2021 IBC Chapter 10
Chapter 10 of the 2021 IBC makes sure people can get out. A means of egress has three parts: the exit access (rooms, aisles, and corridors leading to an exit), the exit (a protected element such as an enclosed stair), and the exit discharge (the path from the exit to the public way). This lesson does the planning math: how many people a space is assumed to hold, how wide the paths must be, how many exits are needed, how far apart they must sit, and how far anyone may have to walk. Lesson 10 covers the doors, stairs, and ramps themselves.
Occupant load is a design number, not a head count. You divide the floor area by the factor in Table 1004.5, which is the square feet allowed per person for that use. Some factors apply to gross area (the whole floor area within the walls) and some to net area (the actual occupied area, leaving out corridors, stairways, toilet rooms, mechanical rooms, and closets), so read the table's label for each row. Where the path of travel crosses intervening rooms, Section 1004.2 uses cumulative loads.
| Use (rows taught) | Square feet per person |
|---|---|
| Business areas | 150 gross |
| Mercantile sales floor | 60 gross (stock and shipping areas 300 gross) |
| Classroom | 20 net (shops and vocational rooms 50 net) |
| Assembly, tables and chairs (unconcentrated) | 15 net |
| Assembly, chairs only (concentrated) | 7 net |
| Assembly, standing space | 5 net |
| Residential (apartments) | 200 gross |
| Warehouse | 500 gross |
| Parking garage | 200 gross |
Three related rules help. Under Section 1004.8, the building official may accept the actual load of a call center or trading floor, but not less than one person per 50 square feet gross. Section 1004.5.1 lets a designer raise the load up to one person per 7 square feet of occupiable floor if every other requirement is met at the higher number. And fixed-seat assembly areas use the seat count (1004.6).
Width is capacity: the load served times a factor. Stairways use 0.3 inch per occupant (1005.3.1) and other components (doors, corridors, ramps) use 0.2 inch per occupant (1005.3.2). A building sprinklered throughout (903.3.1.1 or 903.3.1.2) that also has an emergency voice/alarm communication system (907.5.2.2) may use 0.2 inch for stairs (except in Groups H and I-2) and 0.15 inch for other components. For a stair serving several stories, the load of each story is used individually. Two more rules matter in the field. Width may not shrink along the path toward the public way (1005.4). And where several exits are required, losing any one must not leave less than 50 percent of the required capacity (1005.5). The minimum widths in other sections still apply to each component, so the capacity math often yields a number smaller than the minimum.
Table 1006.3.3 sets the count by the occupant load of the story: 1 to 500 needs two exits or exit access doorways, 501 to 1,000 needs three, and more than 1,000 needs four. That is the default. A story may have a single exit only where Section 1006.3.4 allows it. Table 1006.3.4(2) covers most groups. On the first story above or below grade plane, Groups A, B, E, F, M and U may have one exit for up to 49 occupants and 75 feet of travel, and Group S for up to 29. On the second story above grade plane only Groups B, F, M and S qualify, for up to 29 occupants and 75 feet. Third story and higher is not permitted. Groups B, F and S sprinklered under 903.3.1.1 may go to 100 feet. Table 1006.3.4(1) covers R-2 dwelling units: up to four units per story through the third story above grade plane, 125 feet of travel, with sprinklers and emergency escape and rescue openings. A space (not a whole story) with one exit or exit access doorway must also stay within Table 1006.2.1.
Common path is the part of the trip, from the most remote point, before an occupant has a choice of two separate exits. Table 1006.2.1 limits it. The rows below (sprinklered means the standard named in the table footnotes) show the most you can have with a single-exit space.
| Group | Max occupant load of the space | Common path, not sprinklered | Common path, sprinklered |
|---|---|---|---|
| A, E, M | 49 | 75 ft | 75 ft |
| B | 49 | 100 ft if load is 30 or less, 75 ft if over 30 | 100 ft |
| F | 49 | 75 ft | 100 ft |
| S | 29 | 100 ft | 100 ft |
| R-2 | 20 | not permitted | 125 ft |
When two exits or exit access doorways are required, they must be placed at least one-half of the maximum overall diagonal of the building or area served apart, measured in a straight line. In a building sprinklered throughout (903.3.1.1 or 903.3.1.2) the distance drops to one-third of the diagonal. Measure to any point on the width of a doorway, to the closest riser of an exit access stair, or to the start of an exit access ramp (1007.1.1.1). Two exits side by side satisfy the count but not the code: they can be blocked by the same fire.
