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Chapter 25 — GYPSUM BOARD, GYPSUM PANEL PRODUCTS AND PLASTER

Section 2508

California Building Code (Title 24, Part 2) · 2022 edition · updated 2026-09-12 · California

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

2508.1 General.

Gypsum board, gypsum panel products and gypsum plaster construction shall be of the materials listed in Tables 2506.2 and 2507.2. These materials shall be assembled and installed in compliance with the appropriate standards listed in Tables 2508.1 and 2511.1.1 and Chapter 35.

TABLE 2508.1 INSTALLATION OF GYPSUM CONSTRUCTION

MATERIAL STANDARD
Gypsum board and gypsum panel
products		 GA 216; ASTM C840
Gypsum sheathing and gypsum
panel products		 ASTM C1280
Gypsum veneer base ASTM C844
Interior lathing and furring ASTM C841
Steel framing for gypsum board and
gypsum panel products		 ASTM C754; C1007

2508.2 Limitations.

Gypsum wallboard or gypsum plaster shall not be used in any exterior surface where such gypsum construction will be exposed directly to the weather. Gypsum wallboard shall not be used where there will be direct exposure to water or continuous high humidity conditions. Gypsum sheathing shall be installed on exterior surfaces in accordance with ASTM C1280.

2508.2.1 Weather protection. Gypsum wallboard, gypsum lath or gypsum plaster shall not be installed until weather protection for the installation is provided.

Copyright © 2022 by, or licensed to, International Code Council, Inc. (ALL RIGHTS RESERVED); licensed to California Building Standards Commission pursuant to License Agreement. No further reproductions is authorized. Any unauthorized reproduction or distribution is a violation of the federal copyright act and the license agreement, and subject to civil and criminal penalties thereunder.

GYPSUM BOARD, GYPSUM PANEL PRODUCTS AND PLASTER

TABLE 2507.2 LATH, PLASTERING MATERIALS AND ACCESSORIES

MATERIAL STANDARD
Accessories for gypsum veneer base ASTM C1047
Blended cement ASTM C595
Cold-formed steel studs and track, structural AISI S240
Cold-formed steel studs and track, nonstructural AISI S220
Exterior plaster bonding compounds ASTM C932
Hydraulic cement ASTM C1157; C1600
Gypsum casting and molding plaster ASTM C59
Gypsum Keene’s cement ASTM C61
Gypsum plaster ASTM C28
Gypsum veneer plaster ASTM C587
Interior bonding compounds, gypsum ASTM C631
Lime plasters ASTM C5; C206
Masonry cement ASTM C91
Metal lath ASTM C847
Plaster aggregates
Sand
Perlite
Vermiculite		 ASTM C35; C897
ASTM C35
ASTM C35
Plastic cement ASTM C1328
Portland cement ASTM C150
Steel screws ASTM C1002; C954
Welded wire lath ASTM C933
Woven wire plaster base ASTM C1032

2508.3 Single-ply application.

Edges and ends of gypsum board and gypsum panel products shall occur on the framing members, except those edges and ends that are perpendicular to the framing members. Edges and ends of gypsum board and gypsum panel products shall be in moderate contact except in concealed spaces where fire-resistance-rated construction, shear resistance or diaphragm action is not required.

2508.3.1 Floating angles. Fasteners at the top and bottom plates of vertical assemblies, or the edges and ends of horizontal assemblies perpendicular to supports, and at the wall line are permitted to be omitted except on shear resisting elements or fire-resistance-rated assemblies. Fasteners shall be applied in such a manner as not to fracture the face paper with the fastener head.

2508.4 Adhesives.

Gypsum board and gypsum panel products secured to framing with adhesives in ceiling assemblies shall be attached using an approved fastening schedule. Expandable foam adhesives for fastening gypsum wallboard shall conform to ASTM D6464. Other adhesives for the installation of gypsum wallboard shall conform to ASTM C557.

2508.5 Joint treatment.

Gypsum board and gypsum panel product fire-resistance-rated assemblies shall have joints and fasteners treated.

Exception: Joint and fastener treatment need not be provided where any of the following conditions occur:

  1. Where the gypsum board or the gypsum panel product is to receive a decorative finish such as wood paneling,

battens, acoustical finishes or any similar application that would be equivalent to joint treatment.

