The limits of tread depth and riser height are established in the International Residential Code (IRC). Treads can be no less than 10 inches deep and risers can be no greater than 7 ¾ inches high. However, following these guidelines does not necessarily guarantee a comfortable stair.
Early civilizations did not have codes to limit their stair configurations. Some early stairways would literally take your breath away! The steps of the Pyramid of the Sun in Mexico have a basic riser height of 11” and a tread depth of less than that. When climbing this stair as a teenager, I experienced discomfort at about the 3rd riser up.
On the other extreme is a stair located in the home of the Winchester Rifle company heiress, Sarah Winchester. Along with the numerous design elements meant to confuse ghosts, Mrs. Winchester had a problem with lifting up her feet very far. (http://www.winchestermysteryhouse.com/index.cfm) To make it easy for her to climb the stairs, she had the contractor build one of her staircases with 2” risers. It took over 50 steps to travel to the next floor! When I climbed this staircase, it was as close to a futile effort that I have ever come on a staircase. It only took one step to feel discomfort and falling down this set of stairs would take forever!!
A comfortable stair has riser height ranges from 6.5 to 7.5” and has a tread depth from 11 to 12”. The trade-off for stair comfort is the floor space lost from adding extra risers and depth to the treads. If, for example, all of the home’s bedrooms are on the upper floor, the need for stair comfort is a key design consideration since traveling up and down occurs numerous times each and every day.
When contemplating a new staircase, consider comfort as well as where to place it in your home or business.