CBC · California Building Code

What are the durability requirements for concrete (exposure, cover, minimum strength)?

The California Building Code requires structural concrete to meet ACI 318 durability provisions and requires the design professional to assign exposure classes for nonstructural concrete; CBC §1904.2 sets minimum compressive strengths for nonstructural classes (2,500–3,500 psi) and mandates air entrainment where freeze–thaw exposure applies, while an R‑2/R‑3 exception requires certain exterior/basement vertical surfaces to have at least 3,000 psi. Consult ACI 318 for the exact cover, air‑content, and other exposure‑specific details referenced by CBC §1904.

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Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

The California Building Code (CBC) directs that structural concrete meet the durability provisions of ACI 318 (CBC §1904.1). For nonstructural concrete the registered design professional must assign a freeze–thaw exposure class and use the CBC minimum compressive strengths for those classes; nonstructural concrete exposed to freezing must be air-entrained (CBC §1904.2). The CBC also establishes minimum f′c limits for many applications by reference to ACI 318 and CBC tables (see CBC §19.2.1.1 for f′c limits and CBC §1904.1–§1904.2 for the durability rules) .

Requirements in detail

1) Structural concrete: where to look and who decides

  • Rule: Structural concrete must “conform to the durability requirements of ACI 318.” The CBC does not restate ACI 318’s detailed exposure/cover tables; it incorporates them by reference (CBC §1904.1) .
  • Practical effect: cover depths, required air content for freeze–thaw, required cement type, allowable admixtures, and many exposure-based choices are governed by ACI 318 as adopted by the CBC. If you need the specific cover or air‑content numbers, consult ACI 318 (as adopted) or the building official.

2) Nonstructural concrete — exposure classes, minimum f′c, air entrainment

  • The registered design professional must assign the freeze–thaw exposure class for nonstructural concrete per ACI 318; CBC then requires minimum 28‑day compressive strengths and air entrainment for nonstructural concrete (CBC §1904.2) .

Decision‑relevant dimensions/values

Decision item Value / requirement Code reference
Structural concrete durability standard Conform to ACI 318 (durability provisions govern cover, air, materials, etc.) §1904.1
Exception — R‑2 and R‑3 small buildings For Group R‑2 and R‑3, ≤ 3 stories above grade, concrete in basement walls, foundation walls, exterior walls and other vertical surfaces exposed to the weather shall have f′c ≥ 3,000 psi (20.7 MPa) §1904.1 (exception)
Nonstructural — exposure class F0 (no freeze–thaw) Minimum f′c = 2,500 psi (17.2 MPa); (no air‑entrainment requirement stated here) §1904.2
Nonstructural — exposure class F1 Minimum f′c = 3,000 psi (20.7 MPa); air‑entrained per ACI 318 §1904.2
Nonstructural — exposure class F2 or F3 Minimum f′c = 3,500 psi (24.1 MPa); air‑entrained per ACI 318 §1904.2
CBC general limits for f′c (many structural applications) General minimum f′c = 3,000 psi; some specialized elements (piles, shotcrete, special walls) have higher minima — see CBC Table 19.2.1.1 §19.2.1.1 (Table 19.2.1.1)

Notes:

  • The CBC text places the detailed mapping of exposure conditions → cover depth → air content in ACI 318; the CBC sections above require conformity to ACI 318 rather than listing those values in full (CBC §1904.1 and §1904.2) .
  • Table 19.2.1.1 in the CBC sets other minimum f′c limits used when designing members (for example, “General” = 3000 psi and shotcrete = 4000 psi) and is used together with the durability requirements (CBC §19.2.1.1) .

3) Cover (concrete cover to reinforcement)

  • What the CBC says: the CBC requires structural concrete to meet ACI 318 durability rules, and those ACI provisions establish required minimum concrete cover by exposure condition and member type (CBC §1904.1) .
  • What the CBC text here does not provide: the §1904 text itself does not reproduce the ACI cover tables (i.e., specific mm/inch cover by exposure and bar condition). Therefore you must consult the adopted ACI 318 durability tables or the enforcement agency’s requirements for the exact cover dimension for a given exposure.

Exceptions & special cases

  • R‑2 and R‑3 small residential exception: For Group R‑2 and R‑3 occupancies not more than three stories above grade plane, concrete in basement walls, foundation walls, exterior walls and other vertical surfaces exposed to the weather must have f′c ≥ 3,000 psi (CBC §1904.1 exception) .
  • Nonstructural items: the registered design professional must assign the exposure class (F0–F3 per ACI 318) — the CBC enforces the minimum f′c for each class and requires air entrainment for the freeze–thaw classes (CBC §1904.2) .
  • Other CBC minima: Table 19.2.1.1 (CBC §19.2.1.1) provides minimum f′c limits for many structural situations (special moment frames, shotcrete, piles, etc.) and interacts with the durability requirements when selecting f′c .

Common mistakes

  • Assuming CBC §1904 itself lists cover depths: CBC §1904 incorporates ACI 318 for those details; CBC §1904 does not reprint the ACI cover tables, so designers who quote cover values must cite ACI 318 or the enforcement agency’s adoption, not §1904 alone .
  • Forgetting to assign an exposure class: CBC requires the registered design professional to assign the freeze–thaw exposure class for nonstructural concrete; failing to do so leads to incorrect f′c and missing air‑entrainment requirements (CBC §1904.2) .
  • Applying nonstructural minimums to structural members: structural concrete is governed by ACI 318 (as adopted) and CBC minima in Table 19.2.1.1; do not substitute nonstructural F‑class minima for required structural f′c values (compare CBC §1904.1 and §19.2.1.1) .
  • Omitting air entrainment where required: CBC explicitly requires nonstructural concrete to be air entrained in accordance with ACI 318 when assigned an exposure class per §1904.2 .

Worked example — applying the rules with numbers

Scenario: A registered design professional is specifying a 4‑inch exterior concrete stair landing (nonstructural element) in northern California that is expected to be exposed to freezing and deicing salts.

Step 1 — assign exposure class:

  • Because the landing will experience freeze–thaw and possible deicing chemicals, the design professional assigns exposure Class F2 (or F3 if heavy chemical exposure is expected) per ACI 318; CBC §1904.2 requires the design professional to make that assignment .

