CBC · California Building Code

What are the CBC rules for slabs-on-ground (design, diaphragm, special cases)?

For homeowners: The CBC says slabs-on-ground that carry wall or foundation loads are “structural” and must be designed to ACI 318; otherwise nonstructural slabs must still be at least 3½" thick and generally have a 6‑mil vapor barrier unless a listed exception applies (§ 1907.1–1907.4) .

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Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

The California Building Code (CBC) treats slabs-on-ground as either structural or nonstructural and prescribes different obligations accordingly. Slabs that carry vertical or lateral loads from the structure or transmit loads to foundations must comply with the chapter's structural concrete provisions and ACI 318 as applicable (§ 1907.1) . Nonstructural slabs must still meet basic durability, minimum thickness and vapor‑retarder requirements (see §§ 1907.2–1907.4) .

Requirements in detail

Classification: structural vs. nonstructural

Structural slabs-on-ground: any slab required by ACI 318 to be treated as structural, or any slab designed to transmit vertical or lateral loads from other parts of the structure to the soil or to foundations — must comply with this chapter's structural concrete provisions and ACI 318 (§ 1907.1) .
Nonstructural slabs-on-ground: are governed by the more limited set of provisions called out in § 1907.2 (they still must meet durability rules and the thickness/vapor-retarder rules in §§ 1907.3 and 1907.4) . Portions of otherwise nonstructural slabs that will resist uplift or overturning must be designed in accepted engineering practice for those portions (§ 1907.2) .

Minimum physical requirements (decision‑relevant dimensions/values)

Item	Required value / description	Code reference
Minimum thickness for slabs-on-ground	3 1/2 inches (89 mm) minimum	§ 1907.3
Vapor retarder material and lap	6‑mil polyethylene (0.006 in; 0.15 mm) with joints lapped not less than 6 in (152 mm) placed between base course/subgrade and slab (or approved equivalent)	§ 1907.4
Exceptions to vapor retarder (categories)	Detached accessory R‑3 structures (garages, unheated utility buildings), small unheated storage rooms <70 ft², carports attached to R‑3, driveways/walks/patios not likely to be enclosed later, or when approved based on local site conditions	§ 1907.4, Exceptions 1–5
When slab is “structural”	When ACI 318 requires structural treatment OR slab transmits vertical/lateral loads from other parts of structure to soil or to foundations	§ 1907.1

Diaphragm function and design (what the CBC says)

The CBC explicitly recognizes slabs-on-ground as structural concrete when they are required to transmit loads (see § 1907.1) and in that case they must comply with all applicable chapter provisions and ACI 318. The CBC text does not reproduce the detailed diaphragm design rules from ACI 318; rather it defers to ACI 318 and the chapter for structural slab design (§ 1907.1) .
In short: if a slab-on-ground is intended to act as a diaphragm or to provide lateral restraint/support to walls/foundations, treat it as structural and design per the structural concrete provisions and ACI 318; the CBC does not restate ACI 318 diaphragm calculations in § 1907 itself (§ 1907.1) .

Durability and related requirements

Nonstructural slabs must meet the chapter durability requirements referenced in § 1907.2 (see § 1904 for durability provisions) and must follow the minimum thickness and vapor retarder rules noted above (§ 1907.2, § 1907.3, § 1907.4) file.
Where slabs provide lateral support for stem walls or resist uplift/overturning, the required portion must be designed by accepted engineering practice (this moves toward structural design) (§ 1907.2) .

Exceptions & special cases

Vapor retarder exceptions (explicit): detached accessory R‑3 structures (garages, unheated utility buildings), unheated storage rooms <70 ft², attached carports to R‑3, driveways/walks/patios that will not later be enclosed, or where approved based on local site conditions (§ 1907.4, Exceptions 1–5) .
Portions of a nonstructural slab used to resist uplift or overturning must be engineered for those forces throughout the dead‑load portion resisting uplift (i.e., even a “nonstructural” slab may require engineering where uplift/overturning is an issue) (§ 1907.2) .
If the slab supports structural elements (e.g., bearing walls, concentrated foundations, retaining wall support, or concentrated loads from equipment), it is structural under § 1907.1 and ACI 318 applies; the CBC does not provide alternate simplified rules for diaphragms in § 1907 itself — those details are in the referenced structural provisions and standards (§ 1907.1) .

