What is the minimum nosing size?

What is the minimum nosing size?

• A. 25 mm
• B. 20 mm
• C. 30 mm
• D. 15 mm

Answer: (A)

Stair nosing size is about how far the tread edge overhangs the riser to provide a safe, visible edge for stepping. Codes set a minimum projection to ensure there’s enough grip and footing, reducing the risk of catching a toe or slipping. In this case, 25 millimeters (about 1 inch) is the smallest projection that typically meets that safety minimum. A smaller measurement, like 20 or 15 millimeters, would not meet the required minimum and could compromise safety or compliance. A larger value, such as 30 millimeters, does meet the safety intent as well, but the question asks for the minimum, so 25 millimeters is the correct threshold.

Stair nosing size is about how far the tread edge overhangs the riser to provide a safe, visible edge for stepping. Codes set a minimum projection to ensure there’s enough grip and footing, reducing the risk of catching a toe or slipping. In this case, 25 millimeters (about 1 inch) is the smallest projection that typically meets that safety minimum. A smaller measurement, like 20 or 15 millimeters, would not meet the required minimum and could compromise safety or compliance. A larger value, such as 30 millimeters, does meet the safety intent as well, but the question asks for the minimum, so 25 millimeters is the correct threshold.