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Chapter 18A — SOILS AND FOUNDATIONS

Section 1806A — PRESUMPTIVE LOAD-BEARING VALUES OF SOILS

2025 California Building Code (Title 24, Part 2) · 2025 edition · updated 2026-07-29 · California

Italicized text is a California amendment to the model code, as printed in the official publication.

1806 A .1 Load combinations. The presumptive load-bearing values provided in Table 1806 A .2 shall be used with the allowable stress design load combinations specified in ASCE 7, Section 2.4 or the alternative allowable stress design load combinations of Section 1605 A .2. The values of vertical foundation pressure and lateral bearing pressure given in Table 1806 A .2 shall be permitted to be increased by one-third where used with the alternative allowable stress design load combinations of Section 1605 A .2 that include wind or earthquake loads.

1806 A .2 Presumptive load-bearing values. The load-bearing values used in design for supporting soils and rock near the surface shall not exceed the values specified in Table 1806 A .2 unless data to substantiate the use of higher values are submitted and approved. Where the building official has reason to doubt the classification, strength or compressibility of the soil or rock, the requirements of Section 1803 A .5.2 shall be satisfied.

Presumptive load-bearing values shall apply to materials with similar physical and engineering characteristics. Mud, organic silt and organic clays (OL, OH), peat (Pt) and undocumented fill shall not be assumed to have a presumptive load-bearing capacity unless data to substantiate the use of such a value are submitted.

Exception: A presumptive load-bearing capacity shall be permitted to be used where the building official deems the load-bearing capacity is adequate for the support of lightweight or temporary structures.

TABLE 1806A.2—PRESUMPTIVE LOAD-BEARING VALUES

CLASS OF MATERIALS VERTICAL
FOUNDATION
PRESSURE
(psf)		 LATERAL
BEARING PRESSURE
(psf/ft below natural grade)		 LATERAL SLIDING RESISTANCE LATERAL SLIDING RESISTANCE
CLASS OF MATERIALS VERTICAL
FOUNDATION
PRESSURE
(psf)		 LATERAL
BEARING PRESSURE
(psf/ft below natural grade)		 Coefficient of
frictiona		 Cohesion (psf)b
1. Crystalline bedrock 12,000 1,200 0.70 —
2. Sedimentary and foliated rock 4,000 400 0.35 —
3. Sandy gravel and gravel (GW and GP) 3,000 200 0.35 —
4. Sand, silty sand, clayey sand, silty gravel and
clayey gravel (SW, SP, SM, SC, GM and GC)		 2,000 150 0.25 —
5. Clay, sandy clay, silty clay, clayey silt, silt and
sandy silt (CL, ML, MH and CH)		 1,500 100 — 130
For SI: 1 pound per square foot = 0.0479 kPa, 1 pound per square foot per foot = 0.157 kPa/m.
a. Coefficient to be multiplied by the dead load.
b. Cohesion value to be multiplied by the contact area, as limited by Section 1806_A_.3.2.

1806 A .3 Lateral load resistance. Where the presumptive values of Table 1806 A .2 are used to determine resistance to lateral loads, the calculations shall be in accordance with Sections 1806 A .3.1 through 1806 A .3.4.

1806 A .3.1 Combined resistance. The total resistance to lateral loads shall be permitted to be determined by combining the values derived from the lateral bearing pressure and the lateral sliding resistance specified in Table 1806 A .2.

1806 A .3.2 Lateral sliding resistance limit. For clay, sandy clay, silty clay, clayey silt, silt and sandy silt, the lateral sliding resistance shall not exceed one-half the dead load.

1806 A .3.3 Increase for depth. The lateral bearing pressures specified in Table 1806 A .2 shall be permitted to be increased by the tabular value for each additional foot (305 mm) of depth to a value that is not greater than 15 times the tabular value.

1806 A .3.4 Increase for poles. Isolated poles for uses such as flagpoles or signs and poles used to support buildings that are not adversely affected by a [1] / 2 -inch (12.7 mm) motion at the ground surface due to short-term lateral loads shall be permitted to be designed using lateral bearing pressures equal to two times the tabular values.

