helix stairway
A stairway arranged around a central axis in a circular path, with or without a central post or open shaft.
A helical stairway (often called a spiral stairway) consists of stairs arranged in a circular fashion around a central axis. There may or may not be a newel (a structural post) at the center of a helical stairway, and it can also rise around an open shaft or atrium.
Helical stairs are one of the most space-efficient configurations, but are generally difficult for many people to navigate, and almost totally impractical for carrying furniture or large objects. They are most often used in narrow towers (such as lighthouses and church spires) or in houses or bilevel apartments as a supplemental form of access.
This form of stairway should not be confused with a semihelix, in which each flight is only a half-circle. Interlocking helices are classified separately also.
