2021 IBC Chapter 3
Almost every other requirement in the IBC starts with a question from this lesson: what is the building used for? Occupancy group sets how far people may travel to an exit, whether sprinklers are required, how much area the building may have, and how walls and floors must be rated. Chapter 3 sorts every use into one of ten groups, A, B, E, F, H, I, M, R, S, and U, and each group has short tests that separate it from its neighbors. This lesson walks through those tests. The rules for a building that holds several groups come in Lesson 3.
Section 302.1 requires each building or portion of a building to be classified by its use into one or more of the groups in Sections 303 through 312. You classify the use, not the building's shape or age. Where a building holds more than one use, each portion gets its own classification, and Lesson 3 covers how they combine. Two ideas appear here only as previews: a small room that serves another use (an accessory room, such as a conference room in an office) may join that use instead of becoming its own group, and support spaces such as boiler rooms are handled by the incidental use rules of Section 509.
Group A covers gathering for civic, social, or religious functions, recreation, food and drink, or waiting for transportation. The five subgroups are split by what people do. A-1 is watching performing arts or motion pictures, usually with fixed seating (theaters, concert halls, broadcast studios with an audience). A-2 is food and drink: restaurants, taverns, bars, nightclubs, banquet halls, and casino gaming areas. A-3 is worship, recreation, and other assembly not listed elsewhere: places of worship, libraries, museums, community halls, lecture halls, courtrooms, gyms and pools without spectator seating. A-4 is viewing indoor sports with spectator seating, so the same pool or gym is A-3 without bleachers and A-4 with them. A-5 is outdoor activity, such as stadiums and grandstands.
Small assembly uses drop out of Group A. A building or tenant space used for assembly with an occupant load of fewer than 50 people is Group B (303.1.1). A room that is accessory to another occupancy is not Assembly if its occupant load is under 50 or its area is under 750 sq ft (303.1.2). Both tests apply only to the situations they describe: the 750 sq ft test is for accessory rooms, not for whole tenant spaces. An assembly space that goes with a Group E building is not a separate occupancy (303.1.3), and accessory religious education rooms and religious auditoriums under 100 people per room are not separate occupancies either (303.1.4).
Group B is office, professional, or service-type transactions, including storage of records. The list is broader than most people expect: banks, barber and beauty shops, civic administration, outpatient clinics and ambulatory care, animal hospitals, dry cleaning pick-up, self-service laundries, laboratories, motor vehicle showrooms, post offices, print shops, and educational use above the 12th grade. Ambulatory care is care on a less than 24-hour basis to people who are, or are made by the care, incapable of self-preservation; it is Group B with extra rules. Group E is educational use by six or more people at a time through the 12th grade, and day care for more than five children older than 2-1/2 for fewer than 24 hours a day (305.1, 305.2). Day care within a place of religious worship, or for five or fewer children, is part of the primary occupancy (305.2.1, 305.2.2), and five or fewer in a dwelling unit is R-3 or falls under the IRC (305.2.3).
Group F is assembling, fabricating, finishing, manufacturing, packaging, or processing that is not H or S. F-1 is the moderate-hazard default: anything not F-2, including furniture, cabinet woodworking, clothing, electronics, printing, laundries, and beverages over 16 percent alcohol. F-2 is low hazard, noncombustible work such as brick and masonry, and beverages of 16 percent alcohol or less. Group S is storage that is not hazardous. S-1 is moderate hazard: furniture, bulk cardboard and tires, clothing, self-service storage, and repair garages within the hazardous material limits. S-2 is low hazard: food products, glass, metals, and public parking garages, whether open or enclosed (311.3). A storage room accessory to another occupancy is part of that occupancy (311.1.1). Group U is the catch-all for accessory and miscellaneous structures: private garages, carports, sheds, barns, stables, tanks, towers, retaining walls, and fences over 7 ft (312).
Group H covers making, using, or storing materials with a physical or health hazard above the maximum allowable quantities in Tables 307.1(1) and 307.1(2), counted per control area. Below the limits the use stays in its ordinary group, so a small retail shop with a shelf of solvents is still Group M. H-1 is a detonation hazard (explosives). H-2 is deflagration or accelerated burning (combustible dusts, flammable liquids in open containers). H-3 is materials that readily support combustion or pose other physical hazards (flammable solids, some oxidizers). H-4 is health hazards (corrosives and toxics). H-5 is semiconductor fabrication and comparable research. Where several hazards are present, the space must meet each classification (307.8). Group H is rare in GCHS work, but you must be able to tell when quantities push a use into it.
