The form of a stair, with its steps and angle of rise from one level to another, acts to reinforce the distinction between two levels. Compare it to a ramp, which as a sloping plane tends to feel like a linking of two floors or areas. This distinction works on a visual level (compare the elevations of each) as well as through bodily experience where ‘stepping’ action needed to use a stair exaggerates the separateness and distinctness to two different floor levels. Spiral stairs add and extra sense of separation through the visual and bodily corkscrew action. You may extend this example to consider how straight run stairs, switch back stairs, and right angle stairs, differ in the way they link different levels.
How does this help?
Stairs are not just pragmatic or functional elements in buildings. They can often be used to perform symbolic or ritualistic roles. The idea presented here is about considering the nature of the relationship between different levels in a project and how the choice of vertical circulation can be used to enhance that relationship. Of course, you may be required to use ramps to deal with accessibility issues or stairs for fire safety. However, nothing prevents you from exploiting their formal characteristics; similarly, nothing prevents you from proposing additional circulation elements if they enhance the usefulness or experiential quality of your design.
Source: Le Corbusier. “A stair separates one story from another; A ramp connects”, from Oeuvre Complet de 1929-1934, p.25.
Reading: Paul Frankl, The Principles of Architectural History: The Four Phases of Architectural Style, 1420-1900. This book is the only history of architecture based on how spaces are organised and how they are experienced bodily rather than by the eye.