Egress Calculation Is a Multi-Step Process - Start With Occupant Load, Then Work Through Number of Exits, Width, and Travel Distance
Calculating egress requirements for a building floor plate is one of the most fundamental code compliance skills in architectural practice, and it is reliably tested on the ARE PA exam. The IBC egress calculation process has a defined sequence: determine occupant load → determine minimum number of exits → calculate required exit width → verify that travel distance and common path of travel comply with the maximum limits for the occupancy type → design the egress path layout to comply with all of these requirements simultaneously. Working through this sequence systematically - rather than jumping to travel distance without confirming occupant load - produces a correct and defensible egress design. The following is the complete egress calculation methodology as required by the IBC.
Step 1: Determine Occupant Load
Occupant load = floor area (sq ft) ÷ occupant load factor (sq ft per person). IBC Table 1004.5 provides occupant load factors by occupancy and function: business areas (offices, conference rooms): 150 SF/person gross; retail: 60 SF/person gross; assembly without fixed seating (restaurant dining): 15 SF/person net; assembly with fixed seating: actual number of seats; classroom: 20 SF/person net; warehouse: 500 SF/person gross. Example: 6,000 SF office floor, business use: 6,000 ÷ 150 = 40 occupants.
Step 2: Number of Exits
IBC Section 1006 establishes minimum exit count by occupant load: Occupant load 1-49: 1 exit (with exceptions for multistory requirements). Occupant load 50-499: 2 exits minimum. Occupant load 500-999: 3 exits minimum. Occupant load 1,000+: 4 exits minimum. Example: 40-person office floor → 1 exit minimum. But be careful: 1 exit from a floor serving multiple stories typically requires additional analysis; most multi-story office buildings require 2 exits from each floor for practical reasons. Additionally, if there is only 1 exit, the travel distance limit is reduced (typically 75 ft maximum in sprinklered office; 100 ft in unsprinklered).
Step 3: Exit Width
Required exit width = occupant load × 0.2 inches per occupant for stairs; 0.15 inches per occupant for level egress components (corridors, doors), per IBC Section 1005. Minimum door width: 32 inches (required by ADA); minimum corridor width: 44 inches (IBC Section 1020). For our 40-person office: doors: 40 × 0.15 = 6 inches → controlled by 32-inch ADA minimum. Stairs: 40 × 0.2 = 8 inches → controlled by 44-inch code minimum. In practice, minimum widths always control for small occupant loads; capacity calculations become constraining for large occupant loads (above ~200 persons for typical stairs).
Step 4: Travel Distance
Travel distance is the distance from the most remote occupied point in a room to the nearest exit (measured along the actual path of travel, not as a straight line). IBC Table 1017.2 by occupancy and sprinkler status: Business (A, B, M, S) with NFPA 13 sprinkler: 300 ft; without sprinkler: 200 ft. Assembly (A) with sprinkler: 250 ft; without: 200 ft. High-hazard (H-1): 75 ft (sprinklered or not). Example: in our sprinklered office building, travel distance of 300 ft maximum - this is very generous and rarely controls for typical office floors.
Step 5: Common Path of Travel
Common path of travel (CPOT) is the portion of the egress path that must be traversed before reaching a point from which two separate exits are accessible. IBC Section 1006.2.1: maximum CPOT varies by occupancy. In B occupancies (office): 100 ft CPOT with sprinkler, 75 ft without. CPOT is often the constraining element in floor plans with a central exit cluster - occupants at the far end of the floor may need to walk the entire length to reach the first point where they have two exit choices, exceeding the CPOT limit and requiring a second exit at the far end of the floor.
Key Exam Points
- Occupant load: floor area ÷ occupant load factor (IBC Table 1004.5). Office: 150 SF/person gross.
- Number of exits: 50+ occupants = 2 exits; 500+ = 3; 1,000+ = 4 (IBC Table 1006.3.3).
- Exit width: 0.2 in/occupant (stairs); 0.15 in/occupant (corridors/doors); ADA and code minimums often govern.
- Travel distance: sprinklered office: 300 ft; unsprinklered: 200 ft (IBC Table 1017.2).
- Common path of travel: often the controlling factor in floor plan layout; 75-100 ft max (occupancy dependent).
AREprep's PA code analysis content covers the complete egress calculation sequence - occupant load, exit count, exit width, travel distance, and common path of travel - with practice problems that mirror the PA exam's building code application questions, giving ARE PA candidates the systematic code compliance methodology they need to work through egress problems correctly and efficiently under exam conditions.
Study PA on AREprep
AREprep's PA flashcards and practice exams are built around the actual NCARB exam guide - so every study session targets what the exam tests.