STAIRS

• Riser-Tread formula: Sometimes the stair parameters will be something like riser plus tread equals 17–18 inches (432–457 mm);^[18] another formula is 2 times riser + tread equals 24.6 inches (625 mm), the length of a stride.^[5] Thus a 7 inches (178 mm) rise and a 10.6 inches (269 mm) tread exactly meets this code. If only a 2 inches (51 mm) rise is used then a 20.6 inches (523 mm) tread is required. This is based on the principle that a low rise is more like walking up a gentle incline and so the natural swing of the leg will be longer.