A spiral staircase is a stair whose treads wind around a vertical axis (the centre newel), so that it climbs in a circular or oval shape. Other names include winder stair, helical stair and spiral stair. It is a space-saving solution, particularly useful where floor area is limited.
Forms of spiral staircases
- Full-circle spiral — all treads turn around a central post
- Half-circle spiral — a semicircle, often placed against a wall
- Quarter-turn (winder) stair — triangular winder treads where the stair changes direction
- Helical stair — an oval, luxurious form without a central newel
Construction
A spiral staircase can be built in different ways:
- Newel post stair — all treads attach at one end to a central steel or timber post
- String stair — two curved strings on either side of the treads
- Cantilever stair — treads anchored into the wall with no centre post or string
- Helical balustrade — a curved handrail running with the stair adds stiffness
Applications
Spiral staircases are found in:
- Mezzanine connections — open connection to an upper level
- Office buildings — as a sculptural element in foyers and atriums
- Small dwellings — to save valuable floor area
- Garden buildings and lofts — as the only access to a second level
- Historic buildings — towers and castles with classic stone newel stairs
Building regulations
Most national building codes set minimum dimensions for stairs: tread depth on the walking line, riser height and width. For a second stair (e.g. to a mezzanine or loft) milder requirements often apply, which makes spiral staircases popular there.
Things to watch
- Tread depth at the inner edge — at least about 10 cm in a residential context
- Furniture transport — a winding stair is difficult for large pieces
- Safety — children and elderly users can slip on the narrow inner edge
- Handrails — at least one side is required, often both
Related terms
- Stair
- Tread depth
- Riser
- Balustrade
- Landing
- Newel post
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