  1. On single-layer systems where joints occur over wood framing members.

  2. Square edge or tongue-and-groove edge gypsum board (V-edge), gypsum panel products, gypsum backing board or gypsum sheathing.

  3. On multilayer systems where the joints of adjacent layers are offset.

  4. Assemblies tested without joint treatment.

2508.6 Horizontal gypsum board or gypsum panel prod-uct diaphragm ceilings.

uct diaphragm ceilings. Gypsum board or gypsum panel products shall be permitted to be used on wood joists to create a horizontal diaphragm ceiling in accordance with Table 2508.6.

2508.6.1 Diaphragm proportions. The maximum allowable diaphragm proportions shall be 1 1 /2:1 between shear resisting elements. Rotation or cantilever conditions shall not be permitted.

2508.6.2 Installation. Gypsum board or gypsum panel products used in a horizontal diaphragm ceiling shall be installed perpendicular to ceiling framing members. End joints of adjacent courses of gypsum board shall not occur on the same joist.

25-6 2022 CALIFORNIA BUILDING CODE

Copyright © 2022 by, or licensed to, International Code Council, Inc. (ALL RIGHTS RESERVED); licensed to California Building Standards Commission pursuant to License Agreement. No further reproductions is authorized. Any unauthorized reproduction or distribution is a violation of the federal copyright act and the license agreement, and subject to civil and criminal penalties thereunder.

GYPSUM BOARD, GYPSUM PANEL PRODUCTS AND PLASTER

TABLE 2508.6 SHEAR CAPACITY FOR HORIZONTAL WOOD-FRAME GYPSUM BOARD DIAPHRAGM CEILING ASSEMBLIES

MATERIAL THICKNESS OF MATERIAL
(MINIMUM) (inches)		 SPACING OF FRAMING
MEMBERS (inches)		 SHEAR VALUEa, b
(PLF OF CEILING)		 MIMIMUM FASTENER SIZE
Gypsum board or gypsum
panel product		 1/2 16 o.c. 90 5d cooler or wallboard nail; 15/8-inch
long; 0.086-inch shank;15/64-inch headc
Gypsum board or gypsum
panel product		 1/2 24 o.c. 70 5d cooler or wallboard nail; 15/8-inch
long; 0.086-inch shank;15/64-inch headc

For SI: 1 inch = 25.4 mm, 1 pound per foot = 14.59 N/m. a. Values are not cumulative with other horizontal diaphragm values and are for short-term wind or seismic loading. Values shall be reduced 25 percent for

normal loading. b. Values shall be reduced 50 percent in Seismic Design Categories D, E and F. c. 1 1 /4-inch, No. 6 Type S or W screws are permitted to be substituted for the listed nails.

2508.6.3 Blocking of perimeter edges. Perimeter edges shall be blocked using a wood member not less than 2inch by 6-inch (51 mm by 152 mm) nominal dimension. Blocking material shall be installed flat over the top plate of the wall to provide a nailing surface not less than 2 inches (51 mm) in width for the attachment of the gypsum board or gypsum panel product.

2508.6.4 Fasteners. Fasteners used for the attachment of gypsum board or gypsum panel products to a horizontal diaphragm ceiling shall be as defined in Table 2508.6. Fasteners shall be spaced not more than 7 inches (178 mm) on center at all supports, including perimeter blocking, and not more than 3 /8 inch (9.5 mm) from the edges and ends of the gypsum board or gypsum panel product.

2508.6.5 Lateral force restrictions. Gypsum board or gypsum panel products shall not be used in diaphragm ceilings to resist lateral forces imposed by masonry or concrete construction.

2508.6.6 Diaphragm ceiling connection to partitions.

[DSA-SS & DSA-SS/CC and OSHPD 1, 1R, 2, 4 & 5] Gypsum board shall not be used in diaphragm ceilings to resist lateral forces imposed by partitions. Connection of diaphragm ceiling to the vertical lateral force resisting ele- ments shall be designed and detailed to transfer lateral forces.

