Occupancy Types in California: Groups, Mixed Use, and Changes

The occupancy types in the California Building Code are ten groups that sort every structure by how it is used: Assembly (A), Business (B), Educational (E), Factory and Industrial (F), High Hazard (H), Institutional (I), Mercantile (M), Residential (R), Storage (S), and Utility and Miscellaneous (U). Each group has subgroups tuned to specific risks, and the classification a building receives sets its allowable height and area, required fire-resistance ratings, sprinkler and alarm systems, and the number and arrangement of its exits.¹

How Occupancy Classification Works

The California Building Code (CBC) assigns classifications based on the hazards a building’s use presents to its occupants and neighbors. A hospital houses people who cannot evacuate on their own. A warehouse full of combustibles presents a fire-containment problem. A nightclub packs hundreds of people into a confined space. Different risks demand different construction standards, and occupancy classification is the mechanism that ties the right requirements to the right building.¹

The classification feeds into the CBC’s rules on construction type, maximum height and floor area, fire-protection systems, interior finishes, and egress. Two buildings identical in size and shape can face radically different code requirements when one is a restaurant and the other a hospital.

California adopts the International Building Code with state-specific amendments. The 2025 edition takes effect in 2026, replacing the 2022 edition. Most definitions carry over with minimal change, though California diverges from the model IBC in certain subgroups, most visibly in how it handles some assisted-living and care facilities.

Group A: Assembly

Assembly covers spaces where people gather for entertainment, worship, dining, recreation, or civic purposes. High occupant density is the defining risk. A room of people focused on a performance, unfamiliar with the exits, creates real evacuation challenges, so the code demands wider and more numerous exits, emergency lighting, and in many cases automatic sprinklers.

A-1: Performing arts and movie venues with fixed seating, including theaters, concert halls, and television studios with live audiences.
A-2: Food and drink establishments such as restaurants, banquet halls, bars, nightclubs, and casinos.
A-3: Worship, recreation, and general assembly uses that do not fit another A subgroup. Libraries, art galleries, courtrooms, community halls, bowling alleys, lecture halls, and places of worship all land here.
A-4: Indoor arenas and skating rinks where spectators watch sporting events from fixed seating.
A-5: Outdoor assembly venues like stadiums, grandstands, and outdoor bleacher seating.²

Group B: Business

Group B applies to offices, professional services, and similar workplaces. The list is broad: banks, medical and dental offices, law firms, dry cleaning pickup stations, post offices, print shops, motor vehicle showrooms, research laboratories, and educational facilities serving students above the 12th grade. The common thread is a relatively low fire load and occupants who are generally mobile and alert.²

Colleges and universities sit here rather than in Group E, which is worth flagging because it changes their egress and fire-protection obligations.

Group E: Educational

Group E covers buildings occupied by more than six children aged 36 months or older who receive educational, supervisory, or personal care services for fewer than 24 hours per day. K-12 schools, preschools, and larger licensed childcare centers fall here.³

Several carve-outs apply. A childcare facility with five or fewer children takes on whatever primary occupancy the building already holds rather than becoming Group E. A home-based daycare with five or fewer children falls under Group R-3. And if the facility serves children who cannot respond to an emergency without physical help from staff, it moves to Group I-4. The code caps a Group E childcare facility at five infants and toddlers before the institutional classification is triggered.³

Group F: Factory and Industrial

Group F covers facilities used for assembling, fabricating, manufacturing, packaging, or repairing products, provided the materials involved are not hazardous enough to trigger a High Hazard classification. The two subgroups split on combustibility:⁴

F-1 (Moderate Hazard): The default for industrial operations. If a factory does not qualify as F-2, it is F-1. Furniture manufacturing, woodworking shops, and facilities processing combustible materials are typical examples.
F-2 (Low Hazard): Facilities that fabricate or manufacture noncombustible materials where the finishing, packaging, or processing steps do not create a significant fire hazard. Metal stamping, glass production, and concrete product manufacturing fall here.