Common mistakes

Assuming all slabs-on-ground are “nonstructural.” If the slab transmits loads to the soil or supports other parts of the structure it’s structural and must meet the chapter’s structural concrete requirements and ACI 318 (§ 1907.1) .
Using slab thickness less than 3 1/2 in. for interior floor slabs without verifying the slab is nonstructural and the intended use (minimum thickness mandated by § 1907.3) .
Omitting a vapor retarder where required — § 1907.4 specifies a 6‑mil polyethylene or approved equivalent and lap details; the code also lists the limited exceptions and local‑condition approvals (§ 1907.4) .
Failing to design nonstructural slab portions that resist uplift/overturning — § 1907.2 requires accepted engineering practice for those portions even when the slab is otherwise nonstructural .
Expecting the CBC § 1907 text to include full diaphragm design equations or reinforcement schedules — the CBC defers to ACI 318 and the structural-concrete provisions for those details (§ 1907.1) .

Worked example — concrete scenario applying the rule with numbers

Scenario: You are designing a 1,200 ft² single‑story, unheated, detached garage (Group R‑3 accessory) slab-on-ground that will support light vehicle loads and the garage walls (sill plate and light framing). Decide whether the slab is structural and what CBC minimum requirements apply.

Step 1 — Is the slab structural? Because the slab will transmit vertical loads from the garage walls and vehicles to the soil, it is acting to transmit vertical loads and therefore meets the CBC definition of a structural slab-on-ground; § 1907.1 requires such slabs to comply with the chapter's structural concrete provisions and ACI 318 (§ 1907.1) .

Step 2 — Minimum thickness and vapor retarder: Even if the slab were nonstructural, the minimum thickness is 3 1/2 in (89 mm) (§ 1907.3) — but as structural, you must follow ACI 318 and the chapter provisions for thickness, reinforcement and joints; CBC § 1907.1 directs you to treat the slab per the structural provisions and ACI 318 (§ 1907.1, § 1907.3) .

Step 3 — Vapor retarder: Detached accessory to R‑3 (garage) is one of the explicit exceptions for vapor retarder in § 1907.4 Exception 1, so a 6‑mil vapor retarder is not required by that clause; however, because the slab is structural and will support walls and vehicles, good practice — and in many jurisdictions required engineering — will still call for a subgrade treatment/vapor control and proper reinforcement per ACI 318 and local practice (§ 1907.1, § 1907.4 Exception 1) .

Net result: Design the garage slab per structural concrete provisions (ACI 318) for reinforcement, thickness and load transfer because it transmits vertical loads (§ 1907.1). You may omit the 6‑mil vapor retarder by the CBC exception for detached R‑3 accessory structures (§ 1907.4 Exception 1), but coordinate with the local building official and geotechnical recommendations (§ 1907.4) .

Related provisions

§ 1907.1 — Structural slabs-on-ground (classification and requirement to comply with chapter/ACI 318)
§ 1907.2 — Nonstructural slabs-on-ground (requirements and uplift/overturning treatment)
§ 1907.3 — Thickness (minimum 3 1/2 in)
§ 1907.4 — Vapor retarder requirements and exceptions (6‑mil polyethylene, 6 in lap)
§ 1904 — Durability requirements referenced for slabs (§ 1907.2 references durability; see chapter durability provisions)
§ 1906 — Footings for light‑frame construction (related where slabs tie into footings or stem walls)
§ 1705 — Special inspection requirements (applies where special inspection of concrete and anchors is required by chapter/ACI 318)
§ 1909A — Modifications to ACI 318 (where ACI 318 text is modified by the CBC)

Code references

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

CBC § 2.4. High relevance — show source text
2.4. Anchors are located a minimum of 15 anchor diameters from the edge of the concrete perpendicular to the length of the track. 2.5. The track is 33 to 68 mil (0.84 mm to 1.73 mm) designation thickness. 3. In light-frame construction bearing or nonbearing walls, shear strength of concrete anchors less than or equal to 1 inch (25 mm) in diameter attaching sill plate or track to foundation or foundation stemwalls need not satisfy Sections 17.10.6.3(a) through (c) when the design strength of the anchors is determined in accordance with Section 17.7.2.1(c) of ACI 318.

