Occupancy Classification
The IBC's way of sorting buildings by how people use them.
Quick Answer
Occupancy classification is the IBC process of assigning a building or space to a use group based on its purpose and hazard. The main groups are Assembly (A), Business (B), Educational (E), Factory (F), High-Hazard (H), Institutional (I), Mercantile (M), Residential (R), Storage (S), and Utility (U). The group drives many other code requirements.
The Full Picture
Occupancy classification is the first code decision on most projects because so many other requirements key off it. The IBC groups buildings by use and by the level of risk that use creates, such as how many people gather, whether occupants can self-evacuate, and what hazardous materials are present. The classification is set out in IBC Chapter 3.
The ten main groups are Assembly (A), Business (B), Educational (E), Factory (F), High-Hazard (H), Institutional (I), Mercantile (M), Residential (R), Storage (S), and Utility and Miscellaneous (U). Several are divided into subgroups. For example, Assembly includes A-1 through A-5 and Residential includes R-1 through R-4, each with different thresholds and requirements.
Once the use group is set, it feeds allowable building height and area, required construction type, fire-resistance ratings, sprinkler and alarm requirements, occupant load, egress design, and plumbing fixture counts. A change in classification can therefore change the whole code analysis, which is why a tenant change from office to restaurant is not a trivial permit.
Buildings often contain more than one use. The IBC lets a designer treat the building as mixed occupancy, applying separation requirements between uses, or in some cases treat the whole building under the most restrictive use. Choosing between those approaches is a design decision with cost consequences, and the code official ultimately accepts or rejects the classification.
Real Examples
Common Misconceptions
People assume: Occupancy classification and zoning use are the same thing.
Actually: Zoning regulates land use under local planning law. Occupancy classification is a building code concept that governs life safety and construction. A use can be permitted by zoning and still require a different code classification.
People assume: A building has just one occupancy group.
Actually: Many buildings are mixed occupancy, with different groups in different areas, and the code requires separations or the most restrictive treatment for the combined building.
Does MeltPlan Solve This?
Yes — direct fitOccupancy analysis is a code research task, which is what MeltPlan Code supports. It helps teams look up the relevant IBC use group provisions and see how a classification affects other requirements. The final classification still belongs to the design professional and is subject to the code official's acceptance.
Check occupancy requirements in the code →Frequently Asked Questions
What are the IBC occupancy groups?
Assembly (A), Business (B), Educational (E), Factory (F), High-Hazard (H), Institutional (I), Mercantile (M), Residential (R), Storage (S), and Utility and Miscellaneous (U), with subgroups for several of them.
Where is occupancy classification in the IBC?
It is covered in Chapter 3, Use and Occupancy Classification. Chapter 5 and Chapter 6 then use the classification to set height, area, and construction type limits.
What is a mixed-occupancy building?
It is a building with more than one use group. The IBC lets designers either separate the uses with fire-rated construction or apply the most restrictive requirements to the whole building, depending on the approach chosen.
Who decides a building's occupancy classification?
The design professional proposes it based on the intended use, and the building official reviews and accepts it during plan review. If the use changes later, the classification may need to be revisited.