Unless a minimum tread depth is provided, what minimum nosing is required at the leading edge of treads?

The requirement for minimum nosing at the leading edge of treads is related to ensuring safety and accessibility in stair design. The correct answer indicates that a minimum nosing depth of 11 inches is necessary unless a specific minimum tread depth is provided. This measurement is important because it offers extra surface area for users to place their feet securely, thus preventing slips and falls when navigating stairs.

In stair design, nosing helps to enhance visibility and provides better footing, especially in environments that must comply with accessibility standards, such as the Americans with Disabilities Act (ADA). Measuring the nosing correctly is crucial; if it is less than the specified depth, it could compromise the safety and functionality of the stairs.

The other options might imply different interpretations of nosing requirements but do not align with standard safety and design practices laid out in building codes. Thereby, selecting 11 inches fulfills the need for safety and regulation compliance effectively.