(a) A stair
tower shall be a stairway which is separated from all floors or areas of the
building. Stair towers shall lead directly to grade by an exit
discharge.
(b) Stair towers shall
be Class A or Class B types in accordance with the following table:
Class A
Stair |
Class B Stair |
Minimum clear width in inches |
40"
|
36" |
Maximum height of riser |
7 1/2" |
8"
|
Minimum width of tread |
10" |
9"
|
Maximum angle of stairs in degrees |
33°
|
40°
|
Required handrails (Each handrail is allowed to
project 3" without decreasing minimumclear width) |
Both sides
|
One side under 40" in width, both sides 40" or more in width |
Maximum vertical distances between
landings |
9' |
12' |
(c)
The minimum width of landings shall be the same width as the stairs they serve.
Intermediate landings on straight run stairs shall have a minimum length of 3
feet.
(d) The narrowest width in a
stairway or landing serving a stairway shall determine the units of width for
the entire stairway.
(e) There
shall be no variation in the width of treads or the height of risers in any
flight. Variation in height of risers in adjacent flights shall not exceed 1/4
inch. All treads less than 10 inches, as measured horizontally between the face
of risers, shall have an effective projection of approximately 1 inch beyond
the face of the riser below.
(f)
Where material of stair treads and landings is such as to present a danger of
slipping, nonskid material shall be applied.
(g) No arrangement of treads known as winders
shall be permitted in required exit stairways.
(h) Stairways, landings, balconies, open
sided floors, and the like shall have well-secured handrails. The clear
distance between handrail and wall or other obstruction shall be not less than
1 1/2 inches. Longitudinal rails or balusters or both shall be provided.
Balusters shall be spaced not more than 6 inches apart. Longitudinal rails
shall not exceed 6 inches measured at right angles to the rails. The lowest
rail shall be measured vertically from the tread nosing.
(i) Handrails on stairs shall be not less
than 30 inches nor more than 34 inches above the upper surface of the tread,
measured vertically to the top of the rail, from a point on the tread 1 inch
back from the leading edge.
(j)
Handrails shall be provided on any stair landing, balcony, ramp, aisle, and the
like located along the edge of open sided floors or mezzanines to prevent falls
over the open side. Railings protecting open sides of landings, balconies,
mezzanines, and the like shall be at least 42 inches high.
(k) Storage or obstructions of any kind shall
not be permitted in stair towers.
(l) A door opening into a stair tower shall
at no point in its swing reduce the required units of width of the stair or
landing.
(m) Every door to a
stairway shall open onto a landing at least as wide as the stairs.
(n) Doors and frames used in connection with
stair towers shall be of approved label and be of substantial construction,
installed in a workmanlike manner, fitted with reliable hardware of approved
label and shall be of the side hinged, swing type.
(o) Stair tower doors shall swing with the
exit travel.
(p) Stair tower doors
shall be provided with fire exit hardware. Exterior doors from stair towers may
have panic hardware instead of fire exit hardware. No lock or other device
which prevents egress shall be permitted on the doors during any period of
occupancy.
(q) Stair tower doors
shall be a minimum of 32 inches in width. Doors used in connection with stair
towers shall be a minimum of 6 feet, 8 inches in height.
(r) Outside stairs shall be considered an
exit when they meet the following conditions:
(1) Outside stairs shall meet the conditions
listed in subsections (b)-(d), (f)-(j) and (l)-(q).
(2) Outside stairs shall only serve as an
exit for floors three or fewer stories above grade.
(3) Outside stairs shall be accessible and
unobstructed at all times of occupancy.
(4) Outside stairs shall be of substantial
construction and installed in a workmanlike manner. Combustible construction
may be used when floor panels are permitted to be combustible construction in
the construction tables. Wood stringers shall be a minimum size of 2 inches by
10 inches stock material when treads are butt nailed or a minimum of 2 inches
by 12 inches stock material when the stringers are sawed to accommodate the
treads.
(5) Handrails shall be
provided on both sides of outside stairs except that a handrail is not required
along a solid wall when the dimensions from the exterior handrail to the solid
wall is 36 inches or less.
(6) The
building exterior wall shall be fire rated in accordance with the rating
required for exterior walls in §
50.11 (relating to construction
tables).
(7) All doors opening onto
the outside stair and door assemblies located within 10 feet of any portion of
the outside stair shall have a fire rating the same as the rating required for
the exterior wall except that a door located at the top of the outside stair
need not be fire rated. All other openings within 10 feet of either side or
below the outside stair shall be glazed with 1/4 inch wire glass in steel
frames.