SECTION 1906—FOOTINGS FOR LIGHT-FRAME CONSTRUCTION

[OSHPD 1R, 2 & 5] Plain concrete footings not permitted by OSHPD.

1906.1 Plain concrete footings. For Group R-3 occupancies and buildings of other occupancies less than two stories above grade plane of light-frame construction, the required thickness of plain concrete footings is permitted to be 6 inches (152 mm), provided that the footing does not extend more than 4 inches (102 mm) on either side of the supported wall.

SECTION 1907—SLABS-ON-GROUND

1907.1 Structural slabs-on-ground. Structural concrete slabs-on-ground shall comply with all applicable provisions of this chapter. Slabs-on-ground shall be considered structural concrete where required by ACI 318 or where designed to transmit either of the following:
1. Vertical loads or lateral forces from other parts of the structure to the soil.
2. Vertical loads or lateral forces from other parts of the structure to foundations.
1907.2 Nonstructural slabs-on-ground. Nonstructural slabs-on-ground shall be required to comply with Sections 1904.2, 1907.3 and 1907.4. Portions of the nonstructural slabs-on-ground used to resist uplift forces or overturning shall be designed in accordance with accepted engineering practice throughout the entire portion designated as dead load to resist uplift forces or overturning. 1907.3 Thickness. The thickness of concrete floor slabs supported directly on the ground shall be not less than 3 [1] / 2 inches (89 mm).

1907.4 Vapor retarder. A 6-mil (0.006 inch; 0.15 mm) polyethylene vapor retarder with joints lapped not less than 6 inches (152 mm) shall be placed between the base course or subgrade and the concrete floor slab, or other approved equivalent methods or materials shall be used to retard vapor transmission through the floor slab.

Exception: A vapor retarder is not required:
1. For detached structures accessory to occupancies in Group R-3, such as garages, utility buildings or other unheated facilities.
2. For unheated storage rooms having an area of less than 70 square feet (6.5 m [2] ) and carports attached to occupancies in Group R-3.
3. For buildings of other occupancies where migration of moisture through the slab from below will not be detrimental to the intended occupancy of the building.
4. For driveways, walks, patios and other flatwork that will not be enclosed at a later date.
5. Where approved based on local site conditions.
CBC § 3.1. High relevance — show source text
Allowable in-plane shear strength of exempt anchors, parallel to the edge of concrete, shall be permitted to be determined in accordance with AISI S100 Section J3.3.1.

2.1. The maximum anchor nominal diameter is [5] / 8 inch (16 mm). 2.2. Anchors are embedded into concrete a minimum of 7 inches (178 mm). 2.3. Anchors are located a minimum of 1 [3] / 4 inches (45 mm) from the edge of the concrete parallel to the length of the track.

2.4. Anchors are located a minimum of 15 anchor diameters from the edge of the concrete perpendicular to the length of the track. 2.5. The track is 33 to 68 mil (0.84 mm to 1.73 mm) designation thickness. 3. In light-frame construction bearing or nonbearing walls, shear strength of concrete anchors less than or equal to 1 inch (25 mm) in diameter attaching sill plate or track to foundation or foundation stemwalls need not satisfy Sections 17.10.6.3(a) through (c) when the design strength of the anchors is determined in accordance with Section 17.7.2.1(c) of ACI 318.

SECTION 1906 A — RESERVED

SECTION 1907 A —SLABS-ON-GROUND

1907 A .1 Structural slabs-on-ground. Structural concrete slabs-on-ground shall comply with all applicable provisions of this chapter. Slabs-on-ground shall be considered structural concrete where required by ACI 318 or where designed to transmit either of the following:
1. Vertical loads or lateral forces from other parts of the structure to the soil.
2. Vertical loads or lateral forces from other parts of the structure to foundations.
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1907 A .2 Nonstructural slabs-on-ground. Nonstructural slabs-on-ground shall be required to comply with Sections 1904 A .2, 1907 A .3 and 1907 A .4. Portions of the nonstructural slabs-on-ground used to resist uplift forces or overturning shall be designed in accordance with accepted engineering practice throughout the entire portion designated as dead load to resist uplift forces or overturning. 1907 A .3 Thickness. The thickness of concrete floor slabs supported directly on the ground shall be not less than 3 [1] / 2 inches (89 mm).

