Section 302.1/Occupancy Classification
IBC 302.1 requires every building to be classified by occupancy, which drives nearly every other code requirement.
Every building or portion of a building must be individually classified according to its use or occupancy. The IBC defines ten occupancy groups: Assembly (A-1 through A-5), Business (B), Educational (E), Factory (F-1, F-2), High Hazard (H-1 through H-5), Institutional (I-1 through I-4), Mercantile (M), Residential (R-1 through R-4), Storage (S-1, S-2), and Utility (U). Where a building contains multiple uses, the requirements for mixed occupancy in Section 508 apply.
Why this section exists
The occupancy classification is the foundation of the entire IBC analysis. It determines the allowable height and area (Chapter 5), construction type (Chapter 6), fire protection requirements (Chapter 9), means of egress design (Chapter 10), interior finish (Chapter 8), and plumbing fixture counts (IPC). A wrong occupancy classification invalidates every downstream decision. This is always the first item a plan reviewer checks.
What plan reviewers look for
Plan reviewers verify the occupancy classification stated on the cover sheet and in the code analysis against the actual use described in the architectural program. They check for mixed occupancy conditions (accessory uses, separated uses, or nonseparated uses per Section 508). They verify that each occupancy group's specific requirements are addressed in the design.
Common violations
Related IBC requirements
Section 508 covers mixed occupancy requirements. Chapter 5 uses the occupancy to determine allowable height and area. Section 903.2 uses the occupancy to determine sprinkler requirements. Section 1004.1uses the occupancy to determine the occupant load.