitted on top of the noncombustible material. Except where unprotected mass timber ceilings are permitted in Section 602.4.2.2.2, the underside of floor assemblies shall be protected in accordance with Section 602.4.1.2.

    602.4.2.4 Roofs. The interior surfaces of roof assemblies shall be protected in accordance with Section 602.4.2.2 except, in nonoccupiable spaces, they shall be treated as a concealed space with no portion left unprotected. Roof coverings in accordance with Chapter 15 shall be permitted on the outside surface of the roof assembly.

    602.4.2.5 Concealed spaces. Concealed spaces shall not contain combustibles other than electrical, mechanical, fire protection, or plumbing materials and equipment permitted in plenums in accordance with the California Mechanical Code, and shall comply with all applicable provisions of Section 718. Combustible construction forming concealed spaces shall be protected in accordance with Section 602.4.1.2.

    602.4.2.6 Shafts. Shafts shall be permitted in accordance with Sections 713 and 718. Both the shaft side and room side of mass timber elements shall be protected in accordance with Section 602.4.1.2.

    602.4.3 Type IV-C. Building elements in Type IV-C construction shall be protected in accordance with Sections 602.4.3.1 through 602.4.3.6. The required fire-resistance rating of building elements shall be determined in accordance with Section 703.2.

    602.4.3.1 Exterior protection. The exterior side of walls of combustible construction shall be protected with noncombustible protection with a minimum assigned time of 40 minutes, as determined in Table 722.7.1(1).

  • CBC § 602.4.2.2.1 High relevance — show source text

    602.4.2.2.1 Protection time. Noncombustible protection shall contribute a time equal to or greater than times assigned in Table 722.7.1(1), but not less than 80 minutes. The use of materials and their respective protection contributions specified in Table 722.7.1(2) shall be permitted to be used for compliance with Section 722.7.1.

    602.4.2.2.2 Protected area. Interior faces of mass timber elements, including the inside face of exterior mass timber walls and mass timber roofs, shall be protected in accordance with Section 602.4.2.2.1.

    Exceptions: Unprotected portions of mass timber ceilings and walls complying with Section 602.4.2.2.4 and the following:

    1. Unprotected portions of mass timber ceilings and walls complying with one of the following: 1.1. Unprotected portions of mass timber ceilings, including attached beams, limited to an area less than or equal to 100 percent of the floor area in any dwelling unit within a story or fire area within a story. 1.2. Unprotected portions of mass timber walls, including attached columns, limited to an area less than or equal to 40 percent of the floor area in any dwelling unit within a story or fire area within a story. 1.3. Unprotected portions of both walls and ceilings of mass timber, including attached columns and beams, in any dwelling unit or fire area and in compliance with Section 602.4.2.2.3.
    2. Mass timber columns and beams that are not an integral portion of walls or ceilings, respectively, without restriction of either aggregate area or separation from one another.

    602.4.2.2.3 Mixed unprotected areas. In each dwelling unit or fire area, where both portions of ceilings and portions of walls are unprotected, the total allowable unprotected area shall be determined in accordance with Equation 6-1.

    Equation 6-1 ( U tc / U ac ) + ( U tw / U aw ) ≤ 1

    where:

    U tc = Total unprotected mass timber ceiling areas. U ac = Allowable unprotected mass timber ceiling area conforming to Exception 1.1 of Section 602.4.2.2.2.

    U tw = Total unprotected mass timber wall areas.

    U aw = Allowable unprotected mass timber wall area conforming to Exception 1.2 of Section 602.4.2.2.2.

    602.4.2.2.4 Separation distance between unprotected mass timber elements. In each dwelling unit or fire area, unprotected portions of mass timber walls shall be not less than 15 feet (4572 mm) from unprotected portions of other walls measured horizontally along the floor.

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    602.4.2.3 Floors. The floor assembly shall contain a noncombustible material not less than 1 inch (25 mm) in thickness above the mass timber. Floor finishes in accordance with Section 804 shall be permitted on top of the noncombustible material. Except where unprotected mass timber ceilings are permitted in Section 602.4.2.2.2, the underside of floor assemblies shall be protected in accordance with Section 602.4.1.2.

