10.5 Means of Egress & Fire-Resistance-Rated Construction
Key Takeaways
- Occupant load is calculated from IBC Table 1004.5 floor-area allowances, and the occupant load drives egress width, number of exits, and door swing
- Egress doors serving an occupant load of 50 or more must swing in the direction of egress; two exits are generally required once occupant load exceeds the table limit
- Egress width factors are 0.3 inch per occupant for stairways and 0.2 inch per occupant for other components in non-sprinklered buildings
- Fire walls, fire barriers, fire partitions, and smoke barriers are distinct assemblies with different continuity requirements — the names are not interchangeable
- Rated assemblies fail at their weakest point: opening protectives, dampers, and firestopped penetrations must carry ratings compatible with the assembly
Why These Two Chapters Dominate
Quick Answer: On the AZ ROC commercial trade exam, General Building Code is 9 of 100 items, and most of those questions come from two places in the 2018 IBC: Chapter 10, Means of Egress and Chapter 7, Fire and Smoke Protection Features. Both are table-driven, which makes them ideal open-book material — if your code book is tabbed.
A general building contractor does not design egress. But the contractor builds it, and the contractor is the one who gets a correction notice when a rated wall stops at the ceiling instead of the deck, when a hold-open device is screwed to a fire door, or when a plumbing penetration through a two-hour shaft is stuffed with fiberglass. These are field errors, not design errors, and they are exactly what the exam probes.
Means of Egress: The Chain
The IBC defines a means of egress as a continuous, unobstructed path from any occupied point to a public way, in three parts:
| Component | What it covers |
|---|---|
| Exit access | Corridors, aisles, and rooms leading to an exit |
| Exit | The protected portion — enclosed stairway, exit passageway, or exterior exit door |
| Exit discharge | From the exit to the public way |
Occupant Load Drives Everything
Occupant load comes from IBC Table 1004.5, which assigns a floor area allowance per occupant by function. Familiar values include roughly 100 sq ft gross per occupant for business areas, 15 net for classrooms, 15 net for assembly with tables and chairs, and 7 net for standing assembly space. Divide the applicable floor area by the allowance and round up.
Everything downstream follows from that number:
- Number of exits — a space needs a second exit once occupant load or travel distance exceeds the table limits for its occupancy.
- Door swing — an egress door serving an occupant load of 50 or more must swing in the direction of egress travel.
- Panic hardware — required on doors serving high-occupant-load assembly and educational spaces, and on rooms containing certain electrical equipment.
- Egress width — capacity is computed per occupant.
Egress Width Factors
| Component | Non-sprinklered | Sprinklered with alarm |
|---|---|---|
| Stairways | 0.3 in. per occupant | 0.2 in. per occupant |
| Other egress components (doors, corridors, ramps) | 0.2 in. per occupant | 0.15 in. per occupant |
Worked example. A business-occupancy floor of 12,000 gross sq ft at 100 sq ft per occupant carries an occupant load of 120. In a non-sprinklered building, the required stairway width is 120 × 0.3 = 36 inches, and the required door width is 120 × 0.2 = 24 inches — but minimum dimensions govern where they exceed the calculation, so the doors still must meet the code minimum clear width of 32 inches. Calculated width and minimum width are both floors; the larger controls.
Other constants worth tabbing: minimum corridor and egress ceiling height of 7 feet 6 inches in most cases, a 44-inch minimum corridor width for occupant loads of 50 or more, and the requirement that where two exits are required they be separated by at least one-half (or one-third, in sprinklered buildings) of the maximum overall diagonal of the area served.
Fire-Resistance-Rated Construction: Know the Four Names
IBC Chapter 7 defines several rated vertical assemblies that look identical on a drawing and behave very differently in the field. Confusing them is the classic exam trap.
| Assembly | Typical purpose | Continuity |
|---|---|---|
| Fire wall | Divides a building into separate buildings for code purposes | Foundation to or through the roof; structural stability maintained if construction on either side collapses |
| Fire barrier | Encloses shafts, exits, and separates occupancies or control areas | Floor to the floor or roof deck above, continuous through concealed spaces |
| Fire partition | Corridor walls, tenant separations, dwelling-unit separations | Floor to the underside of the floor or roof deck above, or to a rated ceiling membrane where permitted |
| Smoke barrier | Restricts smoke movement | Floor to deck above, continuous, with smoke dampers at penetrations |
The practical distinction is where the wall stops. A fire barrier that dies at a suspended acoustic ceiling is not a fire barrier. A fire partition may terminate at a rated ceiling assembly if the code permits it for that condition. Field crews build both walls the same way unless the plans and the superintendent are explicit, which is why this shows up on inspections.
Opening Protectives
A rated wall is only as good as its holes. Opening protectives carry their own ratings, and they are generally lower than the wall's:
| Wall rating | Typical door/opening rating |
|---|---|
| 3-hour fire wall | 3-hour door |
| 2-hour fire barrier (shaft, exit enclosure) | 1½-hour door |
| 1-hour fire barrier | ¾-hour (45-minute) door |
| 1-hour fire partition (corridor) | ⅓-hour (20-minute) door |
Field rules that follow: fire doors must be self-closing or automatic-closing and positive-latching; hold-open devices must be listed and tied to the alarm system; and nothing may be field-drilled, cut, or screwed into a labeled door or frame outside the manufacturer's listing. Removing a door's label voids the assembly.
Penetrations and Joints
Every pipe, duct, conduit, and cable tray that crosses a rated assembly needs a listed firestop system — an F-rating for flame passage and, where required, a T-rating limiting temperature rise on the unexposed side. Head-of-wall and floor-to-wall joints need listed joint systems. Ducts crossing rated assemblies need fire dampers; ducts crossing smoke barriers need smoke dampers; some conditions require combination dampers.
Warning: the single most common field failure in this area is a mechanical or electrical sub cutting a clean penetration through a rated wall late in the job and packing it with unlisted material. It is the general contractor's rated assembly, and the general contractor's correction notice.
A non-sprinklered business-occupancy floor has an occupant load of 200. What minimum stairway width does the IBC egress capacity calculation produce?
An egress door serves a room with an occupant load of 60. What does the IBC require of the door?
Which assembly must be continuous from the floor to the underside of the floor or roof deck above and through concealed spaces?
A plumbing subcontractor cores a new 4-inch penetration through a 2-hour shaft wall and packs the annular space with unfaced fiberglass batt. What is wrong?