The measurements of a stair, in particular the rise (height) and run (depth) of the steps, should remain consistent throughout the stairs.
The following stair measurements are important:
- The rise of each step is measured from the top of one tread to the top of the next tread. It is not the physical height of the riser; the latter excludes the thickness of the tread. A person using the stairs would move this distance vertically for each step they take. In Ontario, the allowable range for a rise is 125mm (4-7/8”) to 200mm (7-7/8”) [OBC Table 188.8.131.52].
- The tread depth of a step is measured from the edge of the bullnose to the face of the vertical riser; if the steps have no bullnose, it is the same as the run; otherwise it is the run plus the extent of one bullnose.
- The run of each step is measured from the face of a vertical riser to the face of the next riser up. A person using the stairs would move this distance forward with each step they take. In Ontario, the allowable range for a run 210mm (8-1/4”) to 355mm (14”) [OBC Table 184.108.40.206].
- To avoid confusion, the number of steps in a set of stairs is always the number of risers, not the number of treads.
- The total run of the stairs is the horizontal distance from the face of the first riser to the face of the last riser. It is often not simply the sum of the individual tread lengths due to the bullnose overlapping between treads
- The total rise of the stairs is the height between floors (or landings) that the flight of stairs is spanning.
- The slope or pitch of the stairs is the ratio between the rise and the run (not the tread depth, due to the nosing). The pitch line is the imaginary line along the tip of the nosing of the treads.
- Headroom is the height above the top of a tread to the ceiling above it. Per Ontario Building Code, the minimum headroom is 1,950mm (6ft 5”) [OBC 220.127.116.11].
- Walkline – for curved stairs, the inner radius of the curve may result in very narrow treads. The “walkline” is the imaginary line 12” away from the inner edge on which people are expected to walk.