Group I is care, supervision, or detention of people who cannot get out on their own or are held. I-1 houses more than 16 people, not counting staff, in a supervised 24-hour custodial environment: assisted living, group homes, halfway houses. Condition 1 means all can respond without help; Condition 2 means some need limited assistance. I-2 is 24-hour medical care for more than five people incapable of self-preservation: nursing homes (Condition 1, no emergency care or surgery) and hospitals (Condition 2). I-3 holds more than five people under restraint or security, in Conditions 1 to 5 by how freely they move. I-4 is custodial care for more than five people of any age for less than 24 hours a day away from home: adult day care and, for young children, some child day care (308.5). The counts matter at the low end. The same 24-hour supervised residence is I-1 for more than 16, R-4 for 6 to 16, and R-3 (or the IRC with sprinklers) for five or fewer.
Group M is display and sale of merchandise where the public has access: department stores, drug stores, markets, retail and wholesale stores, and motor fuel-dispensing facilities. A warehouse with no public access is S, not M. Group R is sleeping when it is not Group I and not covered by the IRC. R-1 is primarily transient: hotels, motels, and boarding houses or congregate living with more than 10 occupants. R-2 is permanent residence in sleeping units or in buildings with more than two dwelling units: apartments, dormitories, convents, nontransient hotels, and live/work units. R-3 is permanent residence not in R-1, R-2, R-4, or I: buildings with not more than two dwelling units, care of five or fewer people, and small lodging houses. R-4 is the 6 to 16 person supervised residence, built like R-3 except where the code says otherwise. Group R not built to the IRC also answers to Section 420, covered in Lesson 3.
Worked example. Classify these five tenant spaces using only the tests above. (a) A fitness studio with a design occupant load of 40: Group B, since assembly under 50 people is B. (b) The same studio after a change to a load of 60: Group A-3, since it is no longer under 50. (c) A 700 sq ft conference room with 80 seats inside a 12,000 sq ft office: it is accessory and under 750 sq ft, so it stays part of Group B. (d) An 800 sq ft training room with a load of 60 in the same office: over 750 sq ft and over 50 people, so it is A-3. (e) A commissary kitchen of 3,200 sq ft that supplies caterers and is not part of a restaurant: over 2,500 sq ft, so F-1. Notice that (b) and (d) change the required fire protection, which is why the occupant load appears on the certificate of occupancy.
In the field
A GCHS client wants to convert a large house into a home for eight seniors who need 24-hour supervision and help with daily living. Do not start with the floor plan; start with the count and the care. Eight residents with custodial care in a supervised residence puts it in Group R-4 (more than five, not more than 16), built like R-3 with extra provisions. If the plan grows past 16 residents, it becomes I-1 and the requirements change sharply. If it drops to five, it is R-3 or the IRC with sprinklers. Ask early which count the client intends, and whether residents can respond to an alarm on their own, because that sets Condition 1 or 2.
1. A physical therapy studio leases a tenant space where classes of up to 40 people gather at one time. Under Section 303.1.1, the space is classified as:
2. A neighborhood restaurant with a design occupant load of 90 serves food and drink. It is classified as:
3. A nonprofit thrift store sells donated goods to the public in a 6,000 sq ft sales room. The use is classified as:
4. A city recreation center has an indoor swimming pool with bleachers for spectators at swim meets. The pool area is classified as:
5. In a Group B office building, an accessory training room measures 800 sq ft and has an occupant load of 60. Under Section 303.1.2, the training room is:
6. A clinic provides same-day care to patients made incapable of self-preservation by the services, and no patient stays overnight. The clinic is classified as:
7. A commissary kitchen prepares food for caterers, is not associated with a restaurant, and covers 3,200 sq ft. Its classification is:
8. A tutoring center serves eight middle-school students at one time. Under Section 305.1, the center is classified as:
9. A stand-alone child day care center cares for 20 children between ages 3 and 5, for fewer than 24 hours a day. Under Section 305.2, the classification is:
10. A shop assembles cabinets from lumber and sheet goods and sells only to contractors, with no public sales floor. Which group fits?
11. A new building holds rentable self-service storage units. Which group applies?
12. A supervised residence houses 12 residents who receive custodial care 24 hours a day, plus staff. Under Section 310.5, the group is:
13. An assisted living facility houses 24 residents, excluding staff, in a supervised 24-hour environment with custodial care. Under Section 308.2, the group is:
14. A new building has eight apartments rented to permanent residents. It is classified as: