Spiral Stair
Spiral-shaped staircase with a central column.
A spiral stair is a spiral-shaped staircase in which winder treads are fixed radially to a central column — the newel. It usually forms a circular plan and differs from a helical staircase in having a continuous central column. For dwellings, relaxed requirements apply: the going at the walking line must be at least 230 mm and the usable stair width between newel and handrail at least 50–80 cm, depending on use.