Building stairs under the International Building Code provides measurements that have existed since early Roman times. The Roman architect, Vitruvius devised a guide for the Roman Emperor Caesar Augustus outlining desirable dimensions for building steps. Several minor changes have occurred since then, resulting in modern day dimensions which are all built to satisfy modern building codes.
The fact that every stair be exactly the same is not only critical for building stairs, but for providing for their safety. Figures for the United States alone, report that over approximately 4,000 people have been killed, and a little over 2 million injured seriously due to accidents on stairs and stairwells.
In order to discuss stairs, some terminology must first be explained and understood. The term, unit run is the actual step itself, or thread; the unit rise is the distance from one step above the next step. According to the 2000 International Code Council recommendations, unit runs should be no less than 10 inches (where a person steps) and rise to the next step no more than 7 and ¾ inches. The normally prescribed width in residences is approximately 2 feet, 8 inches, but where 3 feet is better, 3 feet, 6 inches is recommended for a normal occupancy standard.
In order to build stairs, a calculation for a stair stringer (to what the unit run and unit rise attach) must be obtained. The calculation is taken from the ground to the finished floor, or the “total rise.” Once these dimensions are known, the calculation is derived. Divide the total rise by the maximum riser height. For example, if your total height is 53 inches and your unit rise is 7 inches, dividing these will bring a dimension of 7.57. If you round this out to 8 inches, you will need 8 risers. If the dimension of the risers calculation is known, all that is left to do is to determine the riser height. This is done by dividing the total rise by the number of risers.
Landings and Balustrades
Normal fire and building codes restrict the rise of stairs to not more than 12 feet. At this point a landing must be provided which will have a length at least the same as the width of the steps leading up to it. Recent building code revisions have reduced the openings between balusters to not larger than 4 inches. This reduction has been incorporated to minimize injury to children, who could crawl between the normally allowed 8 inches, causing injury to them.
According to building codes, each balustrade must have a handrail as a topping, of at least 30, but not more than 38 inches above it, to provide for a person’s grip. This topping can be somewhere between 1 to 3 inches. It can be mounted on a wall, in which case, it needs to be 11/2 inches clear of the wall to facilitate gripping by persons climbing the stairs. In relation to accidents, the handrail is probably the single most important safeguard incorporated into building stairs under the International Building Code.