Classification of Buildings and Occupancies by Fire Hazard (OBC Part 3)
Major occupancies
The Code classifies buildings by major occupancy groups, from Group A (assembly) through Group B (care or detention), Group C (residential), Group D (business and personal services), Group E (mercantile), and Group F (industrial, divided into F1 high hazard and F2 medium hazard). Each group carries subdivisions, such as A1 through A4, reflecting occupant load and conditions of egress.
Building height and area
Classification drives the permitted building height and area, which depend on construction type, sprinkler protection, and occupancy. Combustible versus noncombustible construction is a separate but linked concept. The most restrictive occupancy in a building generally governs, and a building may be classified by more than one major occupancy.
Traps
- Treating F1 and F2 as interchangeable; F1 is the higher hazard and attracts stricter limits.
- Forgetting that sprinkler protection can relax height and area limits.
- Missing that a building can hold multiple major occupancies with different requirements.
- Confusing occupancy classification with construction type or with fire-resistance ratings.
- Assuming occupant load alone determines the group; use of the space matters.
Rule of thumb
Classify by the hazard of the activity, not the name of the tenant. A worked example: a two-storey building with a repair garage on the ground floor and offices above is not simply Group D. The garage may be Group F2 and the offices Group D, so the more restrictive requirements for the F2 occupancy apply to the shared building elements, and the separation between occupancies must be checked.
Exam approach
Read the scenario for storage quantities, occupant loads, and whether occupants are asleep, awake, restrained, or in a high-hazard process. Those cues point to the group.