Building Planning and Occupancy Classification
Building Planning and Occupancy Classification
This domain tests occupancy classification, mixed and accessory occupancies, incidental uses, and the planning limits that follow from classification: allowable height, allowable area, frontage increases, and sprinkler credits.
Core rules
- Every building or space is classified into an occupancy group: A (assembly), B (business), E (educational), F (factory), H (high-hazard), I (institutional), M (mercantile), R (residential), S (storage), or U (utility).
- Assembly occupancies are subdivided by occupant load and use: A-1 through A-5. A restaurant with concentrated seating is typically A-2; a community hall may be A-3.
- Accessory occupancies are permitted under Section 508.2 only when the space is subordinate and limited in area, generally not more than 10 percent of the story’s floor area, and not high-hazard.
- Mixed occupancies use either the separated method, with fire-resistance separations from Table 508.4, or the nonseparated method, where each story must satisfy the most restrictive height and area limits.
- Incidental uses under Section 509 are subordinate uses that require separation from the primary occupancy, such as a furnace room or hazardous storage.
Worked example
A 12,000-square-foot single-story building contains 3,000 square feet of restaurant seating (A-2) and 9,000 square feet of offices (B). The restaurant is 25 percent of the floor area, far above the accessory-occupancy limit. It cannot be treated as an accessory use. The designer must classify the building as a mixed occupancy and choose either the separated method, providing the required fire separation between A-2 and B, or the nonseparated method, where the story must comply with the most restrictive height and area requirements. Sprinkler and frontage increases must be verified against the applicable tables.
Traps
- Misclassifying A-2 restaurant space as A-3 or as an accessory use.
- Using accessory-occupancy rules when the 10 percent limit is exceeded.
- Forgetting that incidental uses require separation even though they are not separate occupancies.
- Applying area increases for sprinklers or frontage without confirming eligibility.