Exception: [OSHPD 2] Single-story Type V skilled nursing or intermediate care facilities utilizing wood- frame or light-steel-frame construction.

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▸Contents — California Building Code (Title 24, Part 2)
California Building Code (Title 24, Part 2)
  1. Chapter 2 — DEFINITIONS AND ABBREVIATIONS
  2. Appendix G — FLOOD-RESISTANT
  3. Appendix L — EARTHQUAKE RECORDING
  4. Appendix M — TSUNAMI-GENERATED
  5. Appendix N — REPLICABLE
  6. Appendix O — PERFORMANCE-BASED
  7. Chapter 1 — SCOPE AND ADMINISTRATION
  8. Chapter 3 — OCCUPANCY CLASSIFICATION AND USE
  9. Chapter 4 — SPECIAL DETAILED REQUIREMENTS BASED ON OCCUPANCY A…
  10. Chapter 5 — GENERAL BUILDING HEIGHTS AND AREAS
  11. Chapter 6 — TYPES OF CONSTRUCTION
  12. Chapter 7 — FIRE AND SMOKE PROTECTION FEATURES
  13. Chapter 7A — MATERIALS AND CONSTRUCTION
  14. Chapter 8 — INTERIOR FINISHES
  15. Chapter 9 — FIRE PROTECTION AND LIFE SAFETY SYSTEMS
  16. Chapter 10 — MEANS OF EGRESS
  17. Chapter 11A — HOUSING ACCESSIBILITY
  18. Chapter 11B — ACCESSIBILITY TO PUBLIC BUILDINGS, PUBLIC ACCOMM…
  19. Chapter 12 — INTERIOR ENVIRONMENT
  20. Chapter 14 — EXTERIOR WALLS
  21. Chapter 15 — ROOF ASSEMBLIES AND ROOFTOP STRUCTURES
  22. Chapter 16 — STRUCTURAL DESIGN
  23. Chapter 16A — STRUCTURAL DESIGN
  24. Chapter 17 — SPECIAL INSPECTIONS AND TESTS
  25. Chapter 18 — SOILS AND FOUNDATIONS
  26. Chapter 19 — CONCRETE
  27. Chapter 20 — ALUMINUM
  28. Chapter 21 — MASONRY
  29. Chapter 22 — STEEL
  30. Chapter 23 — WOOD
  31. Chapter 24 — GLASS AND GLAZING
  32. ▸Chapter 25 — GYPSUM BOARD, GYPSUM PANEL PRODUCTS AND PLASTER
    Overview
    1. Section 2501
    2. Section 2502
    3. Section 2503
    4. Section 2504
    5. Section 2505
    6. Section 2506
    7. Section 2507
    8. Section 2508
    9. Section 2509
    10. Section 2510
    11. Section 2511
    12. Section 2512
    13. Section 2513
    14. Section 2514
  33. Chapter 26 — PLASTIC
  34. Chapter 27 — ELECTRICAL
  35. Chapter 28 — MECHANICAL SYSTEMS
  36. Chapter 30 — ELEVATORS AND CONVEYING SYSTEMS
  37. Chapter 31 — SPECIAL CONSTRUCTION
  38. Chapter 31B — PUBLIC POOLS
  39. Chapter 31C — RADIATION
  40. Chapter 31D — FOOD ESTABLISHMENTS
  41. Chapter 31F — MARINE OIL TERMINALS
  42. Chapter 32 — ENCROACHMENTS INTO THE PUBLIC RIGHT-OF-WAY
  43. Chapter 33 — SAFEGUARDS DURING CONSTRUCTION
  44. Chapter 35 — REFERENCED STANDARDS
  45. Appendix A — EMPLOYEE QUALIFICATIONS
  46. Appendix B — BOARD OF APPEALS
  47. Appendix C — GROUP U – AGRICULTURAL BUILDINGS
  48. Appendix D — FIRE DISTRICTS
  49. Appendix F — RODENTPROOFING
  50. Appendix H — SIGNS
  51. Appendix I — PATIO COVERS
  52. Appendix J — GRADING
  53. Appendix K — GROUP R-3 AND GROUP R-3.1 OCCUPANCIES
  54. Appendix P — EMERGENCY HOUSING

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