A Ship's Ladder is an inexpensive way to get to the roof for maintenance.
Roof Access is critical in commercial buildings especially if there is mechanical equipment located on the roof (flat roof). The traditional 30"x36" roof hatch and vertical ladder are inadequate. Maintenance of both the roof and the equipment located there require easy and safe access for inspection and bringing tools and filters onto the roof. The taller the building the more necessary this roof access becomes.
A Ship's Ladder and Roof Hatch are the least expensive way to meet this need for maintenance access.
Very High Ladders require require special consideration of OSHA regulations. A cage around the ladder may be required if the rise is more than 20'.
More about the 'How To' is available here.