Building: Occupancy, Egress, and Fire-Resistance Essentials
Start with occupancy and construction type
Every building question begins with two identifiers: the occupancy classification (what the space is used for) and the construction type (how fire-resistive the structure is). Occupancy drives allowable area and height; construction type sets how much fire resistance the structural frame, bearing walls, and floor assemblies must provide. A common trap is answering an area question using the wrong occupancy group because a mixed-use building contains a small accessory space. Accessory occupancies are classified by the main use unless they exceed the code's accessory threshold.
Egress is a chain, not a single number
Understand the three parts of means of egress: exit access (the path from the room to the exit), the exit itself (stairs, ramps, exit passageways), and exit discharge (the path from the exit to the public way). Questions often give a travel distance that looks compliant but hide a dead-end corridor or a single-exit condition. Check occupant load first, then required egress width, then the number of exits. Remember that occupant load factors are area per person, so dividing floor area by the factor gives occupants, and that number sets width and exit count.
Fire-resistance and opening protection
Know how hourly ratings apply to assemblies and how openings (doors, windows, ducts) are protected. A frequent trap: a rated wall is only as good as its penetrations. Also distinguish between a fire partition, a fire barrier, and a fire wall; each has different continuity and support requirements.
Worked rule of thumb
For a 6,000 sq ft assembly space with an occupant load factor of 15 sq ft per person: 6,000 / 15 = 400 occupants. At 0.2 inches per occupant for level components, that is 80 inches of clear width, and the exit count must satisfy the code threshold for that occupant load. Always show the division before choosing an answer.