Group H: High Hazard

Group H is reserved for facilities that manufacture, process, or store materials posing a serious risk of fire, explosion, or health hazard in quantities that exceed what the code allows in a standard control area. A facility that stays under those maximum allowable quantities does not need an H classification; once they are exceeded, reclassification is required along with the substantial construction and fire-protection upgrades that come with it.⁵

The five subgroups escalate with the severity of the threat:

H-1: Materials that pose a detonation hazard, such as certain explosives. H-1 buildings must be set back at least 75 feet from property lines and other structures.
H-2: Materials that pose a deflagration hazard or an accelerated burning hazard, including flammable gases and certain combustible dusts.
H-3: Materials that readily support combustion or pose a physical hazard, such as flammable solids and oxidizers.
H-4: Health-hazard materials, including corrosives and highly toxic substances, without the fire or explosion risk of H-1 through H-3.
H-5: Semiconductor fabrication and similar operations that use hazardous production materials, with its own tailored requirements reflecting the safety systems these facilities already employ.

Group I: Institutional

Group I covers facilities where occupants cannot evacuate on their own, either because of medical conditions or because they are under security restraint. Code requirements reach their most demanding level here, since the building and its staff must compensate for what the occupants cannot do for themselves.⁶

I-2 (Medical Care): Hospitals, nursing homes, psychiatric hospitals, and detoxification facilities providing 24-hour medical care for more than five persons who are incapable of self-preservation. These buildings require the highest fire resistance, automatic suppression, and smoke compartmentalization.²
I-3 (Detention and Correctional): Jails, prisons, juvenile halls, detention centers, courtroom holding facilities, and reformatories. Occupants are generally incapable of self-preservation because security measures prevent free movement, and the code addresses this with specialized egress systems that staff can activate without compromising security.
I-4 (Day Care): Facilities providing supervisory care for more than five persons who cannot respond to emergencies without staff assistance, where the care lasts fewer than 24 hours. This covers certain childcare centers and adult day programs.

California does not use Group I-1. Facilities that would nationally fall under I-1, such as certain assisted-living homes with more than sixteen residents, are instead classified under the state’s R-2.1 designation, which applies residential-style requirements with added safety provisions rather than full institutional standards.²

Group M: Mercantile

Group M covers spaces where merchandise is displayed and sold to the public. Department stores, drug stores, retail and wholesale shops, markets, motor fuel-dispensing facilities, and greenhouses open to the public for plant sales all fall under M. The distinction from Group B matters because retail spaces tend to hold more combustible stock and draw higher concentrations of visitors, which pushes the code toward stricter fire-protection and egress requirements than a typical office building needs.⁷

Group R: Residential

Group R covers buildings where people sleep, whether for one night or permanently. The four active subgroups turn on how many units the building contains and whether the occupants are transient or long-term.

R-1 (Transient): Hotels, motels, and boarding houses with more than ten occupants who stay on a short-term basis. Because transient guests are unfamiliar with the layout, R-1 buildings face stricter fire alarm and emergency notification requirements than other residential types.
R-2 (Permanent, Multi-Unit): Apartment buildings, condominiums, dormitories, and similar structures containing more than two dwelling units where residents live on a permanent basis.²
R-3 (Permanent, Small): Single-family homes, duplexes, and buildings with no more than two dwelling units. Also covers small care facilities with six or fewer clients who stay for less than 24 hours.
R-4 (Supervised Residential Care): Facilities housing more than six but no more than sixteen ambulatory clients in a supervised 24-hour environment. Residents must be capable of self-preservation. Group homes and certain assisted-living facilities fall here.

Group S: Storage

Group S applies to buildings used primarily to store goods that are not classified as hazardous. Like Group F, it splits into two subgroups based on the combustibility of what is stored:⁸

S-1 (Moderate Hazard): Storage of combustible materials such as furniture, lumber, leather goods, clothing, tires, paper products, and self-service (mini-storage) facilities. Motor vehicle repair garages also fall here when they stay within hazardous material quantity limits.
S-2 (Low Hazard): Storage of noncombustible materials, including metals, glass, food products in noncombustible containers, cement, gypsum board, and empty cans. Public parking garages, both open and enclosed, are classified S-2.

