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Occupancy Group Classification

One of the first tasks an architect is to do when determining the code requirements is to establish the occupancy group of a space. A building may have a single occupancy group if it has a singular purpose, provided that the ancillary space spaces, such as conference rooms and break rooms, fall within the provisions of accessory occupancies. Typically, many modern buildings have multiple occupancy groups. This could include an office space with a large assembly space for employee training, a mixed-use podium building with retail and parking below residential and amenity spaces above a concrete deck or even a more complicated structure such as a hospital which may have many occupancy groups within the structure.

Purpose of the Space

The first place to start in determining the occupancy group is to think about the “purpose” of the building or space.Section 302.1 states that the occupancy group is a formal designation of the purpose of a building. The dictionary defines “purpose” as the reason for which something is done or created or for which something exists. How would the space, building or structure be described in a few words, if you were to stop people on the street and poll them? A high school isn’t “an educational institution for 9-12 grade” to most people, if you were to ask them… it’s called a “high school”, or just simply “school”, and most people understand what that entails. The purpose of a building is to be a “school”. The school board sells bonds for the purpose of constructing a “school”. Education (the verb and noun) is what we all hope happens within.

However, the requirement to establish an occupancy group applies to the individual spaces that make up the building. Even though there may be a “School”, it likely also has a gymnasium and perhaps a cafeteria or everyone’s favorite: the “Cafetorium”. Each of these spaces should be analyzed separately with it’s own occupancy group provided. Multipurpose spaces such as our ‘cafetorium’ are required to be analyzed for the most restrictive requirements of each. In code terms, it must “comply with all applicable requirements…”.

Other buildings may have multiple “purposes”, such as a car dealership. These buildings have both areas for car sales and typically a repair garage adjacent or part of the same building.

Basic Occupancy Group Descriptions / ExamplesOccupancy Group
Assembly — Theaters, churches, restaurantsA
Business — office buildings, doctor’s offices, tutoringB
Educational — elementary, middle and high schoolsE
Factory Industrial — low and moderate hazards production or fabricationF
High Hazard — processes, manufacturing or storage involving hazardous materials and/or chemicalsH
Institutional — facilities that provide care or supervision limiting movement or ability to respond to an emergency, such as day care, hospitals or jailsI
Mercantile — grocery, general merchandise and other goodsM
Residential — hotels, apartments, housesR
Utility and Miscellaneous — barns, sheds and garagesU

Selection of Occupancy Groups

To select the proper occupancy group, first understand the use and how the user intends and plans to use the spaces involved. Properly understanding the needs of the client at the beginning will help understand the use of the space in question. While it’s unlikely to confuse a conference room with a hazardous materials storage room, confusion may occur in determining exactly which occupancy group is most appropriate. Is a nursing home an I-1, I-2, R-4 or something else? Unless we work doing the same project time often, we likely won’t remember the variations between an E, an I-4 or an R-3 day care facility. Some of these occupancy groups are based on the occupant load or maybe the number of people served. A larger conference room may be an A-3, while a slightly smaller conference room is required to be a B occupancy in some states, and may optionally be a B occupancy in other states. To correctly apply the correct occupancy group requires sitting down with the code and properly analyzing the building and it’s individual spaces.

Another tool available is the UpCodes Occupancy Guide. This tool guides you through a series of questions to help you find the occupancy group, and to inform the user as to why it is a particular occupancy group.

State Specific Occupancy Groups

Not only can various occupancy groups be confusing, another layer of state regulations and building code amendments in some states can become more confounding. Some states such as California, have added a number of occupancy groups to address specific state requirements promulgated by various agencies. These include deletion of I-1, addition of I-2.1, R-2.1, R-2.2 and R-3.1. In addition, various thresholds for uses such as day-cares can be adjusted to meet state licensing requirements. Here again, the Occupancy Guide by UpCodes can provide direction in deciding which occupancy group is most appropriate.

Occupancy Classifications: Past and Present

Before we had the more commonly known occupancy group designations of A, B, E, I etc., the occupancy designations were labeled A - J with relative risk based on occupancy ranked from highest (A) to lowest (J). While this gives a general idea of risk to large numbers of occupants, it was not descriptive and did not rank hazardous facilities with a high level of risk. It becomes problematic when a change of occupancy is proposed to a building that was originally permitted under these old occupancy groups. If the original permit or certificate of occupancy stated a B-2, that would not therefore be a Group B occupancy under the current code, but likely an A-3 occupancy.

Occupancy Group Description per 1973 UBC1973 UBC Occupancy GroupApproximate 2018 Code Occupancy Group
Assembly with stage and >= 1000 in the buildingALikely A-1
Assembly with stage and < 1000 in the buildingB-1Likely A-1
Assembly without stage and OL >= 300 and not C or F-2 occupancyB-2A-3
Assembly without stage OL < 300 and not C or F-2 occupancyB-3A-3
Stadiums, reviewing stands and amusement park structures Not Group A, B-1, B-2 or B-3B-4A-5, possible A-4
Any building used for educational purposes through the 12th grade by 50 or more persons for more than 12 hours per week or four hours in any one day.C-1E
Any building used for educational purposes through the 12th grade by less than 50 persons for more than 12 hours per week of four hours in any one day.C-2E
Any building used for day care purposes for more than 6 children.C-3I-4
Mental hospitals, jails or where personal liberties are similarly restrainedD-1I-2 (psychiatric hospitals); I-3 (jails)
Nurseries for full time care of children under kindergarten, hospitals, and nursing homes with non-ambulatory patientsD-2I-2
Nursing homes (ambulatory), homes for children kindergarten age and olderD-3I-1
Storage and handling of highly inflammable or explosives other than flammable liquidsE-1H-1*
Storage and handling of Class I, II or II flammables, etc.E-2H-2*
Woodworking establishments, planing mills, box factories and other locations where loose combustible fibers are generated, etc.E-3F-1, possibly H-3*
Repair GaragesE-4S-1
Aircraft repair hangersE-5S-1
Gasoline service stations, storage garages and maintenance garagesF-1M, S-1
Wholesale and retail stores, office buildings, restaurants with OL < 100, municipal police and fire stations, factories and workshops using material not highly flammable or hazardous, storage, paint stores, etc. Educational purposes beyond 12th grade with OL < 50.F-2B, M, F-1, S-1, H-4**, H-5**
Aircraft hangers, other than repair hangers; Open parking garagesF-3S-2
Ice plants, power plants, creameries, factories, workshops or storage using noncombustible and nonexplosive materials, etc.GF-1 (power plants); F-2
Hotels and apartment housesHR-1; R-2
Single Family HomeIR-3
Sheds, barns, carportsJU

* Always consult with a hazardous materials specialist or fire protection engineer when considering occupancies related to hazardous materials.
** H-4 and H-5 consider toxic materials and materials related to semiconductor fabrication, and do not have a direct correlation with the 1973 building code.
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Please note we’ve used the Wyoming Building Code for the examples above as it shares much in common with many other state and city codes. Please reference your jurisdiction’s codes for amendments specific to your project.