Building Design and Construction Handbook - Merritt - Ventech!

VERTICAL CIRCULATION 16.5
Facilities Accessible to and Usable by the Physically Handicapped,’’ A117.1, American
National Standards Institute, New York, NY 10018.)
16.3 STAIRS
Less space is required for stairs than for ramps, because steeper slopes can be used.
Maximum slope of stairs for comfort is estimated to be about 1 on 2 (27�), but this
angle frequently is exceeded for practical reasons. Exterior stairs generally range
in slope from 20� to 30�, interior stairs from 30� to 35�.
16.3.1 Types of Stairs
Generally, stairs are of the following types: straight, circular, curved, or spiral, or
a combination.
Straight stairs are stairs along which there is no change in direction on any
flight between two successive floors. There are several possible arrangements of
straight stairs. For example, they may be arranged in a straight run (Fig. 16.2a),
with a single flight between floors, or a series of flights without change in direction
(Fig. 16.2b). Also, straight stairs may permit a change in direction at an immediate
landing. When the stairs require a complete reversal of direction (Fig. 16.2c), they
are called parallel stairs. When successive flights are at an angle to each other,
usually 90� (Fig. 16.2d), they are called angle stairs. In addition, straight stairs
may be classified as scissors stairs when they comprise a pair of straight runs in
opposite directions and are placed on opposite sides of a fire-resistive wall (Fig.
16.2e).
Circular stairs when viewed from above appear to follow a circle with a single
center of curvature and large radius.
Curved stairs when viewed from above appear to follow a curve with two or
more centers of curvature, such as an ellipse.
Spiral stairs are similar to circular stairs except that the radius of curvature is
small and the stairs may be supported by a center post. Overall diameter of such
FIGURE 16.2 Arrangement of straight stairs: (a) a single flight between floors; (b) a series of
flights without change in direction; (c) parallel stairs; (d) angle stairs; (e) scissors stairs.