  • CBC § 602.4.1.6 High relevance — show source text

    602.4.1.6 Shafts. Shafts shall be permitted in accordance with Sections 713 and 718. Both the shaft side and room side of mass timber elements shall be protected in accordance with Section 602.4.1.2.

    602.4.2 Type IV-B. Building elements in Type IV-B construction shall be protected in accordance with Sections 602.4.2.1 through 602.4.2.6. The required fire-resistance rating of noncombustible elements or mass timber elements shall be determined in accordance with Section 703.2.

    602.4.2.1 Exterior protection. The outside face of exterior walls of mass timber construction shall be protected with noncombustible protection with a minimum assigned time of 40 minutes, as specified in Table 722.7.1(1). Components of the exterior wall covering shall be of noncombustible material except water-resistive barriers having a peak heat release rate of less than 150kW/m [2], a total heat release of less than 20 MJ/m [2] and an effective heat of combustion of less than 18MJ/kg as determined in accordance with ASTM E1354, and having a flame spread index of 25 or less and a smoke-developed index of 450 or less as determined in accordance with ASTM E84 or UL 723. The ASTM E1354 test shall be conducted on specimens at the thickness intended for use, in the horizontal orientation and at an incident radiant heat flux of 50 kW/m [2] .

    602.4.2.2 Interior protection. Interior faces of all mass timber elements, including the inside face of exterior mass timber walls and mass timber roofs, shall be protected, as required by this section, with materials complying with Section 703.3.

    602.4.2.2.1 Protection time. Noncombustible protection shall contribute a time equal to or greater than times assigned in Table 722.7.1(1), but not less than 80 minutes. The use of materials and their respective protection contributions specified in Table 722.7.1(2) shall be permitted to be used for compliance with Section 722.7.1.

    602.4.2.2.2 Protected area. Interior faces of mass timber elements, including the inside face of exterior mass timber walls and mass timber roofs, shall be protected in accordance with Section 602.4.2.2.1.

    Exceptions: Unprotected portions of mass timber ceilings and walls complying with Section 602.4.2.2.4 and the following:

    1. Unprotected portions of mass timber ceilings and walls complying with one of the following: 1.1. Unprotected portions of mass timber ceilings, including attached beams, limited to an area less than or equal to 100 percent of the floor area in any dwelling unit within a story or fire area within a story. 1.2. Unprotected portions of mass timber walls, including attached columns, limited to an area less than or equal to 40 percent of the floor area in any dwelling unit within a story or fire area within a story. 1.3. Unprotected portions of both walls and ceilings of mass timber, including attached columns and beams, in any dwelling unit or fire area and in compliance with Section 602.4.2.2.3.
    2. Mass timber columns and beams that are not an integral portion of walls or ceilings, respectively, without restriction of either aggregate area or separation from one another.
  • 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 § 602.4.1.2.1 High relevance — show source text

    602.4.1.2.1 Protection time. Noncombustible protection shall contribute a time equal to or greater than times assigned in Table 722.7.1(1), but not less than 80 minutes. The use of materials and their respective protection contributions specified in Table 722.7.1(2) shall be permitted to be used for compliance with Section 722.7.1.

    602.4.1.3 Floors. The floor assembly shall contain a noncombustible material not less than 1 inch (25 mm) in thickness above the mass timber. Floor finishes in accordance with Section 804 shall be permitted on top of the noncombustible material. The underside of floor assemblies shall be protected in accordance with Section 602.4.1.2.

    602.4.1.4 Roofs. The interior surfaces of roof assemblies shall be protected in accordance with Section 602.4.1.2. Roof coverings in accordance with Chapter 15 shall be permitted on the outside surface of the roof assembly.

    602.4.1.5 Concealed spaces. Concealed spaces shall not contain combustibles other than electrical, mechanical, fire protection, or plumbing materials and equipment permitted in plenums in accordance with the California Mechanical Code, and shall comply with all applicable provisions of Section 718. Combustible construction forming concealed spaces shall be protected in accordance with Section 602.4.1.2.

    602.4.1.6 Shafts. Shafts shall be permitted in accordance with Sections 713 and 718. Both the shaft side and room side of mass timber elements shall be protected in accordance with Section 602.4.1.2.