Group U: Utility and Miscellaneous

Group U is the catch-all for accessory and miscellaneous structures that do not fit any other group. These are typically secondary structures on a property rather than primary buildings. The CBC lists agricultural buildings, barns, carports, private garages, sheds, livestock shelters, retaining walls, fences over 7 feet tall, grain silos accessory to a residence, and tanks and towers among the examples.⁹

Group U structures still must meet code requirements proportional to their fire and life-safety risk, but those requirements are far less demanding than what applies to occupied buildings. A detached residential garage, for instance, needs to meet fire-separation and setback rules without carrying the egress provisions of a commercial structure.

Mixed-Use Buildings

Most commercial buildings contain more than one type of use. A building with ground-floor retail, upper-floor apartments, and an underground parking garage involves at least three occupancy groups (M, R-2, and S-2). The CBC offers two main strategies for handling the overlap, plus a shortcut for small secondary uses.

Nonseparated Occupancies

Different occupancies coexist without fire-rated barriers between them, and the entire building must comply with the most restrictive requirements of any occupancy present. If one floor is R-2 and another is B, the whole building must meet whichever group demands greater fire resistance, more exits, and tighter sprinkler coverage. This approach tends to limit allowable building size because height and area follow the most restrictive occupancy. Even so, the code still requires fire-rated separation between dwelling or sleeping units in residential occupancies and between residential and adjacent non-residential spaces. Hazardous occupancies also must be separated regardless of the chosen strategy.

Separated Occupancies

The separated approach uses fire-rated walls and floor assemblies to divide different occupancy groups. Each portion then follows the rules for its own classification, and the required fire-resistance rating of the separating assemblies depends on which groups sit on either side. Ratings typically range from one to three hours, with lower ratings permitted when the building has a full automatic sprinkler system. Some occupancy pairings with similar hazard levels, such as B and F-1, require no separation at all.

Accessory Occupancies

A small use inside a larger building can qualify as an accessory occupancy if it does not exceed 10 percent of the floor area of the story where it sits. A gift shop inside a hotel lobby or a small office in a warehouse are common examples. Accessory occupancies still must be classified, but they follow a simplified compliance path that avoids the full separation requirements of the separated approach.¹⁰

Changing a Building’s Occupancy

Converting a building from one use to another, such as turning a warehouse into a restaurant, almost always triggers a change of occupancy under the CBC. A building changing to a more hazardous occupancy must be brought into compliance with the requirements for the new classification. That can mean structural upgrades, additional exits, new sprinkler systems, or upgraded fire-resistance ratings.¹¹

If the new use is less hazardous than the old one, the building official has discretion to allow the change without requiring full compliance with every provision for the new group. Converting a restaurant (A-2) to an office (B) moves to a lower-hazard classification, and the official may waive some upgrades.

When a change of occupancy pushes a building into a higher seismic risk category, the structure must also be evaluated against current earthquake standards. California’s seismic requirements are among the most demanding in the country, and this structural evaluation is often the most expensive part of a conversion project.¹¹

A new certificate of occupancy must be issued before the building can be used under its new classification. The building official verifies that the applicable requirements for the new occupancy have been met, typically through a combination of plan review and on-site inspections.

1
International Code Council. 2022 California Building Code, Title 24, Part 2 – Chapter 3 Occupancy Classification and Use
2
UpCodes. California Building Code 2022 – Chapter 3 Occupancy Classification and Use
3
UpCodes. Group E, Child-Care Facilities
4
UpCodes. California Fire Code 2022 – Group F, Factory Industrial
5
UpCodes. Group H, High-Hazard
6
CAL FIRE Office of the State Fire Marshal. I-3 Interpretive Digital Manual
7
UpCodes. Mercantile Group M
8
International Code Council. 2021 International Building Code – Chapter 3 Occupancy Classification and Use
9
UpCodes. California Building Code 2025 – Chapter 3 Occupancy Classification and Use
10
International Code Council. IBC Interpretation 27-12 – Accessory Occupancies Section 508.2
11
UpCodes. Section 3408A Change of Occupancy or Function