In designing any sustainable structure, stairs, stair treads and landings are of paramount importance. There are tens of thousands of falls and injuries each year in the U.S. involving stairs and steps. Building codes, and such standards as The Americans with Disabilities Act Architectural Guidelines, rightfully regulate the design, dimensioning and detailing of stairs and their component parts to insure public safety. Stairs must therefore be well-designed, as well as strong, stable, secure, safe, non-combustible, slip-resistant and durable. They must also be easy to use and easily ‘read’, comprehended and understood by the traversing public.
Slabs of precast concrete lend themselves to stair construction, as they can be had in a wide variety of colors and textures, can be formed to any design, and are strong, durable, slip-resistant, non-combustible, stain-resistant and low maintenance. Depending on the final design of a staircase, they may also allow for relatively simple and speedy construction or installation.
The unique geometry of a staircase derives not only from its intended design appearance and configuration, but also by the parameters of its intended location, and by the codes and standards that regulate its design. A stair may be required to rise thirty feet, meaning it must have approximately 50 individual step risers of about seven inches each in height to reach that overall height. Codes may dictate that it have at least one or more intermediate landings, as rest and respite while ascending or descending. A tread depth of about eleven inches will likely be required, as will handrail heights of about 35 inches. The profile of each step’s tread may be required to incorporate a certain form of nosing, or projected forward lip. Most codes mandate a minimum stair width of 36 inches or more, and overall width may be significantly greater, as it is usually dependent on the total number of persons expected to use the stairs for access or egress.
As a result of all of the above considerations, most precast concrete stairs have risers in the six to seven inch range, treads of about 11 inches with a projected forward lip, and widths from 36 to 96 inches. To make the successive stair tread edges highly visible to anyone descending the stairs, a narrow contrasting color stripe and/or texture is often embedded into the forward lip edge of each stair tread.
Running parallel and at a slope, bracketing each side of a staircase’s steps are its stringers, which typically frame and support all of the individual steps. Either wood or, more commonly, steel stringers are used to attach and support precast concrete treads, via metal support angles at each end.