    602.4.2 Type IV-B. Building elements in Type IV-B construction shall be protected in accordance with Sections 602.4.2.1 through 602.4.2.6. The required fire-resistance rating of noncombustible elements or mass timber elements shall be determined in accordance with Section 703.2.

    602.4.2.1 Exterior protection. The outside face of exterior walls of mass timber construction shall be protected with noncombustible protection with a minimum assigned time of 40 minutes, as specified in Table 722.7.1(1). Components of the exterior wall covering shall be of noncombustible material except water-resistive barriers having a peak heat release rate of less than 150kW/m [2], a total heat release of less than 20 MJ/m [2] and an effective heat of combustion of less than 18MJ/kg as determined in accordance with ASTM E1354, and having a flame spread index of 25 or less and a smoke-developed index of 450 or less as determined in accordance with ASTM E84 or UL 723. The ASTM E1354 test shall be conducted on specimens at the thickness intended for use, in the horizontal orientation and at an incident radiant heat flux of 50 kW/m [2] .

    602.4.2.2 Interior protection. Interior faces of all mass timber elements, including the inside face of exterior mass timber walls and mass timber roofs, shall be protected, as required by this section, with materials complying with Section 703.3.

  • CBC § 4.1 High relevance — show source text

    1705 A .4.1 Glass unit masonry and masonry veneer in Risk Category II, III or IV. Special inspections and tests for glass unit masonry or masonry veneer designed in accordance with Section 2110 A or Chapter 14, respectively, where they are part of a structure classified as Risk Category II, III or IV shall be performed in accordance with TMS 602 Tables 3 and 4, Level 2.

    1705A.4.1.1 TMS 602 Section 1.6 Quality Assurance. Replace footnote (d) in TMS 602 Table 4 as follows:

    (d) Periodic special inspection is required for all veneer.

    1705 A .4.2 Vertical masonry foundation elements. Special inspections and tests of vertical masonry foundation elements shall be performed in accordance with Section 1705 A .4.

    1705 A .5 Wood construction. Special inspections of prefabricated wood structural elements and assemblies shall be in accordance with Section 1704 A .2.5 except as modified in this section . Special inspections of site-built assemblies shall be in accordance with this section.

    1705 A .5.1 High-load diaphragms. High-load diaphragms designed in accordance with Section 2306.2 or 2307.1 shall be installed with special inspections as indicated in Section 1704 A .2. The special inspector shall inspect the wood structural panel sheathing to ascertain whether it is of the grade and thickness shown on the approved construction documents. Additionally, the special inspector must verify the nominal size of framing members at adjoining panel edges, the nail or staple diameter and length, the number of fastener lines and that the spacing between fasteners in each line and at edge margins agrees with the approved construction documents.

    1705 A .5.2 Metal-plate-connected wood trusses spanning 60 feet or greater. Where a truss clear span is 60 feet (18 288 mm) or greater, the special inspector shall verify that the temporary installation restraint/bracing and the permanent individual truss member restraint/bracing are installed in accordance with the approved truss submittal package.

    1705 A .5.3 Mass timber construction. Special inspections of mass timber elements in Types IV-A, IV-B and IV-C construction shall be in accordance with Table 1705 A .5.3.

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    SPECIAL INSPECTIONS AND TESTS

    TABLE 1705A.5.3—REQUIRED SPECIAL INSPECTIONS OF MASS TIMBER CONSTRUCTION Col2 Col3 Col4
    TYPE TYPE CONTINUOUS
    SPECIAL
    INSPECTION    		 PERIODIC
    SPECIAL
    INSPECTION
    1. Inspection of anchorage and connections of mass timber construction to timber deep foundation
    systems.    		 — X
    2. Inspect erection of mass timber construction. — X
    3. Inspection of connections where installation methods are required to meet design loads.
    _3.1.
  • CBC § 602.4.1 High relevance — show source text

    602.4.1 Type IV-A. Building elements in Type IV-A construction shall be protected in accordance with Sections 602.4.1.1 through 602.4.1.6. The required fire-resistance rating of noncombustible elements and protected mass timber elements shall be determined in accordance with Section 703.2.

