Occupancy Classification and Construction Types
Classifying occupancy
- Every space is assigned a group: assembly, business, educational, factory/industrial, high-hazard (H-1 through H-5), institutional, mercantile, residential, storage, or utility.
- Classification drives egress, fire protection, and allowable construction - so classify each space first, then decide whether occupancies are separated or non-separated.
- Incidental uses (a furnace room, a small storage room) may be classified separately inside a main occupancy when they stay within the incidental-use limits.
- Accessory occupancies are subordinate in area and function; exceed the limit and the space becomes a principal occupancy.
Construction types
- Types I through V, each in protected (A) and unprotected (B) form. Type I-A is the most fire-resistive; Type V-B is combustible and the least restrictive.
- Height and area limits come from tables keyed to construction type and occupancy, then adjusted for sprinklers and open frontage.
- Unlimited-area provisions exist only for specific occupancy and type combinations, usually requiring sprinklers and perimeter access.
Worked example
A repair garage stores 40 gallons of flammable liquid in an unseparated room. If that quantity exceeds the control-area or incidental-use threshold, the storage can drive a High-Hazard classification for the room rather than remaining a minor storage accessory. That reclassification changes required separations, sprinkler design, and the building's allowable height and area - and H occupancies frequently cannot use the standard area increases.
Traps
- Applying both a sprinkler increase and a frontage increase without checking whether the table permits stacking.
- Calling a space "accessory" when it exceeds the area or hazard limits.
- Forgetting that a change of occupancy can trigger compliance with the new group's requirements.