Step 2 — pick minimum f′c from CBC §1904.2:

  • For F2 (or F3) CBC §1904.2 requires minimum f′c = 3,500 psi (24.1 MPa) and requires air entrainment in accordance with ACI 318 .

Step 3 — ensure air content and cover per ACI 318:

  • CBC §1904.2 requires air entrainment; the specific percent air and minimum cover come from ACI 318’s durability tables (consult ACI 318 for the exact air percentage and cover required for F2/F3). CBC §1904.1 and §1904.2 together point you to ACI 318 for the detailed values .

Step 4 — cross‑check other CBC minima:

  • Confirm the selected f′c (3,500 psi) also meets any CBC Table 19.2.1.1 minima applicable to the element type; if the stair landing were a shotcrete element, CBC Table 19.2.1.1 imposes a 4,000 psi minimum for shotcrete (CBC §19.2.1.1) .

Summary for this example: specify f′c ≥ 3,500 psi, specify air entrainment per ACI 318, and choose cover per ACI 318 for the exposure class F2/F3; verify no other CBC table raises the f′c requirement for that element.

Related provisions — other CBC sections to consult

  • CBC §1904 — Durability requirements (general)
  • CBC §1904.1 — Structural concrete (conform to ACI 318; R‑2/R‑3 exception)
  • CBC §1904.2 — Nonstructural concrete: exposure classes, minimum f′c values, air entrainment requirement
  • CBC §19.2.1.1 — Limits and minimums for f′c (Table 19.2.1.1) that interact with durability rules
  • CBC §1903 / §1903.1 — Specifications for materials and tests; materials must comply with standards listed in ACI 318 (useful when specifying cement, admixtures, tests)
  • CBC Chapter 19A (where applicable) — California-specific modifications to ACI text; see 1904A for the A‑chapter counterpart

Code references

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

  • CBC § 1903.5 High relevance — show source text

    1903.5 Welding of reinforcing bars - [OSHPD 1R, 2 & 5] Modify ACI 318 Section 26.6.4.1(b) by adding the following:

    Subject to prior approval of the enforcing agency, longitudinal holding wires conforming to ASTM A1064, of maximum wire size W5, that are machine resistance welded to stirrup/tie cage (or spiral assemblies) consisting of low alloy steel reinforcing conforming to ASTM A706 are permitted when performed under continuous competent control in a fabrication shop. Tack welding of primary rein- forcing bars together or to stirrups/ties is not permitted. Holding wire weld locations shall not occur on any longitudinal or primary reinforcing nor on any portion of a reinforcing bar that is or will be bent in accordance with ACI 318 Section 25.3 for the extents speci- fied in AWS D1.4 Section 4.2.6.

    Quality control tests shall be performed on shop welded specimens by the fabricator. Reinforcing steel specimens containing the holding wire shall be tested for yield and tensile strength at the frequency required by Section 1910.2. Test reports shall be available on request to the approved agency, design professional and enforcement agency.

    SECTION 1904—DURABILITY REQUIREMENTS

    1904.1 Structural concrete. Structural concrete shall conform to the durability requirements of ACI 318.

    Exception: For Group R-2 and R-3 occupancies not more than three stories above grade plane, the specified compressive strength, f´ c, for concrete in basement walls, foundation walls, exterior walls and other vertical surfaces exposed to the weather shall be not less than 3,000 psi (20.7 MPa).

    1904.2 Nonstructural concrete. The registered design professional shall assign nonstructural concrete a freeze-thaw exposure class, as defined in ACI 318, based on the anticipated exposure of nonstructural concrete. Nonstructural concrete shall have a minimum specified compressive strength, f´ c, of 2,500 psi (17.2 MPa) for Class F0; 3,000 psi (20.7 MPa) for Class F1; and 3,500 psi (24.1 MPa) for Classes F2 and F3. Nonstructural concrete shall be air entrained in accordance with ACI 318.

    SECTION 1905—SEISMIC REQUIREMENTS

    1905.1 General. In addition to the provisions of ACI 318, structural concrete shall comply with the requirements of Section 1905.

    1905.2 ACI 318 Section 2.3. Modify existing definitions and add the following definitions to ACI 318 Section 2.3:

    CAST-IN-PLACE CONCRETE EQUIVALENT DIAPHRAGM. A cast-in-place noncomposite topping slab diaphragm, as defined in Section 18.12.5, or a diaphragm constructed with precast concrete components that uses closure strips between precast components with detailing that meets the requirements of ACI 318 for the Seismic Design Category of the structure.

    DETAILED PLAIN CONCRETE STRUCTURAL WALL. A wall complying with the requirements of Chapter 14, and Section 1905.5 of the California Building Code .

    ORDINARY PLAIN CONCRETE STRUCTURAL WALL. A wall complying with the requirements of Chapter 14, excluding 14.6.2.

  • CBC § 1903A.4 High relevance — show source text

    1903A.4 Steel fiber reinforcement – Not permitted.

    1903A.5 Welding of reinforcing bars - Modify ACI 318 Section 26.6.4.2(b) by adding the following:

    Subject to prior approval of the enforcing agency, longitudinal holding wires, conforming to ASTM A1064 of maximum wire size W5, that are machine resistance welded to stirrup/tie cage (or spiral assemblies) consisting of low alloy steel reinforcing conforming to ASTM A706 are permitted when performed under continuous competent control in a fabrication shop. Tack welding of primary reinforcing bars together or to stirrups/ties is not permitted. Holding wire weld locations shall not occur on any longitudinal or primary reinforcing nor on any portion of a reinforcing bar that is or will be bent in accordance with ACI 318 Section 25.3 for the extents specified in AWS D1.4 Section 4.2.6.

    [DSA-SS] Exception: Mat reinforcing for slabs or isolated footings shall be permitted to have holding wires located no more than six bar diameters from the free end of reinforcing. Such free ends shall not be associated with any welded splices, couplers or other free- end modifications involving reinforcement development.

    Quality control tests shall be performed on shop-welded specimens by the fabricator. Reinforcing steel specimens containing the holding wire shall be tested for yield and tensile strength at the frequency required by Section 1910A.2. Test reports shall be available on request to the approved agency, design professional and enforcement agency.