1907 A .4 Vapor retarder. A 6-mil (0.006 inch; 0.15 mm) polyethylene vapor retarder with joints lapped not less than 6 inches (152 mm) shall be placed between the base course or subgrade and the concrete floor slab, or other approved equivalent methods or materials shall be used to retard vapor transmission through the floor slab.

Exception: A vapor retarder is not required:
1. For detached structures accessory to occupancies in Group R-3, such as garages, utility buildings or other unheated facilities.
CBC § 19A-5 High relevance — show source text
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1907 A .2 Nonstructural slabs-on-ground. Nonstructural slabs-on-ground shall be required to comply with Sections 1904 A .2, 1907 A .3 and 1907 A .4. Portions of the nonstructural slabs-on-ground used to resist uplift forces or overturning shall be designed in accordance with accepted engineering practice throughout the entire portion designated as dead load to resist uplift forces or overturning. 1907 A .3 Thickness. The thickness of concrete floor slabs supported directly on the ground shall be not less than 3 [1] / 2 inches (89 mm).

1907 A .4 Vapor retarder. A 6-mil (0.006 inch; 0.15 mm) polyethylene vapor retarder with joints lapped not less than 6 inches (152 mm) shall be placed between the base course or subgrade and the concrete floor slab, or other approved equivalent methods or materials shall be used to retard vapor transmission through the floor slab.

Exception: A vapor retarder is not required:
1. For detached structures accessory to occupancies in Group R-3, such as garages, utility buildings or other unheated facilities.
2. For unheated storage rooms having an area of less than 70 square feet (6.5 m [2] ) and carports attached to occupancies in Group R-3.
3. For buildings of other occupancies where migration of moisture through the slab from below will not be detrimental to the intended occupancy of the building.
4. For driveways, walks, patios and other flatwork that will not be enclosed at a later date.
5. Where approved based on local site conditions.
SECTION 1908 A —SHOTCRETE

1908 A .1 General. Shotcrete shall be in accordance with the requirements of ACI 318 and the provisions of ACI 506R. Preconstruction tests of one or more shotcrete mockup panels prepared in accordance with Section 1705A.3.9.2 are required. In addition to testing requirements in ACI 318, special inspection and testing shall be in accordance with Section 1705A.3.9. The evaluation of the shotcrete mockup panel to qualify bar clearance dimensions in accordance with ACI 318 Section 25.2.7 or contact lap splices in accordance with ACI 318 Section 25.5.1.7 shall be in accordance with the requirements of ACI 506.4R with a core quality category of Very Good given in ACI 506.6T.

Shotcrete construction shall be in accordance with the requirements of ACI 506.2.

SECTION 1909A—MODIFICATIONS TO ACI 318

1909A.1 General. The text of ACI 318 shall be modified as indicated in Sections 1909A.1.1 through 1909A.1.16.

1909A.1.1 ACI 318, Section 4.12.2.2. Modify ACI 318, Section 4.12.2.2 by adding the following:
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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INDEX

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 § 1.3. Medium relevance — show source text
The maximum anchor nominal diameter is [5] / 8 inch (16 mm). 1.3. Anchor bolts are embedded into concrete not less than 7 inches (178 mm). 1.4. Anchor bolts are located not less than 1¾ inches (45 mm) from the edge of the concrete parallel to the length of the wood sill plate. 1.5. Anchor bolts are located not less than 15 anchor diameters from the edge of the concrete perpendicular to the length of the wood sill plate. 1.6. The sill plate is 2-inch (51 mm) or 3-inch (76 mm) nominal thickness. 2. For the calculation of the in-plane shear strength of anchor bolts attaching cold-formed steel track of bearing or nonbearing walls of light-frame construction to foundations or foundation stemwalls, the in-plane shear strength in accordance with Sections 17.7.2 and 17.7.3 of ACI 318 need not be computed and 17.10.6.3 shall be deemed to be satisfied provided that all of the following are met:

Allowable in-plane shear strength of exempt anchors, parallel to the edge of concrete, shall be permitted to be determined in accordance with AISI S100 Section J3.3.1.