    602.4.1.1 Exterior protection. The outside face of exterior walls of mass timber construction shall be protected with noncombustible protection with a minimum assigned time of 40 minutes, as specified in Table 722.7.1(1). Components of the exterior wall covering shall be of noncombustible material except water-resistive barriers having a peak heat release rate of less than 150kW/m [2], a total heat release of less than 20 MJ/m [2] and an effective heat of combustion of less than 18MJ/kg as determined in accordance with ASTM E1354 and having a flame spread index of 25 or less and a smoke-developed index of 450 or less as

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    determined in accordance with ASTM E84 or UL 723. The ASTM E1354 test shall be conducted on specimens at the thickness intended for use, in the horizontal orientation and at an incident radiant heat flux of 50 kW/m [2] .

    602.4.1.2 Interior protection. Interior faces of all mass timber elements, including the inside faces of exterior mass timber walls and mass timber roofs, shall be protected with materials complying with Section 703.3.

    602.4.1.2.1 Protection time. Noncombustible protection shall contribute a time equal to or greater than times assigned in Table 722.7.1(1), but not less than 80 minutes. The use of materials and their respective protection contributions specified in Table 722.7.1(2) shall be permitted to be used for compliance with Section 722.7.1.

    602.4.1.3 Floors. The floor assembly shall contain a noncombustible material not less than 1 inch (25 mm) in thickness above the mass timber. Floor finishes in accordance with Section 804 shall be permitted on top of the noncombustible material. The underside of floor assemblies shall be protected in accordance with Section 602.4.1.2.

    602.4.1.4 Roofs. The interior surfaces of roof assemblies shall be protected in accordance with Section 602.4.1.2. Roof coverings in accordance with Chapter 15 shall be permitted on the outside surface of the roof assembly.

    602.4.1.5 Concealed spaces. Concealed spaces shall not contain combustibles other than electrical, mechanical, fire protection, or plumbing materials and equipment permitted in plenums in accordance with the California Mechanical Code, and shall comply with all applicable provisions of Section 718. Combustible construction forming concealed spaces shall be protected in accordance with Section 602.4.1.2.

    602.4.1.6 Shafts. Shafts shall be permitted in accordance with Sections 713 and 718. Both the shaft side and room side of mass timber elements shall be protected in accordance with Section 602.4.1.2.

  • CBC § 602.4.3.2 High relevance — show source text

    The ASTM E1354 test shall be conducted on specimens at the thickness intended for use, in the horizontal orientation and at an incident radiant heat flux of 50 kW/m [2] .

    602.4.3.2 Interior protection. Mass timber elements are permitted to be unprotected.

    602.4.3.3 Floors. Floor finishes in accordance with Section 804 shall be permitted on top of the floor construction.

    602.4.3.4 Roof coverings. Roof coverings in accordance with Chapter 15 shall be permitted on the outside surface of the roof assembly.

    602.4.3.5 Concealed spaces. Concealed spaces shall not contain combustibles other than electrical, mechanical, fire protection, or plumbing materials and equipment permitted in plenums in accordance with the California Mechanical Code, and shall comply with all applicable provisions of Section 718. Combustible construction forming concealed spaces shall be protected with noncombustible protection with a minimum assigned time of 40 minutes, as specified in Table 722.7.1(1).

    602.4.3.6 Shafts. Shafts shall be permitted in accordance with Sections 713 and 718. Shafts and elevator hoistway and interior exit stairway enclosures shall be protected with noncombustible protection with a minimum assigned time of 40 minutes, as specified in Table 722.7.1(1), on both the inside of the shaft and the outside of the shaft.

    602.4.4 Type IV-HT. Type IV-HT (Heavy Timber) construction is that type of construction in which the exterior walls are of noncombustible materials and the interior building elements are of solid wood, laminated heavy timber or structural composite lumber (SCL), without concealed spaces or with concealed spaces complying with Section 602.4.4.3. 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.