    SECTION 1904 A —DURABILITY REQUIREMENTS

    1904 A .1 Structural concrete. Structural concrete shall conform to the durability requirements of ACI 318.

    1904 A .2 Nonstructural concrete. The registered design professional shall assign nonstructural concrete a freeze-thaw exposure class, as defined in ACI 318, based on the anticipated exposure of nonstructural concrete. Nonstructural concrete shall have a minimum specified compressive strength, f´ c, of 2,500 psi (17.2 MPa) for Class F0; 3,000 psi (20.7 MPa) for Class F1; and 3,500 psi (24.1 MPa) for Classes F2 and F3. Nonstructural concrete shall be air entrained in accordance with ACI 318.

    SECTION 1905 A —SEISMIC REQUIREMENTS

    1905 A .1 General. In addition to the provisions of ACI 318, structural concrete shall comply with the requirements of Section 1905 A .

    1905 A .2 ACI 318 Section 2.3. Modify existing definitions and add the following definitions to ACI 318 Section 2.3:

    CAST-IN-PLACE CONCRETE EQUIVALENT DIAPHRAGM. A cast-in-place noncomposite topping slab diaphragm, as defined in Section 18.12.5, or a diaphragm constructed with precast concrete components that uses closure strips between precast components with detailing that meets the requirements of ACI 318 for the Seismic Design Category of the structure.

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    CONCRETE

  • CBC § 25.4 High relevance — show source text

    The use of this table shall be prohibited for soil classifications not shown.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot per foot = 0.1571 kPa2/m, 1 pound per square inch = 6.895 kPa.
    NR = Not Required.
    DR = Design Required.
    a. Soil classes are in accordance with the Unified Soil Classification System. Refer to Table R401.4.1(2).
    b. Table values are based on reinforcing bars with a minimum yield strength of 60,000 psi.
    c. Vertical reinforcement with a yield strength of less than 60,000 psi and bars of a different size than specified in the table are permitted in accordance with Section
    R404.1.3.3.7.6 and Table R404.1.3.2(9).
    d. NR indicates vertical wall reinforcement is not required, except for 6-inch nominal walls formed with stay-in-place forming systems in which case vertical reinforcement shall
    be No. 4@48 inches on center.
    e. Allowable deflection criterion is_L_/240, where_L_ is the unsupported height of the basement wall in inches.
    f. Interpolation is not permitted.
    g. Where walls will retain 4 feet or more of unbalanced backfill, they shall be laterally supported at the top and bottom before backfilling.
    h. Vertical reinforcement shall be located to provide a cover of 11/4 inches measured from the inside face of the wall. The center of the steel shall not vary from the specified loca-
    tion by more than the greater of 10 percent of the wall thickness or3/8 inch.
    i. Concrete cover for reinforcement measured from the inside face of the wall shall be not less than3/4 inch. Concrete cover for reinforcement measured from the outside face of
    the wall shall be not less than 11/2 inches for No. 5 bars and smaller, and not less than 2 inches for larger bars.
    j. DR means design is required in accordance with the applicable building code, or in the absence of a code, in accordance with ACI 318.
    k. Concrete shall have a specified compressive strength,f′c, of not less than 2,500 psi at 28 days, unless a higher strength is required by Note l or m.
    l. The minimum thickness is permitted to be reduced 2 inches, provided that the minimum specified compressive strength of concrete,f′c, is 4,000 psi.
    m.A plain concrete wall with a minimum nominal thickness of 12 inches is permitted, provided that the minimum specified compressive strength of concrete,f′c, is 3,500 psi.
    n. See Table R608.3 for tolerance from nominal thickness permitted for flat walls.
    o. The use of this table shall be prohibited for soil classifications not shown.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot per foot = 0.1571 kPa2/m, 1 pound per square inch = 6.895 kPa.
    NR = Not Required.
    DR = Design Required.
    a. Soil classes are in accordance with the Unified Soil Classification System. Refer to Table R401.4.1(2).
    b. Table values are based on reinforcing bars with a minimum yield strength of 60,000 psi.
    c.

  • CBC § 25.4 High relevance — show source text

    The minimum thickness is permitted to be reduced 2 inches, provided that the minimum specified compressive strength of concrete,f′c, is 4,000 psi.
    m.A plain concrete wall with a minimum nominal thickness of 12 inches is permitted, provided that the minimum specified compressive strength of concrete,f′c, is 3,500 psi.
    n. See Table R608.3 for tolerance from nominal thickness permitted for flat walls.
    o. The use of this table shall be prohibited for soil classifications not shown.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot per foot = 0.1571 kPa2/m, 1 pound per square inch = 6.895 kPa.
    NR = Not Required.
    DR = Design Required.
    a. Soil classes are in accordance with the Unified Soil Classification System. Refer to Table R401.4.1(2).
    b. Table values are based on reinforcing bars with a minimum yield strength of 60,000 psi.
    c. Vertical reinforcement with a yield strength of less than 60,000 psi and bars of a different size than specified in the table are permitted in accordance with Section
    R404.1.3.3.7.6 and Table R404.1.3.2(9).
    d. NR indicates vertical wall reinforcement is not required, except for 6-inch nominal walls formed with stay-in-place forming systems in which case vertical reinforcement shall
    be No. 4@48 inches on center.
    e. Allowable deflection criterion is_L_/240, where_L_ is the unsupported height of the basement wall in inches.
    f. Interpolation is not permitted.
    g. Where walls will retain 4 feet or more of unbalanced backfill, they shall be laterally supported at the top and bottom before backfilling.
    h. Vertical reinforcement shall be located to provide a cover of 11/4 inches measured from the inside face of the wall. The center of the steel shall not vary from the specified loca-
    tion by more than the greater of 10 percent of the wall thickness or3/8 inch.
    i. Concrete cover for reinforcement measured from the inside face of the wall shall be not less than3/4 inch. Concrete cover for reinforcement measured from the outside face of
    the wall shall be not less than 11/2 inches for No. 5 bars and smaller, and not less than 2 inches for larger bars.
    j. DR means design is required in accordance with the applicable building code, or in the absence of a code, in accordance with ACI 318.
    k. Concrete shall have a specified compressive strength,f′c, of not less than 2,500 psi at 28 days, unless a higher strength is required by Note l or m.
    l. The minimum thickness is permitted to be reduced 2 inches, provided that the minimum specified compressive strength of concrete,f′c, is 4,000 psi.
    m.A plain concrete wall with a minimum nominal thickness of 12 inches is permitted, provided that the minimum specified compressive strength of concrete,f′c, is 3,500 psi.
    n. See Table R608.3 for tolerance from nominal thickness permitted for flat walls.
    o.

