Exterior stairs may be used as exits in lieu of interior stairs provided they comply with all of the requirements for interior stairs, except enclosure, and except as modified below:
(a) Capacity. The capacity of exterior stairs shall be as listed in table 6-1.
(b) Height limitation. No exterior stair shall exceed seventy-five feet or six stories in height.
(c) Construction. Exterior stairs shall be constructed entirely of noncombustible materials, except that in buildings classified in occupancy groups other than G, F, or H, of construction group II, located outside the fire districts, exterior stairs may be built of combustible materials when the buildings are two stories or thirty feet in height or less and have an occupant load not exceeding forty persons per floor above the street below. Exterior stairs shall be roofed, and shall be protected along their outer sides as required for exterior corridors in subdivision (f) of section 27-369 of this article. Treads, landings, and platforms shall be solid and unperforated. Risers may be partially open to permit water and snow to drain.
(d) Opening protective. In buildings four stories or fifty feet in height or more, there shall be no openings in the building walls adjoining exterior stairs other than one-quarter hour self-closing swinging fire doors, and no openings nearer than ten feet to the stair (measured horizontally) that are not provided with three-quarter hour opening protectives.
(e) Location. No exterior stair shall be located nearer than ten feet to an interior lot line.
(f) Discharge. Exterior stairs shall extend continuously to grade.