International Building Code 1914.1
General. Reinforced gypsum concrete shall comply
with the requirements of ASTM C 317 and ASTM C 956.
International Building Code 1914.2
Minimum thickness. The minimum thickness of reinforced
gypsum concrete shall be 2 inches (51 mm) except the
minimum required thickness shall be reduced to 11/2 inches (38
mm), provided the following conditions are satisfied:
1. The overall thickness, including the formboard, is not
less than 2 inches (51 mm).
2. The clear span of the gypsum concrete between supports
does not exceed 33 inches (838 mm).
3. Diaphragm action is not required.
4. The design live load does not exceed 40 pounds per
square foot (psf) (1915 Pa).