What is the minimum headroom requirement in all parts of the stairway?

The minimum headroom requirement in all parts of a stairway is crucial for ensuring safety and accessibility. A headroom clearance of 6'-8" is the standard measurement as specified in most building codes. This height is necessary to prevent occupants from bumping their heads on any part of the stairway structures, including the ceiling or overhead beams, especially in areas where people are likely to walk or maneuver.

Using a height of 6'-8" allows comfortable passage, even for taller individuals, and minimizes the risk of injury. The requirement is established by building codes that aim to create safe residential and commercial spaces, ensuring that stairway users can navigate without the hazard of hitting their heads or feeling cramped.

While other height options may be used in some contexts, they do not meet the general safety and accessibility standards found in many building regulations. Thus, 6'-8" is widely accepted as the minimum headroom for stairways, making it the correct answer for this question.