  • CBC § 17.2 High relevance — show source text

    1904 A .2 Nonstructural concrete. The registered design professional shall assign nonstructural concrete a freeze-thaw exposure class, as defined in ACI 318, based on the anticipated exposure of nonstructural concrete. Nonstructural concrete shall have a minimum specified compressive strength, f´ c, of 2,500 psi (17.2 MPa) for Class F0; 3,000 psi (20.7 MPa) for Class F1; and 3,500 psi (24.1 MPa) for Classes F2 and F3. Nonstructural concrete shall be air entrained in accordance with ACI 318.

    SECTION 1905 A —SEISMIC REQUIREMENTS

    1905 A .1 General. In addition to the provisions of ACI 318, structural concrete shall comply with the requirements of Section 1905 A .

    1905 A .2 ACI 318 Section 2.3. Modify existing definitions and add the following definitions to ACI 318 Section 2.3:

    CAST-IN-PLACE CONCRETE EQUIVALENT DIAPHRAGM. A cast-in-place noncomposite topping slab diaphragm, as defined in Section 18.12.5, or a diaphragm constructed with precast concrete components that uses closure strips between precast components with detailing that meets the requirements of ACI 318 for the Seismic Design Category of the structure.

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    CONCRETE

    PRECAST CONCRETE DIAPHRAGM. A diaphragm constructed with precast concrete components, with or without a cast-in-place topping, that includes the use of discrete connectors or joint reinforcement to transmit diaphragm forces.

    1905 A .3 Intermediate precast structural walls. Intermediate precast structural walls shall comply with Section 18.5 of ACI 318 and this section.

    1905 A .3.1 Connections designed to yield. Connections that are designed to yield shall be capable of maintaining 80 percent of their design strength at the deformation induced by the design displacement or shall use Type 2 mechanical splices. [DSA-SS] Connections between wall panels and the foundation shall be designed per Section 1617A.1.15.

    1905 A .4 Foundations designed to resist earthquake forces. Foundations resisting earthquake-induced forces or transferring earthquake-induced forces between a structure and the ground shall comply with the requirements of Section 18.13 of ACI 318 and other applicable provisions of ACI 318 unless modified by Chapter 18 A .

    1905 A .5 Detailed plain concrete structural walls. Not permitted.

    1905 A .6 Structural plain concrete. Not permitted.

    1905 A .7 Design requirements for anchors. For the design requirements for anchors, Sections 1905 A .7.1 and 1905 A .7.2 provide exceptions that are permitted to ACI 318.

    1905 A .7.1 Anchors in tension. The following exception is permitted to ACI 318 Section 17.10.5.2:

  • CBC § 722.2.4.1 High relevance — show source text

    The minimum dimension is permitted to be reduced to 8 inches for rectangular columns with two parallel sides not less than 36 inches in length.
    b. The minimum dimension is permitted to be reduced to 10 inches for rectangular columns with two parallel sides not less than 36 inches in length.|For SI: 1 inch = 25 mm.
    a. The minimum dimension is permitted to be reduced to 8 inches for rectangular columns with two parallel sides not less than 36 inches in length.
    b. The minimum dimension is permitted to be reduced to 10 inches for rectangular columns with two parallel sides not less than 36 inches in length.|For SI: 1 inch = 25 mm.
    a. The minimum dimension is permitted to be reduced to 8 inches for rectangular columns with two parallel sides not less than 36 inches in length.
    b. The minimum dimension is permitted to be reduced to 10 inches for rectangular columns with two parallel sides not less than 36 inches in length.|For SI: 1 inch = 25 mm.
    a. The minimum dimension is permitted to be reduced to 8 inches for rectangular columns with two parallel sides not less than 36 inches in length.
    b. The minimum dimension is permitted to be reduced to 10 inches for rectangular columns with two parallel sides not less than 36 inches in length.|For SI: 1 inch = 25 mm.
    a. The minimum dimension is permitted to be reduced to 8 inches for rectangular columns with two parallel sides not less than 36 inches in length.
    b. The minimum dimension is permitted to be reduced to 10 inches for rectangular columns with two parallel sides not less than 36 inches in length.|

    722.2.4.1 Minimum size. The minimum overall dimensions of reinforced concrete columns for fire-resistance ratings of 1 hour to 4 hours for exposure to fire on all sides shall comply with this section.

    722.2.4.1.1 Concrete strength less than or equal to 12,000 psi. For columns made with concrete having a specified compressive strength, f′ c, of less than or equal to 12,000 psi (82.7 MPa), the minimum dimension shall comply with Table 722.2.4.

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    FIRE AND SMOKE PROTECTION FEATURES

    722.2.4.1.2 Concrete strength greater than 12,000 psi. For columns made with concrete having a specified compressive strength, f’ c, greater than 12,000 psi (82.7 MPa), for fire-resistance ratings of 1 hour to 4 hours the minimum dimension shall be 24 inches (610 mm).

    722.2.4.2 Minimum cover for R/C columns. The minimum thickness of concrete cover to the main longitudinal reinforcement in columns, regardless of the type of aggregate used in the concrete and the specified compressive strength of concrete, f’ c, shall be not less than 1 inch (25 mm) times the number of hours of required fire resistance or 2 inches (51 mm), whichever is less.