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

SOILS AND FOUNDATIONS

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▸ Contents — 2025 California Building Code (Title 24, Part 2)
2025 California Building Code (Title 24, Part 2)
  1. Chapter 1 — ADMINISTRATION
  2. Chapter 2 — DEFINITIONS
  3. Chapter 3 — OCCUPANCY CLASSIFICATION AND USE
  4. Chapter 4 — SPECIAL DETAILED REQUIREMENTS BASED ON OCCUPANCY A…
  5. Chapter 5 — GENERAL BUILDING HEIGHTS AND AREAS
  6. Chapter 6 — TYPES OF CONSTRUCTION
  7. Chapter 7 — FIRE AND SMOKE PROTECTION FEATURES
  8. Chapter 7A — MATERIALS AND CONSTRUCTION METHODS FOR EXTERIOR W…
  9. Chapter 8 — INTERIOR FINISHES
  10. Chapter 9 — FIRE PROTECTION AND LIFE SAFETY SYSTEMS
  11. Chapter 10 — MEANS OF EGRESS
  12. Chapter 11 — RESERVED
  13. Chapter 11A — HOUSING ACCESSIBILITY
  14. Chapter 11B — ACCESSIBILITY TO PUBLIC BUILDINGS, PUBLIC ACCOMM…
  15. Chapter 12 — INTERIOR ENVIRONMENT
  16. Chapter 13 — ENERGY EFFICIENCY
  17. Chapter 14 — EXTERIOR WALLS
  18. Chapter 15 — ROOF ASSEMBLIES AND ROOFTOP STRUCTURES
  19. Chapter 16 — STRUCTURAL DESIGN
  20. Chapter 16A — STRUCTURAL DESIGN
  21. Chapter 17 — SPECIAL INSPECTIONS AND TESTS
  22. Chapter 17A — SPECIAL INSPECTIONS AND TESTS
  23. Chapter 18 — SOILS AND FOUNDATIONS
  24. ▸ Chapter 18A — SOILS AND FOUNDATIONS
    Overview
    1. Section 1801A — GENERAL
    2. Section 1802A — DESIGN BASIS
    3. Section 1803A — GEOTECHNICAL INVESTIGATIONS
    4. Section 1804A — EXCAVATION, GRADING AND FILL
    5. Section 1805A — DAMPPROOFING AND WATERPROOFING
    6. Section 1806A — PRESUMPTIVE LOAD-BEARING VALUES OF SOILS
    7. Section 1807A — FOUNDATION WALLS, RETAINING WALLS AND EMBEDDED…
    8. Section 1808A — FOUNDATIONS
    9. Section 1809A — SHALLOW FOUNDATIONS
    10. Section 1810A — DEEP FOUNDATIONS
    11. Section 1811A — PRESTRESSED ROCK AND SOIL FOUNDATION ANCHORS
    12. Section 1812A — EARTH RETAINING SHORING
    13. Section 1813A — VIBRO STONE COLUMNS FOR GROUND IMPROVEMENT
  25. Chapter 19 — CONCRETE
  26. Chapter 19A — CONCRETE
  27. Chapter 20 — ALUMINUM
  28. Chapter 21 — MASONRY
  29. Chapter 21A — MASONRY
  30. Chapter 22 — STEEL
  31. Chapter 22A — STEEL
  32. Chapter 23 — WOOD
  33. Chapter 24 — GLASS AND GLAZING
  34. Chapter 25 — GYPSUM PANEL PRODUCTS AND PLASTER
  35. Chapter 26 — PLASTIC
  36. Chapter 27 — ELECTRICAL
  37. Chapter 28 — MECHANICAL SYSTEMS
  38. Chapter 29 — PLUMBING SYSTEMS
  39. Chapter 30 — ELEVATORS AND CONVEYING SYSTEMS
  40. Chapter 31 — SPECIAL CONSTRUCTION
  41. Chapter 31A — SYSTEMS FOR WINDOW CLEANING OR EXTERIOR BUILDING…
  42. Chapter 31B — PUBLIC POOLS
  43. Chapter 31C — RADIATION
  44. Chapter 31D — FOOD ESTABLISHMENTS
  45. Chapter 31F — MARINE OIL TERMINALS
  46. Chapter 32 — ENCROACHMENTS INTO THE PUBLIC RIGHT-OF-WAY
  47. Chapter 33 — SAFEGUARDS DURING CONSTRUCTION
  48. Chapter 34 — RESERVED
  49. Chapter 35 — REFERENCED STANDARDS
  50. Appendix A — EMPLOYEE QUALIFICATIONS
  51. Appendix B — BOARD OF APPEALS
  52. Appendix C — GROUP U—AGRICULTURAL BUILDINGS
  53. Appendix D — FIRE DISTRICTS
  54. Appendix E — RESERVED
  55. Appendix F — RODENTPROOFING
  56. Appendix G — FLOOD-RESISTANT CONSTRUCTION
  57. Appendix H — SIGNS
  58. Appendix I — PATIO COVERS
  59. Appendix J — GRADING
  60. Appendix K — GROUP R-3 AND GROUP R-3.1 OCCUPANCIES PROTECTED B…
  61. Appendix L — EARTHQUAKE RECORDING INSTRUMENTATION
  62. Appendix M — TSUNAMI-GENERATED FLOOD HAZARDS
  63. Appendix N — REPLICABLE BUILDINGS
  64. Appendix O — PERFORMANCE-BASED APPLICATION
  65. Appendix P — SLEEPING LOFTS
  66. Appendix Q — EMERGENCY HOUSING

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