What is the minimum stair tread depth allowed without a nosings on stairways with solid risers

B) 11 inches

C) 12 inches

D) Nosings are always required.

Answer:

B) 11 inches


From the 2015 IRC-

R311.7.5.3 Nosings.

The radius of curvature at the nosing shall be no greater than 9/16 inch (14 mm). A nosing not less than 3/4 inch (19 mm) but not more than 11/4 inches (32 mm) shall be provided on stairways with solid risers. The greatest nosing projection shall not exceed the smallest nosing projection by more than 3/8 inch (9.5 mm) between two stories, including the nosing at the level of floors and landings. Beveling of nosings shall not exceed 1/2 inch (12.7 mm).