  • CBC § 25.4 High relevance — show source text

    Concrete cover for reinforcement measured from the inside face of the wall shall be not less than3/4 inch. Concrete cover for reinforcement measured from the outside face of
    the wall shall be not less than 11/2 inches for No. 5 bars and smaller, and not less than 2 inches for larger bars.
    j. DR means design is required in accordance with the applicable building code, or in the absence of a code, in accordance with ACI 318.
    k. Concrete shall have a specified compressive strength,f′c, of not less than 2,500 psi at 28 days, unless a higher strength is required by Note l or m.
    l. The minimum thickness is permitted to be reduced 2 inches, provided that the minimum specified compressive strength of concrete,f′c, is 4,000 psi.
    m.A plain concrete wall with a minimum nominal thickness of 12 inches is permitted, provided that the minimum specified compressive strength of concrete,f′c, is 3,500 psi.
    n. See Table R608.3 for tolerance from nominal thickness permitted for flat walls.
    o. The use of this table shall be prohibited for soil classifications not shown.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot per foot = 0.1571 kPa2/m, 1 pound per square inch = 6.895 kPa.
    NR = Not Required.
    DR = Design Required.
    a. Soil classes are in accordance with the Unified Soil Classification System. Refer to Table R401.4.1(2).
    b. Table values are based on reinforcing bars with a minimum yield strength of 60,000 psi.
    c. Vertical reinforcement with a yield strength of less than 60,000 psi and bars of a different size than specified in the table are permitted in accordance with Section
    R404.1.3.3.7.6 and Table R404.1.3.2(9).
    d. NR indicates vertical wall reinforcement is not required, except for 6-inch nominal walls formed with stay-in-place forming systems in which case vertical reinforcement shall
    be No. 4@48 inches on center.
    e. Allowable deflection criterion is_L_/240, where_L_ is the unsupported height of the basement wall in inches.
    f. Interpolation is not permitted.
    g. Where walls will retain 4 feet or more of unbalanced backfill, they shall be laterally supported at the top and bottom before backfilling.
    h. Vertical reinforcement shall be located to provide a cover of 11/4 inches measured from the inside face of the wall. The center of the steel shall not vary from the specified loca-
    tion by more than the greater of 10 percent of the wall thickness or3/8 inch.
    i. Concrete cover for reinforcement measured from the inside face of the wall shall be not less than3/4 inch. Concrete cover for reinforcement measured from the outside face of
    the wall shall be not less than 11/2 inches for No. 5 bars and smaller, and not less than 2 inches for larger bars.
    j. DR means design is required in accordance with the applicable building code, or in the absence of a code, in accordance with ACI 318.
    k. Concrete shall have a specified compressive strength,f′c, of not less than 2,500 psi at 28 days, unless a higher strength is required by Note l or m.
    l.

  • CBC § 19-5 Medium relevance — show source text

    1903 Specifications for Tests and Materials . . . . . . . . . . . 19-5

    1904 Durability Requirements . . . . . . . . . . . . . . . . . . . . . . . 19-6

    1905 Seismic Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 19-6

    1906 Footings for Light-Frame Construction . . . . . . . . . . 19-8

    1907 Slabs-on-Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-8

    1908 Shotcrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-8

    1909 Additional Requirements for Community Colleges

    [DSA-SS/CC]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-8

    1910 Additional Requirements for Skilled Nursing Facilities, Intermediate Care Facilities, Acute Psychiatric and Non-GAC Buildings

    [OSHPD 1R, 2 & 5]. . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-12

    1911 Existing Concrete Structures [OSHPD 1R, 2 & 5]. . . . . . .19-13

    CHAPTER 19A CONCRETE . . . . . . . . . . . . . . . . . . . . . . . . . . 19A-1

    1901A General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19A-3

    1902A Coordination of Terminology . . . . . . . . . . . . . . . . . . . .19A-4

    1903A Specifications for Tests and Materials . . . . . . . . . . . .19A-4

    1904A Durability Requirements . . . . . . . . . . . . . . . . . . . . . . . .19A-4

    1905A Seismic Requirements . . . . . . . . . . . . . . . . . . . . . . . . . .19A-4

    1906A Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19A-5

    1907A Slabs-on-Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19A-5

    1908A Shotcrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19A-6

    1909A Modifications to ACI 318. . . . . . . . . . . . . . . . . . . . . . . . .19A-6

  • CBC § 1603.1 Medium relevance — show source text

    Construction documents 1603.1,

    1901.5 Durability 1904 Footings 1809, 1906 Foundation walls 1807.1.5, 1808.8 Materials 1705.3.2, 1901, 1903 Plain, structural 1906 Reinforced gypsum concrete 2514 Rodentproofing Appendix F Roof tile 1504.3, 1507.3, 1513 Shotcrete 1908 Slabs-on-ground 1907 Special inspections 1705.3, Table 1705.3 Specifications 1903 Strength testing 1705.3.2 Structural concrete with GFRP

    reinforcement 1901.2.1 Wood support 2304.13 Concrete Masonry Calculated fire resistance 722.3

    Construction 2104

    Design 2101.2, 2108, 2109 Materials 2103.1 Surface bonding 2103.2.2, 2109.2 Wood support 2304.13 Concrete Roof Tile 1504.3, 1507.3, 1513 Wind Resistance 1504.3, 1609.6.3.1 Condominium (see Apartment Houses) Conduit, Penetration Protection 713.3,

    1023.5 Conflicts in Code 102, 104.2.4.1 Congregate Living Facilities 310.2, 310.3, 310.4

    Construction (See Safeguards During Construction) Construction Documents 107, 1603 Alarms and detection 907.1.1

    Balconies 107.2.5

    Concrete construction 1901.5 Design load-bearing capacity 1803.6 Exterior walls 107.2.4

    Fire protection 107.2.2 Fire-resistant joint systems 715 Flood 107.2.6.1, 1603.1.7 Floor live load 1603.1.1

    Geotechnical 1603.1.6 Means of egress 107.2.3

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    Parking structures 402.4.1.3, 402.4.2.3 Perimeter line 402.1.1 Play structures 402.6.3, 424 Separation 402.4.2 Signs 402.6.4 Smoke control 402.7.2 Sprinkler protection 402.5 Standby power 402.7.3 Standpipe system 402.7.1, 905.3.3 Travel distance 402.8.5, 1006.2.1, 1006.3, 1017.2 Covered Walkway (see Pedestrian Walkway) 3104, 3306.7 Crawl Space

    Access 1209.1

    Drainage 1805.1.2 Unusable space fire protection 711.2.6 Ventilation 1202.4 Cripple Wall 2308.10.6, 2308.10.8.3, 2308.2.7, 2308.9.6 Cross-Laminated Timber 602.4, 602.4.4.2,

    2303.1.4

  • CBC § 1.1 Medium relevance — show source text

    1902 A .1.1 Design displacement. Design displacement shall be the Design Earthquake Displacement, δ DE, defined in ASCE 7 Section 12.8.6.3. For diaphragms that can be idealized as rigid in accordance with ASCE 7 Section 12.3.1.2, δ di, displacement due to diaphragm deformation corresponding to the design earthquake, is permitted to be taken as zero.

