What size plywood do you need for roof decking?
Short answer. For rafters or trusses 24 inches apart, the common choice is 1/2 inch (15/32) plywood or 7/16 inch OSB with edge clips, and 5/8 inch gives a stiffer deck. For 16-inch spacing the code allows thinner panels, but most roofers still use 7/16 or 1/2 inch because it walks better and holds nails better, and every panel is a 4 by 8 foot sheet laid long side across the framing.
Read the span rating
Every structural panel has a stamp with two numbers, such as 32/16. The first is the maximum roof framing spacing in inches the panel is rated for. The residential code's span table pairs each rating with a minimum thickness, and panels used at their limit between rafters often need edge support such as metal H-clips at the seams.
Common choices
- 7/16 inch OSB (24/16). The most common deck on newer Georgia homes with trusses 24 inches on center, installed with clips.
- 15/32 or 1/2 inch plywood (32/16). A solid, common choice for 24-inch framing.
- 19/32 or 5/8 inch. Stiffer, with less sag between rafters and better nail holding. Often used on wider spacing or where a firm deck under heavy roofing is wanted.
Installation details
- Lay the long 8-foot side across the framing and stagger the end joints.
- Leave about 1/8 inch between panels so they can swell without buckling.
- Ends must land on framing.
- Use Exposure 1 rated panels, which tolerate getting wet during construction.
When replacing a few sheets
Match the existing thickness. A thinner patch sits low and a thicker one sits high, and either shows through new shingles as a visible step. If the old deck is board lumber, the replacement may need shims to match.
See the panel comparison in OSB vs plywood roof decking.