Building codes make a distinction between occupied and unoccupied roofs. Unoccupied roofs need to be accessed for equipment servicing; a person has a specific reason to be there. Codes specify that the door should be unlocked from the roof side so that nobody is accidentally locked outside. These doors are often locked from the inside so that entry to the roof is controlled. Stairways or fixed ladders are adequate for egress for service personnel.
When the public is expected to have access to the roof, it becomes occupied. An occupied roof is treated like a room in building codes; roof egress requirements may be identical to the egress specified for stories in the building. They're based on the expected occupancy and the size of the area. The International Building Code classifies buildings into groups based on occupancy levels with differing egress requirements.
Occupied Roof Egress Requirements
Typically at least two egress points are required, with access to an exit from the roof that leads to an exit from the roof or to an exit to the next story down. Height and width clearance for exit routes is often specified, along with fire doors and hardware standards. Signage and lighting for the egress route is another factor. Accessibility is also an issue; ramps and staircases are subject to code requirements, depending on the category.
Building codes are governed by state and provincial authorities and based on the International Building Code. For older buildings, compliance with building codes can be problematic. Egress clearance and obstruction requirements, for example, may call for more space than older buildings have. Occupancy levels may be less or more controlled than building codes anticipated. Authorities usually allow for a process to apply for modifications that don't compromise safety standards. A detailed application process must be followed.