  • CBC § 0.42 High relevance — show source text

    Spacing of fasteners not included in this table shall be based on Table R602.3(2).
    f. For wood structural panel roof sheathing attached to gable end roof framing and to intermediate supports within 48 inches of roof edges and ridges, nails shall be spaced at 4
    inches on center where the ultimate design wind speed is greater than 130 mph in Exposure B or greater than 110 mph in Exposure C. Fastener spacing applies where roof
    framing specific gravity is 0.42 or larger. Where roof framing specific gravity is greater than or equal to 0.35 but less than 0.42 in accordance with AWC NDS, fastening of roof
    sheathing shall be with RSRS-03 (21/2″ × 0.131″ × 0.281″ head) nails.
    g. Gypsum sheathing shall conform to ASTM C1396 and shall be installed in accordance with ASTM C1280 or GA 253 . Fiberboard sheathing shall conform to ASTM C208.
    h. Spacing of fasteners on floor sheathing panel edges applies to panel edges supported by framing members and required blocking and at floor perimeters only. Spacing of fasteners
    on roof sheathing panel edges applies to panel edges supported by framing members and required blocking. Blocking of roof or floor sheathing panel edges perpendicular to the
    framing members need not be provided except as required by other provisions of this code. Floor perimeter shall be supported by framing members or solid blocking.
    i. Where a rafter is fastened to an adjacent parallel ceiling joist in accordance with this schedule, provide two toe nails on one side of the rafter and toe nails from the ceiling joist
    to top plate in accordance with this schedule. The toe nail on the opposite side of the rafter shall not be required.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s; 1 ksi = 6.895 MPa.
    a. Nails are smooth-common, box or deformed shanks except where otherwise stated. Nails used for framing and sheathing connections are carbon steel and shall have mini-
    mum average bending yield strengths as shown: 80 ksi for shank diameter of 0.192 inch (20d common nail), 90 ksi for shank diameters larger than 0.142 inch but not larger than
    0.177 inch, and 100 ksi for shank diameters of 0.142 inch or less. Connections using nails and staples of other materials, such as stainless steel, shall be designed by accepted
    engineering practice or approved under Section R104.2.2.
    b. RSRS-01 is a Roof Sheathing Ring Shank nail meeting the specifications in ASTM F1667.
    c. Nails shall be spaced at not more than 6 inches on center at all supports where spans are 48 inches or greater.
    d. Four-foot by 8-foot or 4-foot by 9-foot panels shall be applied vertically.
    e. Spacing of fasteners not included in this table shall be based on Table R602.3(2).
    f. For wood structural panel roof sheathing attached to gable end roof framing and to intermediate supports within 48 inches of roof edges and ridges, nails shall be spaced at 4
    inches on center where the ultimate design wind speed is greater than 130 mph in Exposure B or greater than 110 mph in Exposure C. Fastener spacing applies where roof
    framing specific gravity is 0.42 or larger.

  • CBC § 2104A.1.3.10.2 High relevance — show source text

    2104A.1.3.10.2 TMS 402, Section 5.1.3.2 Composite action. Replace TMS 402, Section 5.1.3.2.1 by the following:

    5.1.3.2.1 Multiwythe masonry designed for composite action shall have wythes connected by collar joints and wall ties.

    2104A.1.3.10.3 TMS 602, Article 3.3 B.4 Placing mortar and units – Solid units. Add the following to TMS 602, Article 3.3 B.4: d. Toothing of masonry walls is prohibited. Racking is to be held to a minimum.

    2104A.1.3.10.4 TMS 602, Article 3.4 C.2 Wall ties. Replace TMS 602, Article 3.4 C.2 as follows: 2. The two wythes shall be bonded together with wall ties. Ties shall not be less than No. 9 (W1.7) wire in the form of rect- angles 4 inches (102 mm) wide and 2 inches (50.8 mm) in length less than the overall wall thickness. Kinks, water drips or deformations shall not be permitted in the ties. One wythe of the wall shall be built up not more than 16 inches (406 mm) ahead of the other wythe. Ties shall be laid not to exceed 24 inches (610 mm) on center horizontally and 16 inches (406 mm) on center vertically for running bond, and not more than 24 inches (610 mm) on center horizontally and 12 inches (305 mm) on center vertically for other than running bond.

    2104A.1.3.10.5 TMS 602, Article 3.5 B Confinement. Add the following to TMS 602, Article 3.5 B: 1. Construct vertical grout barriers or dams of solid masonry across the grout space the entire height of the wall to control horizontal grout flow. Space grout barriers not more than 30 feet (9.14 m) apart.

    2104A.1.3.11 Reinforced hollow unit masonry.

