Codes & Regulations: Occupancy, Egress, and Accessibility Logic
Codes questions reward precision about definitions and punish shortcut assumptions.
Occupancy and construction. Every building gets an occupancy group (A, B, E, F, H, I, M, R, S, U) and a construction type from I through V, with A and B subtypes where A is more fire resistive. The allowable height and area tables combine these two inputs, then adjust for sprinklers, frontage, and separation. Trap: adding the sprinkler increase when the building lacks a compliant system throughout.
The egress chain. Exit access, exit, and exit discharge are separate components with separate rules. Occupant load = floor area ÷ the tabulated load factor, and the basis matters: business uses a gross 150 sf per occupant, classrooms a net 20, unconcentrated assembly a net 15. Mixing gross and net is among the most common errors.
Capacity and geometry. Egress width is 0.2 in per occupant on level components and 0.15 in on stairs, with corridor minimums of 36 in that override the math at low loads. Two exits are required once the occupant load passes the single-exit threshold. Dead ends, common path, and travel distance are three separate limits - do not swap them.
Accessibility. Ramps max out at 1:12 with 30 in of rise per run, doors need 32 in clear width, and turning clearances at doors are frequently tested.
Worked example: a 10,000 sf business floor yields 10,000 ÷ 150 ≈ 67 occupants. That exceeds the single-exit limit, so two exits are required; calculated width is 67 × 0.2 = 13.4 in, so the 36-in corridor minimum governs instead.