Single layer systems: 1 in. long for 1/2 and 5/8
in. thick panels, spaced 8 in. OC along edges of board and 12 in. OC in the
field of board.
Two layer systems: First layer- 1 in. long for
1/2 and 5/8 in. thick panels, spaced 16 in. OC . Second layer- 1-5/8 in. long
for 1/2 in., 5/8 in. thick panels, spaced 16 in. OC with screws offset 8 in.
from first layer.