Stair geometry is one of the most important things a steel detailer must get right. If the rise, tread, or angle is wrong, the stair will not fit between floors, and fabrication or site installation becomes a problem. Good stair geometry ensures comfort, safety, and proper alignment with structural levels.
Stairs allow individuals to move between different levels of a building or structure. They are an essential element in any multi-story building, providing a safe and convenient means of vertical transportation. Stairs consist of several components, each with its technical term.
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Stair Elements
To better understand the anatomy of stairs, let’s familiarize ourselves with some common technical terms used in the context of stairs:
1. Risers
The rise is the vertical distance between two consecutive steps.
The riser height shall be 7" (180mm) max. And 4" (102mm) min.
The typical comfortable height used in many projects:150 mm – 180 mm
If the riser is too high, the stair becomes uncomfortable and unsafe. If it is too low, the stair becomes unnecessarily long.
2. Tread (Tread Depth)
The tread is the horizontal distance of each step where the foot is placed.
Typical tread depth: 11" (280mm)
A proper tread depth provides enough space for safe footing.
3. Nosing Point and Nosing Line
The nosing point is the projecting part of the tread beyond the face of the riser. It is usually rounded to provide an aesthetically pleasing architectural effect.
The nosing line is an imaginary line that touches each tread and is parallel to the slope of the stair. It helps define the overall shape of the staircase.
4. Pitch or Slope
The pitch or slope refers to the angle at which the line of nosing of the stairs makes with the horizontal. It affects the overall design and comfort of the staircase
Standard stairs must be installed at angles between 30 to 50 degrees from the horizontal.
Typical stair angle:
30° – 38° for comfortable stairs
Industrial stairs may go up to 45°
5. Landings
Landings are level platforms at the top or bottom of a flight between floors. They provide a resting point and allow for changes in direction or elevation.
OSHA Regulations Related to Landings:
Stairway landings must be at least 30 inches deep and 22 inches wide at every 12 feet or less of vertical rise. Unprotected sides of landings must have standard 42 inch guardrail systems.
6. Stringers
Stringers are the sloping members that support the treads in a stair. They are typically located on either side of the staircase and provide structural stability.
Different Types of Stringer Sections:
Stringers play a crucial role in supporting the treads and providing structural stability to the staircase. They come in various shapes and materials, each with its own advantages and design considerations. Here are some common types of stringer sections:
- Channel or MC stringers
- HSS stringers
- Plates stringers
7. Headroom
Headroom is the minimum clear vertical distance between the tread and the ceiling. It ensures that individuals can comfortably walk up or down the stairs without hitting their heads.
Key Things Steel Detailers Must Check
When detailing steel stairs, always verify:
- Floor-to-floor level matches structural drawings
- Landing elevations are correct
- Stringer length matches stair angle
- Tread spacing is consistent
- Headroom clearance is adequate
Even a 10–20 mm error in stair geometry can create problems during installation.
Closing Line
In steel detailing, stairs may look simple in drawings, but their geometry must be precise. Correct rise, run, and stair angle ensure the fabricated stair fits perfectly on site without costly modifications.
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