What’s considered safe for staircase variance?

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Stairs Stair Variability Max

When walking or climbing a staircase people naturally fall into a rhythm called cadence. People generally gain a cadence on stairs after two steps and maintain cadence throughout the staircase. Most people adjust naturally to small changes between steps, so when they experience a fall half way down or near the end of the stairs, step variability comes into question. There is an acceptable limit for variability between each riser or step height for all staircases and it is established by the Uniform and International Building Codes. This limit has changed from 3/16” in 1961, to 1/4” in 1973, to 3/8” in 1979. The maximum variance for both the rise and run for staircase risers has not changed since 1979.

 

Although standards organizations have identified uniform variance rules through the past fifty years, architects have been speculating on the best design for stairs from as early as 1691 with Joseph Moxon’s work called “Mechanical Exercises”. Other written works throughout history detail design for stairs in cathedrals and castles, both in Europe and Asia. In fact evidence of man-made stairs date back before the pyramids were built.

 

Put simply, since people started building structures, stairs have been in use. How stairs are constructed to maximize safety is an issue which will continue to evolve.