The spacing rules
GA-216-2010 Section 5 sets maximum fastener spacing for single-layer gypsum board on wood framing.
Nails, single nailing (Section 5.2):
- Ceilings: 7 in. o.c.
- Walls: 8 in. o.c.
Screws (Section 5.4):
- Framing at 16 in. o.c.: 12 in. o.c. on ceilings, 16 in. o.c. on walls
- Framing at 24 in. o.c.: 12 in. o.c. on both walls and ceilings
The traps
- Swapping the nail values. Ceilings are 7 in., walls are 8 in.
- Using the 16 in. wall screw spacing on 24 in. framing. With studs at 24 in. o.c., wall screws drop to 12 in. o.c.
- Mixing nails and screws. 12 in. is a screw spacing on ceilings; 7 in. and 8 in. are nail spacings.
Counting fasteners in a line
With a fastener at each end and the rest at the maximum spacing:
Spaces = line length ÷ spacing, rounded up to a whole number
Fasteners = spaces + 1
The +1 is the step people drop: the number of spaces is not the number of fasteners.
Worked examples
Screws on a wall stud at 16 in. o.c., 96 in. long. Wall screws may be 16 in. o.c. Spaces = 96 ÷ 16 = 6, so screws = 6 + 1 = 7. A count of 6 is the spaces. A count of 9 uses 12 in. spacing (8 spaces + 1), which applies only to ceilings or 24 in. framing. A count of 13 uses the 8 in. wall nail spacing (12 spaces + 1).
Nails on a ceiling joist, 144 in. line (a 12 ft board). Ceiling nails may be no more than 7 in. o.c. Spaces = 144 ÷ 7 = 20.57, which rounds up to 21 so no space exceeds 7 in. Nails = 21 + 1 = 22. Rounding down to 20 spaces gives 7.2 in. gaps, over the limit. A count of 19 uses the 8 in. wall nail spacing, and 13 uses the 12 in. ceiling screw spacing.