    SECTION 1903 A —SPECIFICATIONS FOR TESTS AND MATERIALS

    1903 A .1 General. Materials used to produce concrete, concrete itself and testing thereof shall comply with the applicable standards listed in ACI 318.

    1903 A .2 Glass fiber-reinforced concrete. Glass fiber-reinforced concrete (GFRC) and the materials used in such concrete shall be in accordance with the PCI 128.

    1903 A .3 Flat wall insulating concrete form (ICF) systems. Insulating concrete form material used for forming flat concrete walls shall conform to ASTM E2634. [OSHPD 1 & 4] Not permitted by OSHPD. [DSA-SS] ICF systems shall be considered alternative systems. Concrete constructed using ICF systems and attachments to ICF shall be designed for loads in accordance with this code and shall comply with manufacturer’s instructions and industry standards determined applicable by the enforcement agency. Calculations and drawings shall be submitted to the enforcement agency for review and approval prior to construction.

    1903A.4 Steel fiber reinforcement – Not permitted.

    1903A.5 Welding of reinforcing bars - Modify ACI 318 Section 26.6.4.2(b) by adding the following:

    Subject to prior approval of the enforcing agency, longitudinal holding wires, conforming to ASTM A1064 of maximum wire size W5, that are machine resistance welded to stirrup/tie cage (or spiral assemblies) consisting of low alloy steel reinforcing conforming to ASTM A706 are permitted when performed under continuous competent control in a fabrication shop. Tack welding of primary reinforcing bars together or to stirrups/ties is not permitted. Holding wire weld locations shall not occur on any longitudinal or primary reinforcing nor on any portion of a reinforcing bar that is or will be bent in accordance with ACI 318 Section 25.3 for the extents specified in AWS D1.4 Section 4.2.6.

    [DSA-SS] Exception: Mat reinforcing for slabs or isolated footings shall be permitted to have holding wires located no more than six bar diameters from the free end of reinforcing. Such free ends shall not be associated with any welded splices, couplers or other free- end modifications involving reinforcement development.

    Quality control tests shall be performed on shop-welded specimens by the fabricator. Reinforcing steel specimens containing the holding wire shall be tested for yield and tensile strength at the frequency required by Section 1910A.2. Test reports shall be available on request to the approved agency, design professional and enforcement agency.

    SECTION 1904 A —DURABILITY REQUIREMENTS

    1904 A .1 Structural concrete. Structural concrete shall conform to the durability requirements of ACI 318.

  • CBC § 18.10.6.2 Medium relevance — show source text

    (c) Where boundary members are not required by Section 18.10.6.2 or 18.10.6.3 minimum reinforcement parallel to the edges of all structural walls and the boundaries of all openings shall consist of twice the cross-sectional area of the minimum shear reinforce- ment required per lineal foot of wall. Horizontal extent of boundary element shall be in accordance with Section 18.10.6.4 (a), (b) and (c).

    1909A.1.9 ACI 318, Section 18.12.6. Add Section 18.12.6.2 to ACI 318 as follows:

    18.12.6.2 – Collector and boundary elements in topping slabs placed over precast floor and roof elements shall not be less than 3 inches (76 mm) or 6 d b thick, where d b is the diameter of the largest reinforcement in the topping slab.

    1909A.1.10 ACI 318, Section 19.2.1.1 and Table 19.2.1.1. Modify ACI 318, Section 19.2.1.1 and Table 19.2.1.1 as follows: 19.2.1.1 The value of f´ c shall be in be in accordance with (a) through (e): (a) Limits for f´ c in Table 19.2.1.1. Limits apply to both normalweight and lightweight concrete. (b) Durability requirements in Table 19.3.2.1. (c) Structural strength requirements. (d) f´ c for lightweight concrete in special moment frames and special structural walls, and their foundations, shall not exceed 5000 psi, unless demonstrated by experimental evidence that members made with lightweight concrete provide strength and toughness equal to or exceeding those of comparable members made with normalweight concrete of the same strength. (e) Reinforced normal weight concrete with specified compressive strength higher than 8,000 psi (55 MPa) shall be consid- ered as an alternative system.

    TABLE 19.2.1.1—LIMITS FOR f ′
    c    		 Col2
    APPLICATION MINIMUMf c′, psi
    General 3000
    Special moment frames
    Special structural walls with Grade 60 or 80 reinforcement    		 3000
    Special structural walls with Grade 100 reinforcement 5000
    Precast-nonprestressed driven piles
    Drilled shafts    		 4000
    Precast-prestressed driven piles 5000
    Shotcrete 4000

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    1909A.1.11 ACI 318, Table 21.2.2.[DSA-SS] Replace Table 21.2.2 as follows :

    |TABLE 21.2.2—STRENGTH REDUCTION FACTOR φ FOR MOMENT, AXIAL FORCE,

  • CBC § 18A-11 Medium relevance — show source text

    1808A Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-11

    1809A Shallow Foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-14

    1810A Deep Foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-15

    1811A Prestressed Rock and Soil Foundation

    Anchors [OSHPD 1R, 2 & 5] . . . . . . . . . . . . . . . . . . . . 18A-25

    1812A Earth Retaining Shoring . . . . . . . . . . . . . . . . . . . . . . . . 18A-26

    1813A Vibro Stone Columns for Ground

    Improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-29

    CHAPTER 19 CONCRETE. . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1

    1901 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-3

    1902 Coordination of Terminology . . . . . . . . . . . . . . . . . . . 19-5

    1903 Specifications for Tests and Materials . . . . . . . . . . . 19-5

    1904 Durability Requirements . . . . . . . . . . . . . . . . . . . . . . . 19-6

    1905 Seismic Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 19-6

    1906 Footings for Light-Frame Construction . . . . . . . . . . 19-8

    1907 Slabs-on-Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-8

    1908 Shotcrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-8

    1909 Additional Requirements for Community Colleges

    [DSA-SS/CC]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-8

    1910 Additional Requirements for Skilled Nursing Facilities, Intermediate Care Facilities, Acute Psychiatric and Non-GAC Buildings

    [OSHPD 1R, 2 & 5]. . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-12

    1911 Existing Concrete Structures [OSHPD 1R, 2 & 5]. . . . . . .19-13

  • CBC § 722.2.4.1 High relevance — show source text

    The minimum dimension is permitted to be reduced to 10 inches for rectangular columns with two parallel sides not less than 36 inches in length.|

    722.2.4.1 Minimum size. The minimum overall dimensions of reinforced concrete columns for fire-resistance ratings of 1 hour to 4 hours for exposure to fire on all sides shall comply with this section.

