Final answer:
A stair or ladder becomes necessary when there is a break in elevation of 30 inches or more, which is a widely accepted safety standard generally reflected in building codes.
Step-by-step explanation:
The break in elevation that typically necessitates the use of stairs or a ladder is 30 inches or more. For heights less than this, a ramp or a single step may be sufficient, but for safety and accessibility, stairs or a ladder are generally installed when the elevation change exceeds this value. Building codes may vary slightly by location, but the 30-inch rule is a widely accepted standard used to determine when a higher level can no longer be safely accessed by simply stepping up. It is important to consult local building codes, as they can provide specific guidelines for situations requiring stairways or ladders.