Stair design represents one of the more difficult parts of residential construction. Improperly designed stairs can be inconvenient or even dangerous. The angle, or incline, of a staircase is a function of several interrelated factors that include the home's layout, the desired step size and the requirements of the local building code.
A staircase design is described primarily by the following four terms: total rise, total run, tread width and riser height. The total rise is the distance from the lower finish floor to the upper finish floor. The total run is the distance from the beginning of the bottom of the staircase to the edge of the framed opening in the upper floor. The tread is the horizontal section of each individual step, and the riser is the vertical section.
Builders do not typically design a staircase in terms of incline but rather in terms of tread width and riser height. The ratio of these two numbers determines the overall angle of the staircase. For example, consider a staircase with risers that are 8 inches tall and treads that are 10 inches wide. The inverse tangent of this ratio calculates the angle in degrees: inverse tangent (8/10) = 38.6 degrees.
There are no universal rules regarding the ideal staircase incline. You'll often need to adjust the incline according to other design constraints, such as the amount of available floor space or physical limitations of people who might be using the staircase. In general, angles between 30 and 42 degrees are comfortable and safe. This corresponds to a riser height between 7 and 8 inches and a tread width between 9 and 11 inches.
Number of Steps
The staircase angle has the most influence on the usability of the staircase, so make this the dominant design decision. The number of steps should be chosen so as to allow for the most appropriate incline. To determine the number of steps, divide the total rise by the preferred riser height, then adjust the riser height slightly until this division results in an even number of steps.
- Independent Builder: Designing and Building a House Your Own Way; Sam Clark
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