User:Acroterion/Scissor stair

A scissor stair or interlocking stair is a configuration of stairways in which two separate stairs are intertwined, crossing each other at each floor so the landings for each stair path alternate in position at each floor. The device is commonly used to consolidate two separate stairways into a single space or enclosure, creating a saving in the space and volume occupied by the combined stairway, but with the same user capacity as two stairs of the same width. The device is commonly employed in high-rise construction to create a compact stair enclosure with two stairway paths.

Such arrangements were permitted in New York City until 2008, when they were prohibited in buildings of more than 12 stories.