Skip to content

Chapter 5 — GENERAL BUILDING HEIGHTS AND AREAS

Section 509 — INCIDENTAL USES

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.

509.1 General Incidental uses located within single occupancy or mixed occupancy…

section. Incidental uses are ancillary functions associated with a given occupancy that generally pose a greater level of risk to that occupancy and are limited to those uses specified in Table 509.1.

Exception: Incidental uses within and serving a dwelling unit are not required to comply with this section.

�

[F] TABLE 509.1—INCIDENTAL USES

ROOM OR AREA SEPARATION AND/OR PROTECTION
Furnace room where any piece of equipment is over 400,000 Btu per
hour input		 1 hour or provide automatic sprinkler system
Rooms with boilers where the largest piece of equipment is over 15 psi
and 10 horsepower		 1 hour or provide automatic sprinkler system
Refrigerant machinery room 1 hour or provide automatic sprinkler system
Hydrogen fuel gas rooms, not classified as Group H 1 hour in Group B, F, M, S and U occupancies; 2 hours in Group A, E, I
and R occupancies.
Incinerator rooms 2 hours and provide automatic sprinkler system
Paint shops, not classified as Group H, located in occupancies other
than Group F		 2 hours; or 1 hour and provide automatic sprinkler system
In Group E occupancies, laboratories and vocational shops not classi-
fied as Group H		 1 hour or provide automatic sprinkler system
[SFM]Rooms or areas with special hazards such as laboratories, voca-
tional shops and other such areas not classified as Group H, located in
Group E occupancies where hazardous materials in quantities not
exceeding the maximum allowable quantity are used or stored.		 1 hour
In Group I-2 occupancies, laboratories not classified as Group H 1 hour_a_
In ambulatory care facilities, laboratories not classified as Group H 1 hour or provide automatic sprinkler system
Laundry rooms over 100 square feet 1 hour or provide automatic sprinkler system
In Group I-2, laundry rooms over 100 square feet 1 hour and provide automatic sprinkler system_a_
Group I-3 cells and Group I-2 patient rooms equipped with padded
surfaces		 1 hour and provide automatic sprinkler system_a_
In Group I-2, physical plant maintenance shops 1 hour and provide automatic sprinkler system_a_
In ambulatory care facilities or Group I-2 occupancies, waste and linen
collection rooms with containers that have an aggregate volume of
8.67 cubic feet or greater		 1 hour and provide automatic sprinkler system_a_
In other than ambulatory care facilities and Group I-2 occupancies,
waste and linen collection rooms over 100 square feet		 1 hour or provide automatic sprinkler system
In ambulatory care facilities or Group I-2 occupancies, storage rooms
greater than 50 square feet		 1 hour and provide automatic sprinkler system_a_
Electrical installations and transformers See Sections 110.26 through 110.34 and Sections 450.8 through 450.48
of the_California Electrical Code_for protection and separation
requirements.
For SI: 1 square foot = 0.0929 m2, 1 pound per square inch (psi) = 6.9 kPa, 1 British thermal unit (Btu) per hour = 0.293 watts, 1 horsepower = 746 watts, 1 gallon = 3.785 L,
1 cubic foot = 0.0283 m3.
a._ [SFM]_Fire barrier protection and automatic sprinkler protection required throughout the fire area in I-2 occupancies as indicated.

5-18 2025 CALIFORNIA BUILDING CODE

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

GENERAL BUILDING HEIGHTS AND AREAS

509.2 Occupancy classification.

Incidental uses shall not be individually classified in accordance with Section 302.1. Incidental uses shall be included in the building occupancies within which they are located.

509.3 Area limitations.

Incidental uses shall not occupy more than 10 percent of the building area of the story in which they are located.

Exception: Group E laboratories that are not classified as a Group H and are separated by a 1-hour fire barrier.

509.4 Separation and protection.

The incidental uses specified in Table 509.1 shall be separated from the remainder of the building or equipped with an automatic sprinkler system, or both, in accordance with the provisions of that table.

509.4.1 Separation. Where Table 509.1 specifies a fire-resistance-rated separation, the incidental uses shall be separated from the remainder of the building by a fire barrier constructed in accordance with Section 707 or a horizontal assembly constructed in accordance with Section 711, or both. Construction supporting 1-hour fire barriers or horizontal assemblies used for incidental use separations in buildings of Type IIB, IIIB and VB construction is not required to be fire-resistance rated unless required by other sections of this code.

509.4.1.1 Type IV-B and IV-C construction. Where Table 509.1 specifies a fire-resistance-rated separation, mass timber elements serving as fire barriers or horizontal assemblies in Type IV-B or IV-C construction shall be separated from the interior of the incidental use with an approved thermal barrier consisting of gypsum board that is not less than [1] / 2 inch (12.7 mm) in thickness or a material that is tested in accordance with and meets the acceptance criteria of both the Temperature Transmission Fire Test and the Integrity Fire Test of NFPA 275.

Exception: The thermal barrier shall not be required on the top of horizontal assemblies serving as incidental use separations.

509.4.2 Protection. Where Table 509.1 permits an automatic sprinkler system without a fire barrier, the incidental uses shall be separated from the remainder of the building by construction capable of resisting the passage of smoke. The walls shall extend from the top of the foundation or floor assembly below to the underside of the ceiling that is a component of a fire-resistancerated floor assembly or roof assembly above or to the underside of the floor or roof sheathing, deck or slab above. Doors shall be self- or automatic-closing upon detection of smoke in accordance with Section 716.2.6.6. Doors shall not have air transfer openings and shall not be undercut in excess of the clearance permitted in accordance with NFPA 80. Walls surrounding the incidental use shall not have air transfer openings unless provided with smoke dampers in accordance with Section 710.8.

509.4.2.1 Protection limitation. Where an automatic sprinkler system is provided in accordance with Table 509.1, only the space occupied by the incidental use need be equipped with such a system.

Get a plain-English answer with a citation back to this text.

Ask AI about this code
▸ 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
    Overview
    1. Section 501 — GENERAL
    2. Section 502 — BUILDING ADDRESS
    3. Section 503 — GENERAL BUILDING HEIGHT AND AREA LIMITATIONS
    4. Section 504 — BUILDING HEIGHT AND NUMBER OF STORIES
    5. Section 505 — MEZZANINES AND EQUIPMENT PLATFORMS
    6. Section 506 — BUILDING AREA
    7. Section 507 — UNLIMITED AREA BUILDINGS
    8. Section 508 — MIXED USE AND OCCUPANCY
    9. Section 509 — INCIDENTAL USES
    10. Section 510 — SPECIAL PROVISIONS
  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
  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

GoCodebook provides public access, search, citation, multilingual explanation, and practical interpretation of legally adopted building regulations. It is not a substitute for the official ICC or California code publications.