The two principal elements in a stairway are the TREADS, which people walk on, and the STRINGERS (also called springing trees, strings, horses, and carriages), which support the treads. The simplest type of stairway, shown at the left in figure 6-69, consists of these two elements alone.

Additional parts commonly used in a finished stairway are shown at the right in figure 6-69. The stairway shown here has three stringers, each of which is sawed out of a single timber. For this reason, a stringer of this type is commonly called

a CUTOUT or SAWED stringer. On some stairways, the treads and risers are nailed to triangular stair blocks attached to straight-edged stringers.

A stairway that continues in the same straight line from one floor to the next is called a STRAIGHT-FLIGHT stairway. When space does NOT permit the construction of one of these, a CHANGE stairway (one that changes direction one or more times between floors) is installed. A change stairway in which there are platforms between sections is called a PLATFORM stairway. Stairs in a structure are divided into PRINCIPAL STAIRS and SERVICE STAIRS.

Principal stairs are those extending between floors above the basement and below the attic floor. Porch, basement, and attic stairs are service stairs. The lower ends of the stringers on porch, basement, and other stairs anchored on concrete are fastened with a kickplate (fig. 6-70).