    2104A.1.3.11.1 TMS 602, Article 2.3 A & 2.3 B Masonry unit materials. Add the following to TMS 602, Articles 2.3 A and 2.3 B: 1. In reinforced hollow unit masonry, place horizontal reinforcement in bond beam units. The depth of the bond beam channel below the top of the unit shall be 1 [1] / 2 inches (38.1 mm) minimum and the width shall be 3 inches (76.2 mm) minimum.

  • CBC § 1.1.6 High relevance — show source text

    1.1.6 Nonbuilding standards, orders and regulations. Requirements contained in the California Building Code, or in any other refer- enced standard, code or document, which are not building standards as defined in Health and Safety Code Section 18909, shall not be construed as part of the provisions of this code. For nonbuilding standards, orders and regulations, see other titles of the California Code of Regulations.

    1.1.7 Order of precedence and use.

    1.1.7.1 Differences. In the event of any differences between these building standards and the standard reference documents, the text of these building standards shall govern.

    1.1.7.2 Specific provisions. Where a specific provision varies from a general provision, the specific provision shall apply.

    1-4 2025 CALIFORNIA BUILDING CODE

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

    ADMINISTRATION

    1.1.7.3 Conflicts. When the requirements of this code conflict with the requirements of any other part of the California Building Standards Code, Title 24, the most restrictive requirements shall prevail.

    1.1.7.3.1 Detached one- and two-family dwellings. Detached one- and two-family dwellings, lodging houses, live/work units, townhouses not more than three stories above grade plane in height with a separate means of egress, and their accessory struc- tures, may be designed and constructed in accordance with this code or the California Residential Code, but not both, unless the proposed structure(s) or element(s) exceed the design limitations established in the California Residential Code, and the code user is specifically directed by the California Residential Code to use this code.

    1.1.8 City, county, or city and county amendments, additions or deletions. The provisions of this code do not limit the authority of city, county, or city and county governments to establish more restrictive and reasonably necessary differences to the provisions contained in this code pursuant to complying with Section 1.1.8.1. The effective date of amendments, additions or deletions to this code by a city, county, or city and county filed pursuant to Section 1.1.8.1 shall be the date filed. However, in no case shall the amendments, additions or deletions to this code be effective any sooner than the effective date of this code.

    Local modifications shall comply with Health and Safety Code Section 18941.5 for Building Standards Law, Health and Safety Code Section 17958 for State Housing Law or Health and Safety Code Section 13869.7 for Fire Protection Districts.

    1.1.8.1 Findings and filings. 1. The city, county, or city and county shall make express findings for each amendment, addition or deletion based upon climatic, topographical or geological conditions. Exception: Hazardous building ordinances and programs mitigating unreinforced masonry buildings. 2. The city, county, or city and county shall file the amendments, additions or deletions expressly marked and identified as to the applicable findings. Cities, counties, cities and counties, and fire departments shall file the amendments, additions or deletions, and the findings with the California Building Standards Commission at 2525 Natomas Park Drive, Suite 130, Sacramento, CA 95833.

Frequently asked questions

Do the 100% ceiling and 40% wall allowances apply to an entire building or per apartment?

They apply per dwelling unit or per fire area within a story — the exceptions in § 602.4.2.2.2 are framed on that basis, not building‑wide.

How do I handle a room that has both unprotected exposed ceilings and exposed walls?

Use Equation 6‑1 in § 602.4.2.2.3 to combine the ceiling and wall unprotected areas and verify the sum is ≤ 1; see the worked example above.

Is there a required horizontal separation between unprotected wall openings?

Yes — unprotected portions of mass timber walls in the same dwelling unit or fire area must be at least 15 ft (4,572 mm) apart measured horizontally along the floor (§ 602.4.2.2.4).

Can exposed beams or columns be left unprotected?

Yes — mass timber columns and beams that are not integral parts of walls or ceilings may be left unprotected without aggregate area or separation restrictions (Exception 2 to § 602.4.2.2.2).

What is the minimum protection time if interior faces must be protected?

When interior noncombustible protection is required it must contribute the time assigned in the protection tables but not less than 80 minutes for the referenced Type IV requirements (§ 602.4.2.2.1).

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California Building Code