2.1. The maximum anchor nominal diameter is [5] / 8 inch (16 mm). 2.2. Anchors are embedded into concrete a minimum of 7 inches (178 mm).

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CONCRETE

2.3. Anchors are located a minimum of 1 [3] / 4 inches (45 mm) from the edge of the concrete parallel to the length of the track.

2.4. Anchors are located a minimum of 15 anchor diameters from the edge of the concrete perpendicular to the length of the track. 2.5. The track is 33 to 68 mil (0.84 mm to 1.73 mm) designation thickness. 3. In light-frame construction bearing or nonbearing walls, shear strength of concrete anchors less than or equal to 1 inch (25 mm) in diameter attaching sill plate or track to foundation or foundation stemwalls need not satisfy Sections 17.10.6.3(a) through (c) when the design strength of the anchors is determined in accordance with Section 17.7.2.1(c) of ACI 318.

SECTION 1906—FOOTINGS FOR LIGHT-FRAME CONSTRUCTION

[OSHPD 1R, 2 & 5] Plain concrete footings not permitted by OSHPD.

1906.1 Plain concrete footings. For Group R-3 occupancies and buildings of other occupancies less than two stories above grade plane of light-frame construction, the required thickness of plain concrete footings is permitted to be 6 inches (152 mm), provided that the footing does not extend more than 4 inches (102 mm) on either side of the supported wall.

SECTION 1907—SLABS-ON-GROUND

1907.1 Structural slabs-on-ground. Structural concrete slabs-on-ground shall comply with all applicable provisions of this chapter. Slabs-on-ground shall be considered structural concrete where required by ACI 318 or where designed to transmit either of the following:
1. Vertical loads or lateral forces from other parts of the structure to the soil.
2. Vertical loads or lateral forces from other parts of the structure to foundations.
CBC § 2205.1 Medium relevance — show source text
Cold-Formed Steel 2204

Cold-formed Stainless Steel 2205.1 Cutting and notching 2206.3 Light-frame construction 2206 Special inspection 1705.12.2, 1705.13.3, 1705.2.3, 1705.2.7 Combustible Dusts 307.4, 414.5.1, 426.1 Combustible Liquids 307.1, 307.4, 307.5, 414.2.5, 414.5.3, 415.9.2, 415.10.1, 418.6

Combustible Material

Concealed spaces 413.2, 718.5 Exterior side of exterior wall 1405 High-pile stock or rack storage 413.1, 910.2.2 Type I and Type II 603, 805 Combustible Projections 705.2, 705.2.3.1 Combustible Storage 413, 910.2.2 Common Path of Egress Travel 1006.2.1 Compartmentation Ambulatory care facilities 422.2, 422.3 Group I-2 407.5, 407.6 Group I-3 408.6 Laboratory suites 428.3 Underground buildings 405.4, 405.5.2 Compressed Gas 307.2, 415.11.8 Concealed Spaces 413.2, 718 Concrete Chapters 19 and 19A Anchorage 1901.3 Calculated fire resistance 722.2

Cellular 721.2

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
CBC § 0.77 Medium relevance — show source text
shall be_ greater than or equal to 5. 4. The width-to-thickness ratios for beam flanges shall not be less than 3. 5. The spacing for lateral bracing of wide flange beams, L b , shall include the length of the side plate at beam ends. 6. The extension of the side plates beyond the face of the column shall be within the range of 0.77d to 1.0d. 7. The gap-to-side plate thickness ratio shall range from 2.1 to 2.3.

Exception: The gap-to-side plate thickness ratio shall be permitted to be modified for moment connections with unequal beam sizes on opposite sides of the column or when orthogonal beams acting as drag connections frame into the side plate. 8. Demand critical fillet welds {2}, {5}, {5a} and {7} shall have Magnetic Particle Testing (MT) in accordance with AWS D1.1 for procedure, technique and acceptance. Inspect the beginning and end of these welds for a 6-inch length, plus any location along the length of the weld where a start and restart is visually noted for a distance of 6 inches on either side of the start/stop location.