    722.2.4.1.1 Concrete strength less than or equal to 12,000 psi. For columns made with concrete having a specified compressive strength, f′ c, of less than or equal to 12,000 psi (82.7 MPa), the minimum dimension shall comply with Table 722.2.4.

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    722.2.4.1.2 Concrete strength greater than 12,000 psi. For columns made with concrete having a specified compressive strength, f’ c, greater than 12,000 psi (82.7 MPa), for fire-resistance ratings of 1 hour to 4 hours the minimum dimension shall be 24 inches (610 mm).

    722.2.4.2 Minimum cover for R/C columns. The minimum thickness of concrete cover to the main longitudinal reinforcement in columns, regardless of the type of aggregate used in the concrete and the specified compressive strength of concrete, f’ c, shall be not less than 1 inch (25 mm) times the number of hours of required fire resistance or 2 inches (51 mm), whichever is less.

    722.2.4.3 Tie and spiral reinforcement. For concrete columns made with concrete having a specified compressive strength, f’ c, greater than 12,000 psi (82.7 MPa), tie and spiral reinforcement shall comply with the following:

    1. The free ends of rectangular ties shall terminate with a 135-degree (2.4 rad) standard tie hook.
    2. The free ends of circular ties shall terminate with a 90-degree (1.6 rad) standard tie hook.
    3. The free ends of spirals, including at lap splices, shall terminate with a 90-degree (1.6 rad) standard tie hook.

    The hook extension at the free end of ties and spirals shall be the larger of six bar diameters and the extension required by Section 25.3.2 of ACI 318. Hooks shall project into the core of the column.

    722.2.4.4 Columns built into walls. The minimum dimensions of Table 722.2.4 do not apply to a reinforced concrete column that is built into a concrete or masonry wall provided that all of the following are met:

    1. The fire-resistance rating for the wall is equal to or greater than the required rating of the column.
    2. The main longitudinal reinforcing in the column has cover not less than that required by Section 722.2.4.2.
    3. Openings in the wall are protected in accordance with Section 716.

    Where openings in the wall are not protected as required by Section 716, the minimum dimension of columns required to have a fire-resistance rating of 3 hours or less shall be 8 inches (203 mm), and 10 inches (254 mm) for columns required to have a fire-resistance rating of 4 hours, regardless of the type of aggregate used in the concrete.

    722.2.4.5 Precast cover units for steel columns. See Section 722.5.1.4.

  • CBC § 1904.2 Medium relevance — show source text

    1904.2 Nonstructural concrete. The registered design professional shall assign nonstructural concrete a freeze-thaw exposure class, as defined in ACI 318, based on the anticipated exposure of nonstructural concrete. Nonstructural concrete shall have a minimum specified compressive strength, f´ c, of 2,500 psi (17.2 MPa) for Class F0; 3,000 psi (20.7 MPa) for Class F1; and 3,500 psi (24.1 MPa) for Classes F2 and F3. Nonstructural concrete shall be air entrained in accordance with ACI 318.

    SECTION 1905—SEISMIC REQUIREMENTS

    1905.1 General. In addition to the provisions of ACI 318, structural concrete shall comply with the requirements of Section 1905.

    1905.2 ACI 318 Section 2.3. Modify existing definitions and add the following definitions to ACI 318 Section 2.3:

    CAST-IN-PLACE CONCRETE EQUIVALENT DIAPHRAGM. A cast-in-place noncomposite topping slab diaphragm, as defined in Section 18.12.5, or a diaphragm constructed with precast concrete components that uses closure strips between precast components with detailing that meets the requirements of ACI 318 for the Seismic Design Category of the structure.

    DETAILED PLAIN CONCRETE STRUCTURAL WALL. A wall complying with the requirements of Chapter 14, and Section 1905.5 of the California Building Code .

    ORDINARY PLAIN CONCRETE STRUCTURAL WALL. A wall complying with the requirements of Chapter 14, excluding 14.6.2.

    ORDINARY PRECAST STRUCTURAL WALL. A precast wall complying with the requirements of Chapters 1 through 13, 15, 16 and 19 through 26.

    ORDINARY REINFORCED CONCRETE STRUCTURAL WALL. A cast-in-place wall complying with the requirements of Chapters 1 through 13, 15, 16 and 19 through 26.

    PRECAST CONCRETE DIAPHRAGM. A diaphragm constructed with precast concrete components, with or without a cast-in-place topping, that includes the use of discrete connectors or joint reinforcement to transmit diaphragm forces.

    1905.3 Intermediate precast structural walls. Intermediate precast structural walls shall comply with Section 18.5 of ACI 318 and this section.

    1905.3.1 Connections designed to yield. Connections that are designed to yield shall be capable of maintaining 80 percent of their design strength at the deformation induced by the design displacement or shall use Type 2 mechanical splices.

    1905.4 Foundations designed to resist earthquake forces. Foundations resisting earthquake-induced forces or transferring earthquake-induced forces between a structure and the ground shall comply with the requirements of Section 18.13 of ACI 318 and other applicable provisions of ACI 318 unless modified by Chapter 18.

    1905.5 Detailed plain concrete structural walls. Detailed plain concrete structural walls are walls conforming to the requirements of ordinary plain concrete structural walls and Section 1905.5.1. [OSHPD 1R, 2 & 5] Plain concrete shall not be permitted.

