Ergonomics of Staircase Design
Discover the 'Blondel Rule' and why a few millimeters of difference in riser height can make a staircase tiring or dangerous.
The Science of the Human Stride
A staircase is a machine for vertical travel. If the steps are too high, they become exhausting; if they are too low, they become a tripping hazard. In the $17$th century, French architect Francois Blondel identified a relationship between the Riser ($R$) and the Tread ($T$) based on the average human stride length (approximately $630$mm to $650$mm).
The Blondel / 2R+T Rule
For perfect comfort, the goal is exactly $600$mm to $630$mm.
Key Components of a Staircase
- Riser: The vertical height of each step. Modern codes usually cap this at $190$mm for residential and $150$mm for public buildings.
- Tread: The horizontal surface where you place your foot. It should be deep enough to support at least $70\%$ of an adult foot (min $250$mm).
- Nosing: The small projection ($20$mm-$30$mm) of the tread beyond the riser, which provides extra footing space without increasing the staircase length.
- Pitch/Angle: The slope of the stairs. Residential stairs should ideally be between $30^\circ$ and $37^\circ$. Anything over $45^\circ$ is considered a "steep" stair.
Safety and Code Compliance
Consistency is the most important rule in staircase construction. Even a $5$mm variation between the height of two steps can cause the brain to miscalculate the stride, leading to falls. This is why the Total Height must be divided precisely into equal risers, even if the resulting number has decimals (which are then rounded for the formwork).
Frequently Asked Questions (FAQ)
What is 'Headroom'?
Headroom is the vertical distance between the tip of the stair nosing and the ceiling above. Building codes strictly require a minimum headroom of $2000$mm ($2.0$ meters) to prevent tall users from hitting their heads while descending.