Stair details refer to the standard requirements governing each of the various components of a flight of stairs. Regulated by building codes, especially in conditions serving emergency public egress, stair details specify the height and depth of risers and treads, the widths of stairs for differing occupancy loads, the placement and dimensions of handrails and guardrails, and typical construction methods for fabricating a flight of stairs.
Responding to the movement of the human body, the sizes and relationships of stair risers and treads are regulated to make vertical motion safe and easy. Steep stairs make climbing more tiring and dangerous, while shallow stairs are awkward and inefficient for our human stride. Buildings codes have been created to control the minimum and maximum measurements of risers and treads.
As general rules of thumb for achieving comfortable relationships between riser and tread dimensions, the following formulas can be used:
Tread (inches) + 2x Riser (inches) = 24”-25” (26” for exterior stairs)
Riser (inches) x Tread (inches) = 72”-75”
Riser Height: 4" | 100 mm min.; 7" | 180 mm max.
Tread Depth: 11" | 280 mm min.
Nosing Protrusion: 1.5" | 38 mm max.
Nosing Radius: .5" | 13 mm max.
Stair widths are based on the use and occupancy loads of adjacent spaces and must be serviced with handrails on one or both sides depending on the stair width. For stairs serving a single user (typically private residential), a minimum of 36” | 91 cm is required. In general public spaces a minimum of 44” | 112 cm must be met—providing ample space for one person and allowing the tight passage of two people. Comfortable two person stair widths range between 49” | 125 cm to 60” | 152 cm. For three simultaneous users, a minimum of 74” | 188 cm is recommended. Handrails must be placed every 60” | 152 cm.
Consult the building code for details on specific occupancy loads.
1 Person (Private): 36” | 91 cm
1-2 People (Min. Public): 44” | 112 cm
2 People: 49” | 125 cm
2 People (Comfortable): 60” | 152 cm
3 People: 74” | 188 cm
Human Body Accommodation: 22” | 56 cm
Stair Widths front elevations, front (people)