  • CBC § 19-12 Medium relevance — show source text

    The following samples of materials and tendons selected by the engineer or the designated testing laboratory from the prestress- ing steel at the plant or job site shall be furnished by the contractor and tested by an approved independent testing agency: 1. For wire, strand or bars, 7-foot-long (2134 mm) samples shall be taken of the coil of wire or strand reel or rods. A minimum of one random sample per 5,000 pounds (2270 kg) of each heat or lot used on the job shall be selected. 2. For prefabricated prestressing tendons other than bars, one completely fabricated tendon 10 feet (3048 mm) in length between grips with the anchorage assembly at one end shall be furnished for each size and type of tendon and anchorage assembly.

    Variations of the bearing plate size need not be considered.

    The anchorages of unbonded tendons shall develop at least 95 percent of the minimum specified ultimate strength of the prestressing steel. The total elongation of the tendon under ultimate load shall not be less than 2 percent measured in a minimum gage length of 10 feet (3048 mm).

    Anchorages of bonded tendons shall develop at least 90 percent of the minimum specified strength of the prestressing steel tested in an unbonded state. All couplings shall develop at least 95 percent of the minimum specified strength of the

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    prestressing steel and shall not reduce the elongation at rupture below the requirements of the tendon itself. 3. If the prestressing tendon is a bar, one 7-foot (2134 mm) length complete with one end anchorage shall be furnished and, in addition, if couplers are to be used with the bar, two 4-foot (1219 mm) lengths of bar fabricated to fit and equipped with one coupler shall be furnished. 4. Mill tests of materials used for end anchorages shall be furnished. In addition, at least one Brinnell hardness test shall be made of each thickness of bearing plate.

    1910.2.4 Composite construction cores. Cores of the completed composite concrete construction shall be taken to demonstrate the shear strength along the contact surfaces. The cores shall be tested when the cast-in-place concrete is approximately 28 days old and shall be tested by a shear loading parallel to the joint between the precast concrete and the cast-in-place concrete. The minimum unit shear strength of the contact surface area of the core shall not be less than 100 psi (689 kPa). At least one core shall be taken from each building for each 5,000 square feet (465 m [2] ) of area of composite concrete construction and not fewer than three cores shall be taken from each project. The architect or structural engineer in responsible charge of the proj- ect or his or her representative shall designate the location for sampling.

    1910.3 Modifications to ACI 318.

    1910.3.1 ACI 318, Section 12.7.3. Add Section 12.7.3.4 to ACI 318 as follows:

  • CBC § 1903.1 Medium relevance — show source text

    SECTION 1903—SPECIFICATIONS FOR TESTS AND MATERIALS

    1903.1 General. Materials used to produce concrete, concrete itself and testing thereof shall comply with the applicable standards listed in ACI 318.

    Exception: The following standards as referenced in Chapter 35 shall be permitted to be used.

    1. ASTM C150

    2. ASTM C595

    3. ASTM C1157

    1903.2 Glass fiber-reinforced concrete. Glass fiber-reinforced concrete (GFRC) and the materials used in such concrete shall be in accordance with the PCI 128.

    1903.3 Flat wall insulating concrete form (ICF) systems. Insulating concrete form material used for forming flat concrete walls shall conform to ASTM E2634. [OSHPD 1R, 2 & 5] Not Permitted by OSHPD.

    1903.4 Steel fiber reinforcement - [OSHPD 1R, 2 & 5] Not permitted by OSHPD.

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    1903.5 Welding of reinforcing bars - [OSHPD 1R, 2 & 5] Modify ACI 318 Section 26.6.4.1(b) by adding the following:

    Subject to prior approval of the enforcing agency, longitudinal holding wires conforming to ASTM A1064, of maximum wire size W5, that are machine resistance welded to stirrup/tie cage (or spiral assemblies) consisting of low alloy steel reinforcing conforming to ASTM A706 are permitted when performed under continuous competent control in a fabrication shop. Tack welding of primary rein- forcing bars together or to stirrups/ties is not permitted. Holding wire weld locations shall not occur on any longitudinal or primary reinforcing nor on any portion of a reinforcing bar that is or will be bent in accordance with ACI 318 Section 25.3 for the extents speci- fied in AWS D1.4 Section 4.2.6.

    Quality control tests shall be performed on shop welded specimens by the fabricator. Reinforcing steel specimens containing the holding wire shall be tested for yield and tensile strength at the frequency required by Section 1910.2. Test reports shall be available on request to the approved agency, design professional and enforcement agency.

    SECTION 1904—DURABILITY REQUIREMENTS

    1904.1 Structural concrete. Structural concrete shall conform to the durability requirements of ACI 318.

    Exception: For Group R-2 and R-3 occupancies not more than three stories above grade plane, the specified compressive strength, f´ c, for concrete in basement walls, foundation walls, exterior walls and other vertical surfaces exposed to the weather shall be not less than 3,000 psi (20.7 MPa).

Frequently asked questions

Who assigns the exposure class for nonstructural concrete?

The registered design professional assigns the freeze–thaw exposure class per CBC §1904.2; the CBC enforces the resulting minimum f′c and air‑entrainment requirements .

Does CBC list exact cover depths for reinforcement?

Not in §1904 itself. The CBC requires structural concrete to conform to the durability provisions of ACI 318, and those ACI provisions contain the cover tables. So consult ACI 318 (as adopted) or the enforcement agency for the exact cover values (CBC §1904.1) .

What minimum compressive strength should I specify for a nonstructural exterior concrete curb likely to freeze?

Determine the ACI exposure class (F0–F3). If it’s F2 or F3 (freeze–thaw exposure), CBC §1904.2 requires f′c ≥ 3,500 psi and air entrainment per ACI 318 .

Are there any simplified minima for small apartment buildings?

Yes — for Group R‑2 and R‑3 occupancies ≤ 3 stories, basement walls, foundation walls, exterior walls and other vertical weather‑exposed surfaces must have f′c ≥ 3,000 psi (CBC §1904.1 exception) .

If ACI 318 and CBC conflict, which governs?

The CBC adopts and modifies ACI 318 in specific places; follow the CBC text (including any California modifications) and the referenced ACI provisions as adopted by the CBC. Consult the enforcement agency where interpretations are required (CBC §1904 and related adoption language) .

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