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STEEL

2202A.4.3 Modifications to AISC 358 Chapter 11 Bolted Moment Connection. The bolted sideplate steel moment connection shall be permitted, provided: 1. The beams shall consist of either rolled or built-up wide flange sections. Columns shall consist of rolled or built-up wide flange sections or noncomposite built-up box or HSS with a minimum wall thickness of [3] / 4 inch (19 mm), or satisfy the requirements of width-to-thickness ratios of highly ductile members in AISC 341. 2. The biaxial dual-strong axis and column minor axis configurations of the moment connection shall be considered as an alternative system. 3. For SMF and IMF systems, on the sideplate standard or configuration A the U-shaped cover plates shall be used with the k dimension extension. The k dimension extension length is defined as beam depth d b /6, rounded to the nearest [1] / 2 inch (12.7 mm).

4. The hinge-to-hinge span to beam depth, L h /d, shall be greater than or equal to 4.5. 5. The width-to-thickness ratios for beam flanges shall not be less than 3.5. Exception: For width-to-thickness ratios less than 3.5 the C pr shall be calculated in accordance with that for welded side- plate connections but in no case shall the width-to-thickness ratio be less than 3.0. 6. The minimum bolt-to-bolt spacing shall not be less than 3 bolt diameters. 7. The extension of the side plates beyond the face of the column shall be within the range of 0.65d to 1.5d. 8. The gap-to-side plate thickness ratio shall range from 2.1 to 2.3.
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 § 1.3.2.2 Medium relevance — show source text
Where unbalanced backfill retained by the stem wall is less than or equal to 18 inches (457 mm), the stem wall and above-grade wall it supports shall be provided with vertical reinforcement in accordance with Section R608.6 and Table R608.6(1), R608.6(2) or R608.6(3) for above-grade walls. Where unbalanced backfill retained by the stem wall is greater than 18 inches (457 mm), the stem wall and above-grade wall it supports shall be provided with vertical reinforcement in accordance with Section R608.6 and Table R608.6(1).
1. Stem walls laterally supported at top. Concrete stem walls that are monolithic with slabs-on-ground or are otherwise laterally supported by slabs-on-ground shall be vertically reinforced in accordance with Section R608.6 and Table R608.6(1), R608.6(2) or R608.6(3) for above-grade walls. Where the unbalanced backfill retained by the stem wall is greater than 18 inches (457 mm), the connection between the stem wall and the slab-on-ground, and the portion of the slab-on-ground providing lateral support for the wall shall be designed in accordance with PCA 100 or with accepted engineering practice. Where the unbalanced backfill retained by the stem wall is greater than 18 inches (457 mm), the minimum nominal thickness of the wall shall be 6 inches (152 mm).
R404.1.3.2.2 Concrete foundation stem walls supporting light-frame above-grade walls. Concrete foundation stem walls that support light-frame above-grade walls shall be designed and constructed in accordance with this section.
1. Stem walls not laterally supported at top. Concrete stem walls that are not monolithic with slabs-on-ground or are not otherwise laterally supported by slabs-on-ground and retain 48 inches (1219 mm) or less of unbalanced fill, measured from the top of the wall, shall be constructed in accordance with Section R404.1.3. Foundation stem walls that retain more than 48 inches (1219 mm) of unbalanced fill, measured from the top of the wall, shall be designed in accordance with Sections R404.1.1 and R404.4.
2. Stem walls laterally supported at top. Concrete stem walls that are monolithic with slabs-on-ground or are otherwise laterally supported by slabs-on-ground shall be constructed in accordance with Section R404.1.3. Where the unbalanced backfill retained by the stem wall is greater than 48 inches (1219 mm), the connection between the stem wall and the slab-on-ground, and the portion of the slab-on-ground providing lateral support for the wall, shall be designed in accordance with PCA 100 or in accordance with accepted engineering practice.
R404.1.3.3 Concrete, materials for concrete, and forms. Materials used in concrete, the concrete itself and forms shall conform to requirements of this section or ACI 318.