Exit access travel distance is measured from the most remote point along the natural, unobstructed path to the entrance of an exit (1017.3).
| Group | Not sprinklered | Sprinklered |
|---|---|---|
| A, E, F-1, M, R, S-1 | 200 ft | 250 ft |
| B | 200 ft | 300 ft |
| F-2, S-2, U | 300 ft | 400 ft |
| I-1 | not permitted | 250 ft |
For Group B the sprinklered value needs an NFPA 13 system (903.3.1.1); for A, E, F-1, M, R, S-1 and I-1 either NFPA 13 or 13R counts. A one-story F-1 or S-1 with a ceiling at least 24 feet high and NFPA 13 sprinklers may reach 400 feet (1017.2.2).
Table 1020.2 sets the corridor rating. In Groups A, B, E, F, M, S, and U with a load over 30 served, the corridor needs a 1-hour rating if not sprinklered and none if sprinklered. Corridor walls are fire partitions (Section 708). Width comes from Table 1020.3: 44 inches for most uses, 36 inches where the occupant load served is under 50, and 72 inches in Group E where the load is 100 or more. A dead-end corridor may not exceed 20 feet, or 50 feet in Groups B, E, F, I-1, M, R-1, R-2, S, and U in a building sprinklered throughout with NFPA 13 (NFPA 13R does not count for this exception).
Worked example. A one-story Group B office is 50 feet by 120 feet, or 6,000 square feet. Load: 6,000 / 150 = 40 occupants. Exits: 40 is under 501, so Table 1006.3.3 calls for two exits unless the story qualifies for a single exit under Table 1006.3.4(2) (first-story Group B: up to 49 occupants and 75 feet of travel, 100 feet with NFPA 13). This plan uses two. Width: doors and corridors 40 x 0.2 = 8 inches, stairs 40 x 0.3 = 12 inches, but the minimums control: a 32-inch clear door, a 36-inch corridor, a 36-inch stair. Separation: the diagonal is the square root of 50 x 50 + 120 x 120, which is 130 feet, so the exits must be at least 65 feet apart (about 43 feet with sprinklers). Travel: 200 feet unsprinklered, 300 feet with NFPA 13.
In the field
A nonprofit renting a 2,100 net square foot community room wants to use it three ways: dinners at tables, lectures in rows of chairs, and standing receptions. The same room is 2,100 / 15 = 140 people with tables and chairs, 2,100 / 7 = 300 with chairs only, and 2,100 / 5 = 420 standing. The exits and width must fit the largest arrangement the owner will really use, and the sign or plan should say so. Ask how the room will be used before accepting the smaller number.
1. An inspector calculates the occupant load of a Group B office area of 4,500 square feet gross using Table 1004.5 (150 square feet gross per person). The load is:
2. A mercantile sales floor (Group M) is 3,000 square feet gross. Using the Table 1004.5 factor of 60 gross, the occupant load is:
3. A Group E classroom is 900 square feet net. At the Table 1004.5 classroom factor of 20 net, the occupant load is:
4. A church hall (Group A-3) has 1,500 square feet net of standing space for receptions. At 5 square feet net per person, the occupant load is:
5. The occupant load on one story of a Group B building is 520. How many exits or exit access doorways does Table 1006.3.3 require from that story?
6. A Group M store has an occupant load of 250. Using 0.2 inch per occupant for doors (no sprinkler and alarm reduction), the width required by capacity is:
7. A one-story stairway serves an occupant load of 150 in a Group B building with no sprinkler system. At 0.3 inch per occupant, the capacity-based width is:
8. A Group B building is sprinklered throughout with NFPA 13 and has an emergency voice/alarm communication system. For a stair serving 150 occupants, the reduced factor of 0.2 inch gives:
9. A Group B building sprinklered throughout has a maximum overall diagonal of 90 feet. What is the minimum separation for its two exits under Section 1007.1.1?
10. An inspector measures the farthest point of a sprinklered (NFPA 13) Group M store at 240 feet of exit access travel. Under Table 1017.2, this travel distance is:
11. An inspector measures 90 feet of common path of egress travel in a Group B space with an occupant load of 40 and no sprinklers. Under Table 1006.2.1, this is:
12. A Group B building is sprinklered throughout with NFPA 13. An inspector measures a dead-end corridor of 40 feet with two exits required. Under Section 1020.5, this dead end is:
13. A Group B corridor serves an occupant load of 120 people. Under Table 1020.3, what is the minimum corridor width?
14. When more than one exit is required, Section 1005.5 says that losing any one exit must not reduce the available capacity below what share of the required capacity?