Construction of Stairs for the Stage: 1

One of the most common scenic elements that a theatre scene shop constructs is the stairway.

There are three main parts to a stair as the diagram to the left shows. The Tread is the horizontal surface on which the stair-climber walks. The Riser is the vertical element that fills the space between the back of one tread and the front of the next tread above it .  The Carriage provides the structural support to carry the weight of the stair-climber to whatever structure supports the two levels accessed by the stair and serves to hold the treads and risers in position.  Note that some stair units will omit the risers.

The carriage(s) of a stair may  be Open or Closed.  An open carriage stair (as illustrated above)  is easily identified by the saw-tooth profile of the stairs as seen from the side.  A closed carriage stair ( as illustrated below)  features carriages that are outside of the treads and risers and appear as a slope or ramp when seen from the side.

A stair may also be Independent or Dependent. An independent stair is self-supporting. Whether standing alone, apart from other scenery or pushed in place against and upper level, a person could climb from the bottom step to the top step without the unit tipping or falling over from lack of support.  By contrast, a dependent stair unit relies upon the structure of the upper level to support the weight of a person climbing the stair.  Note that in the example above, adding legs to the unsupported end(s) of the stair could convert a dependent stair to an independent stair at the cost of the visual clutter of the legs.

While the set designer specifies the outward appearance of a stairway seen onstage, depending upon your institutional organization, either a Production Manager, Technical Director, Master Carpenter or Scenic Carpenter makes the decisions on how a stair is constructed.  I have seen a number of methods over the years.  The most basic construction method relies upon brute strength.

The basic stair  usually starts with treads of ¾” plywood.  The plywood tread is supported front and back with structural lumber in the same way a basic stage platform might be.  Depending upon the width of the stair, strength necessary, standard construction practices of the shop and other matters, the stringers might be made of as substantial material as 2×4 to something as light as 1×3.

The outside edges of the tread are supported by carriages cut of ¾” plywood.  On a small stairway, the carriages may go all the way to the floor.

Stairs over 3′ wide might have one or more intermediate carriages between the outer ones to prevent unnecessary flex as a stair-climber places weight toward the center of the tread span.  If the stair is too tall  for a standard plywood carriage, because it cannot be cut out of a  4′ x 8′ sheet of plywood,  the carriage is often made of 1×12 or 2×12 instead.  The example to the left shows the construction of a stair with 2×12 stringers.

In all of these variations, the riser is mostly an after-thought, tacked in place after the rest of the structure is complete with little or no structural function. Usually, the front of one tread is even with the riser that fills in the space between it and the tread below.  This gives each step a flat front with no overhanging lip.

This type of stair unit has a number of drawbacks. Since most of the time, a designer will specify with a slight overhang of the tread over the riser, a decorative detail or Nosing must usually  be added to the front of each step.  This nosing is easily dislodged  by heavy foot-traffic.  Additionally, all of these construction methods tend to rely upon fasteners to bear most of the weight of each joint.  Those fasteners often hold into the laminated edge of plywood which is not a strong connection and does not serve as a good surface for glue.  The biggest drawback to the methods of stair construction described above is the failure of these construction methods to take advantage of all of the materials to provide structural support.  Consequently, some members such as carriages and stringers must be enlarged or extra ones added to provide support.  This adds considerable weight to the structure.

In the next installment, I will explore what I consider to be a better, stronger, lighter way of constructing stairs.

That’s enough for now! Have fun!  Be safe!

SJM

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One Response to “Construction of Stairs for the Stage: 1”

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