R404.1.3.3.1 Compressive strength. The minimum specified compressive strength of concrete, f ′ c, shall comply with Section R402.2 and shall be not less than 2,500 psi (17.2 MPa) at 28 days in buildings assigned to Seismic Design Category A, B or C and 3,000 psi (20.5 MPa) in buildings assigned to Seismic Design Category D 0, D 1 or D 2 .

R404.1.3.3.2 Concrete mixing and delivery. Mixing and delivery of concrete shall comply with ASTM C94 or ASTM C685.
CBC § 1807.2.5.1 Medium relevance — show source text
1807.2.5.1 Where required. At retaining walls located within 36 inches (914mm) of walking surfaces, a guard shall be required between the walking surface and the open side of the retaining wall where the walking surface is located more than 30 inches (762 mm) measured vertically to the surface or grade below at any point within 36 inches (914mm) horizontally to the edge of the open side. Guards shall comply with Section 1607.9.

1807.2.5.2 Height. Required guards at retaining walls shall comply with the height requirements of Section 1015.3.

1807.2.5.3 Opening limitations. Required guards shall comply with the opening limitations of Section 1015.4.

1807.3 Embedded posts and poles. Designs to resist both axial and lateral loads employing posts or poles as columns embedded in earth or in concrete footings in earth shall be in accordance with Sections 1807.3.1 through 1807.3.3 or ASABE EP 486.3.

1807.3.1 Limitations. The design procedures outlined in this section are subject to the following limitations:
1. The frictional resistance for structural walls and slabs on silts and clays shall be limited to one-half of the normal force imposed on the soil by the weight of the footing or slab.
2. Posts embedded in earth shall not be used to provide lateral support for structural or nonstructural materials such as plaster, masonry or concrete unless bracing is provided that develops the limited deflection required.
Wood poles shall be treated in accordance with AWPA U1 for sawn timber posts (Commodity Specification A, Use Category 4B) and for round timber posts (Commodity Specification B, Use Category 4B).

1807.3.2 Design criteria. The depth to resist lateral loads shall be determined using the design criteria established in Sections 1807.3.2.1 through 1807.3.2.3, or by other methods approved by the building official.

1807.3.2.1 Nonconstrained. The following formula shall be used in determining the depth of embedment required to resist lateral loads where lateral constraint is not provided at the ground surface, such as by a rigid floor or rigid ground surface pavement, and where lateral constraint is not provided above the ground surface, such as by a structural diaphragm. Equation 18-1 d = 0.5 A {1 + [1 + (4.36 h/A )] [1/2] }

where:

A = 2.34 P /( S 1 b ).

b = Diameter of round post or footing or diagonal dimension of square post or footing, feet (m).

d = Depth of embedment in earth in feet (m) but not over 12 feet (3658 mm) for purpose of computing lateral pressure.

h = Distance in feet (m) from ground surface to point of application of “ P .”

P = Applied lateral force in pounds (kN).

S 1 = Allowable lateral soil-bearing pressure as set forth in Section 1806.2 based on a depth of one-third the depth of embedment in pounds per square foot (psf) (kPa).

1807.3.2.2 Constrained. The following formula shall be used to determine the depth of embedment required to resist lateral loads where lateral constraint is provided at the ground surface, such as by a rigid floor or slab-on-ground.

