The length of stair horses or stringers may be greater or less than the stair length, depending on the construction that is used. The actual length of the horse or stringer is determined during the layout. A few construction styles are shown in Fig. 1.
The usual practice followed to determine stair length is to lay out to scale the total rise and run on a steel square as shown in Fig. 2.
Measuring between the two points on the legs of the square will give the stair length. While the stair length is not precisely the hypotenuse of a right triangle whose sides are the total rise and the total run, in practice it is considered to be. The error, as shown below, is slight. Stair length may also be calculated using either trigonometry or the sum-of-the-squares equation.
The length of the rough stock needed for layout will depend on the style of construction. In many cases it must be greater than the stair length.
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