International Building Code 2504.1
Scope. The following requirements shall be met where
construction involves gypsum board, lath and plaster in vertical
and horizontal assemblies.
Wood framing.Wood supports for lath or gypsum
board, as well as wood stripping or furring, shall not be less
than 2 inches (51 mm) nominal thickness in the least dimension.
Exception: The minimum nominal dimension of wood
furring strips installed over solid backing shall not be less
than 1 inch by 2 inches (25 mm by 51 mm).
Studless partitions. The minimum thickness of
vertically erected studless solid plaster partitions of 3/8-inch
(9.5 mm) and 3/4-inch (19.1 mm) rib metal lath or
1/2-inch-thick (12.7 mm) long-length gypsum lath and gypsum
board partitions shall be 2 inches (51 mm).
International Building Code 2504.1.1
Wood framing.Wood supports for lath or gypsum
board, as well as wood stripping or furring, shall not be less
than 2 inches (51 mm) nominal thickness in the least dimension.
Exception: The minimum nominal dimension of wood
furring strips installed over solid backing shall not be less
than 1 inch by 2 inches (25 mm by 51 mm).
International Building Code 2504.1.2
Studless partitions. The minimum thickness of
vertically erected studless solid plaster partitions of 3/8-inch
(9.5 mm) and 3/4-inch (19.1 mm) rib metal lath or
1/2-inch-thick (12.7 mm) long-length gypsum lath and gypsum
board partitions shall be 2 inches (51 mm).