Equation 18-2
CBC § 2.25 Medium relevance — show source text
00|2.25|0.70|DR|3.70|1.05|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|33 mil cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|16|3.85|1.45|DR|DR|3.40|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|33 mil cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|24|3.40|DR|DR|DR|2.70|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#8 Screw|Steel thick-
ness plus 3
threads|12|3.00|1.80|DR|DR|3.00|0.65|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#8 Screw|Steel thick-
ness plus 3
threads|16|3.00|1.00|DR|DR|2.85|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#8 Screw|Steel thick-
ness plus 3
threads|24|2.85|DR|DR|DR|2.20|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|12|4.00|3.85|2.80|1.80|4.00|3.05|1.50|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|16|4.00|3.30|1.95|0.60|4.00|2.25|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|24|4.00|2.25|DR|DR|4.00|0.65|DR|DR| |For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
DR = Design Required, o.c. = on center.
a. Wood furring shall be spruce-pine-fir or any softwood species with a specific gravity of 0.42 or greater.
CBC § 550.5. Medium relevance — show source text
Installation of the embedded parts.|X|—|—|—| |11.|b. Completion of the continuity of reinforcement across joints.|X|—|—|—| |11.|c. Completion of connections in the field.|X|—|—|—| |12.|Inspect installation tolerances of precast concrete diaphragm
connections for compliance with ACI 550.5.|—|X|ACI 318: 26.13.1.3|—| |13.|Verify in-situ concrete strength, prior to stressing of tendons
in posttensioned concrete and prior to removal of shores and
forms from beams and structural slabs.|—|X|ACI 318:26.10.2,
26.11.2,26.13.3.3|—| |14.|Inspect formwork for shape, location and dimensions of the
concrete member being formed.|—|X|ACI 318:
26.11.1.2(b),
26.13.3.3|1909A.1.15,
[DSA-SS/CC]1909.3.9| |For SI: 1 inch = 25.4 mm.
a. Where applicable, see Section 1705_A_.13.
b. Specific requirements for special inspection shall be included in the research report for the anchor issued by an approved source in accordance with 26.13 in ACI 318, or other
qualification procedures. Where specific requirements are not provided, special inspection requirements shall be specified by the registered design professional and shall be
approved by the building official prior to the commencement of the work.
c. Installation of all adhesive anchors in horizontal and upwardly inclined positions shall be performed by an ACI/CRSI Certified Adhesive Anchor Installer, except where the factored
design tension on the anchors is less than 100 pounds and those anchors are clearly noted on the approved construction documents or where the anchors are shear dowels across
cold joints in slabs on grade where the slab is not part of the lateral force-resisting system.|For SI: 1 inch = 25.4 mm.
a. Where applicable, see Section 1705_A_.13.
b. Specific requirements for special inspection shall be included in the research report for the anchor issued by an approved source in accordance with 26.13 in ACI 318, or other
qualification procedures. Where specific requirements are not provided, special inspection requirements shall be specified by the registered design professional and shall be
approved by the building official prior to the commencement of the work.
c. Installation of all adhesive anchors in horizontal and upwardly inclined positions shall be performed by an ACI/CRSI Certified Adhesive Anchor Installer, except where the factored
design tension on the anchors is less than 100 pounds and those anchors are clearly noted on the approved construction documents or where the anchors are shear dowels across
cold joints in slabs on grade where the slab is not part of the lateral force-resisting system.|For SI: 1 inch = 25.4 mm.
a. Where applicable, see Section 1705_A_.13.
b. Specific requirements for special inspection shall be included in the research report for the anchor issued by an approved source in accordance with 26.13 in ACI 318, or other
qualification procedures. Where specific requirements are not provided, special inspection requirements shall be specified by the registered design professional and shall be
approved by the building official prior to the commencement of the work.
_c.

Frequently asked questions

Do all slabs-on-ground need reinforcement per CBC?

Not always. Whether a slab must be designed as structural (including reinforcement per ACI 318) depends on whether it transmits vertical or lateral loads from other parts of the structure to the soil or foundations; if so it is structural and must comply with the structural concrete provisions and ACI 318 (§ 1907.1) .

What is the absolute minimum thickness for a slab-on-ground?

The CBC sets a minimum thickness of 3 1/2 inches (89 mm) for concrete floor slabs supported directly on the ground (§ 1907.3) .

Is a vapor retarder always required under slabs?

CBC requires a 6‑mil polyethylene vapor retarder with 6 in lap unless the slab falls under one of several exceptions (detached R‑3 accessory structures, small unheated storage <70 ft², attached carports to R‑3, driveways/walks/patios not to be enclosed, or where local conditions permit) (§ 1907.4, Exceptions 1–5) .

If a nonstructural slab resists uplift, do I still need to design it?

Yes — portions of nonstructural slabs used to resist uplift or overturning must be designed in accordance with accepted engineering practice for the entire portion designated as dead load to resist uplift (§ 1907.2) .

Where are the detailed diaphragm design rules for slabs found?

The CBC § 1907 defers detailed structural diaphragm design to the chapter's structural concrete provisions and standards such as ACI 318 — § 1907.1 requires compliance with those documents for structural slabs but does not reproduce the detailed equations or reinforcement schedules itself (§ 1907.1) .

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