Final answer:
A nosing projection must be no less than 3/4 inch and no more than 1 1/4 inches on stairways with solid risers to ensure safety, compliance, and usability.
Step-by-step explanation:
A nosing projection on stairways with solid risers must be not less than 3/4 inch (19 mm) and not more than 1 1/4 inches (32 mm). Nosing is the part of the tread that protrudes over the riser beneath. This projection is important because it helps to provide more space on which a person can place their foot while ascending or descending a staircase, which can aid in preventing trips and falls. Ensuring that these measurements are adhered to is important for safety, building compliance, and usability of the stairway.
The horizontal projection to the front of a tread where most foot traffic frequently occurs. The nosing is the protrusion beyond the riser when vertical risers are used, or beyond the back of the tread below, when angled risers or no risers are used.