external ladder
A ladder mounted permanently on the outside of a structure for maintenance and access.
An external ladder on a structure is a series of rungs or footholds mounted permanently on its facade or external surface, generally in order to provide access for maintenance but possibly also for regular access or for use as an emergency escape. A ladder is a simple series of footholds and handholds, and is not a stairway.
The rungs or footholds remain fixed to the exterior and provide a climbing route along the structure. Maintenance is a common purpose, but regular access and emergency escape are also included.
A loose ladder brought to a building for temporary work is not a permanently mounted external ladder. Maintenance catwalks provide elevated walking surfaces, while this feature provides a sequence of climbing holds.