Genie_Girl: Staircases

Staircases, relied upon by many people for vertical transportation on a daily basis, can be found in homes, schools, and buildings of all types. Virtually all buildings with 2 or more floors require stairs, even those that rely on elevators and escalators to transport most people.

During the latter half of the Stone Age, neolithic people climbed steep mountain slopes using rocks and roots to gain a foothold. Eventually, these footholds were shaped into permanent steps. Many of these natural stair formations can still be seen today. Logs were eventually carved out with notches and placed against walls for the purpose of climbing. These “portable stairs”, which are still used by West Africa’s Dogon people, are examples of the first manmade stairways.

Ancient architecture contains many examples of stairways, including the pyramid El Castillo in Chichen Itza, Mexico, built between the years 900 and 1200 AD. This pyramid has a square base that measures 60 yards on each side. Each of the four sides that slant toward the peak contains a massive staircase with 91 steps. The upper platform contains a single step. The 365 steps in the pyramid (4 • 91 + 1 = 365) correspond to the number of days in the solar year. Because of this, it is believed that the pyramid was partly designed for worship of the sun.

When people use stairways today, they rely on the fact that the riser height (vertical distance) and tread length (horizontal distance) of stairs are predictable and consistent. This allows people to ascend or descend stairways without much difficulty. Despite this, stairs can be dangerous. The Consumer Product Safety Commission estimated that there were 1 million stair-related accidents in 1990, of which 85% occurred in homes.

Francois Blondel, a French architect, was the first person to establish a rule for staircase design. In 1675, while working for the Royal Academy of Architecture, Blondel devised the following formula: twice the riser height plus the tread depth equals 24 inches (25.5 in today’s inches). Blondel’s formula, which is still widely used today, suffers drawbacks when applied to staircases that have unusually high or low rise heights.

Recent building codes have more stringent requirements for staircase design. Prior to 1991, the Building Officials and Code Administrators (BOCA) required riser heights of at most 8.25 inches and tread depths of at least 9 inches. In 1991, BOCA modified the code such that riser heights must be between 4 and 7 inches and tread depth must be a minimum of 11 inches. This change, which caused considerable debate among builders and architects, was initiated by the Consumer Product Safety Commission’s 1990 report. Most objections focused on the issue of the cost to implement these new requirements. Other objections were related to the fact that these longer staircases would compromise the amount of living space. Interestingly, a 7-inch riser and an 11-inch tread yield 25 inches when Blondel’s formula is applied.

Escalators also provide vertical transportation. Escalators consist of a continuously moving handrail and stairway. Modern escalators provide one of the most efficient methods for moving large numbers of people. The first escalators were installed in 1900 in New York and Paris. These early escalators did not actually have stairs. Instead, they resembled conveyor belts that rose with a slight incline. The next generation of escalators added small strips of wood to provide better traction. Modern escalators, which can transport over 100 people in one minute, consist of a continuous series of steps that run on roller chains.