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21. Stairs and Other Challenging Structures
- Southern Illinois University Press
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279 21.1 Stairs and Ladders A stair is one of the most complex units of standard scenery to build or to draft. The complexity of stair units comes from the need for them to be comfortable for the human body, to elevate the actor to a given height, and to fit within a given space. Drafting them requires some understanding of the structural problems associated with them. Stairs are made up of the three components shown in figure 21.1 and defined in figure 21.2. Because the human body readily adapts to the rise and depth of a given step, a constant riser/tread relationship must be maintained. If the riser/tread relationship is not constant, the actor is forced to move awkwardly to compensate for the inconsistency, although at times this type of movement is a directorial/ design decision. At best this creates a strange stage picture; at worst, this situation can cause an accident. Several “rules of thumb” have been developed in the construction trades to aid in the determination of tread depth and riser height (fig. 21.3). These are not absolute rules but guidelines to use in determining the solution that best fits the circumstances. Terms and Formulas The run of a stair unit is determined by multiplying the tread depth times the number of treads. The rise of a stair equals the riser height times the number of risers. To maintain comfort, in an unrestricted area, the total run should equal 1⅓ times the total rise. Frequently , onstage space for stairs is very restricted, limited perhaps by other scenery or the theatre walls. Shortening the run dimension will, of course, increase the steepness of the stairs. Acceptable practice dictates that stair steepness not be more than 50° nor less than 20°. 21. Stairs and Other Challenging Structures 21.1 A stair unit COMPONENT DESCRIPTION STANDARD MATERIALS Tread Walking surface 2x12, ¾" ply (single or doubled) Riser Step height 1x lumber, plywood Carriage / stringer Structural member that supports treads and risers 2x12, 5/4x12, or ¾" ply with nailing cleats 21.2 Stair component materials 280 21.4 Front elevation and section of an open riser stair In the case of shop drawings, stair drawings frequently become more complex, since often multiple units are joined in order to employ existing elements. Figure 21.5 is an example of such a unit and includes railing as well as assembly notes. Even this is simple since it is a straight run stair, but it gives the reader an idea of the scope of the information that is useful for carpenters in the construction and assembly of such units. Design drawings of stair units are often nothing more than the information given on the ground plan unless the stair is highly ornamental or unusual. In addition to a top view, shop drawings should show two other views, usually front and side views or front and section views (fig. 21.4). Because of the increased number of dimensions and notes needed to detail tread, riser, and carriage arrangements , 1″ = 1′-0″ scale is often used. FORMULAS EXAMPLES Tread depth* + riser height = 17½" T+ R = 17.5" 10"+7½"= 17½" Tread depth + (2 x riser height) = 25" T+2R = 24"to 25" 10"+2 (7½") = 25" Tread depth x riser height = 75" T x R = 75" 10" x 7½" = 75" ADDITIONAL CONSIDERATIONS • Number of risers = total rise/riser height • Riser height = total rise/number of risers • Subtract the thickness of the tread from the first rise when laying out a carriage. • Add a center carriage for stairs wider than 2'-6" to assure tread stiffness. • Provide railings for all stairs but especially offstage stairs. The top edge of the handrail should be located 2'-8" above the tread at the nosing line. • Allow a minimum of 6'-8" (80") headroom for stairs located under a platform or through a trap. 21.3 Rules of thumb for stair construction [3.235.46.191] Project MUSE (2024-03-28 11:21 GMT) 281 21.2 Curved Stair Curved stairs are frequently used in theatrical productions. They require different specifications than standard straight-run units. While they can be very complex to build, especially circular stairs, small units are easily managed. Drawings typically show a minimum of two views and usually require notes to explain all the needs (fig. 21.6). Railings are particularly important features since construction must make provision for their inclusion early on; they are not add-on elements. 21.5...