Stairs can be dangerous. Falls from stairs kill thousands of people each year in the United States and injure millions more. While there are no universally accepted standards for the design of stair steps, there are general guidelines intended to reduce the risk of accidents. Local building and fire codes contain rules to ensure stair safety, and some have adopted the provisions of the national building code established by the Building Officials and Code Administration (BOCA).
The most significant safety feature of steps is that they be uniform in height. A sudden departure from an even gradation can cause you to misstep, so building codes generally require tight tolerances on the variation in riser height. The BOCA code also specifies a maximum height for each step of eight and one-quarter inches. Some codes restrict this height even further, limiting the rise to only seven inches.
The pitch of a staircase is how steep it is, specifically the angle from the same point on one step to the next one. Those who study stairs believe a pitch of between 20 and 50 degrees is safe, and being within the range of 30 to 35 degrees is best. Another rule of thumb for riser and tread design is that the sum of the two dimensions be between 17 and 17 and one-half inches. If a riser is seven inches high the tread depth should be no more than 10 and one-half inches deep. These dimensions also result in a safe pitch angle of 34 degrees.
The BOCA guidelines also specify a minimum tread depth of nine inches and allow for a one inch protrusion, which is known as nosing. Some safety groups instead suggest a minimum tread of 11 inches. As with riser height, it is important that the tread depth be as consistent as possible to avoid causing you to stumble.
Local codes typically specify stair step width limits. Usually the minimum for residences is from two feet eight inches to three feet six inches. There are no maximum widths, but stairs wider than 44 inches may require hand rails.
Local codes may require landings for staircases that rise more than a total of 12 feet. If so, the length of the landing should be equal to or greater than the width of the steps.