What roof decking thickness does the building code require?
How the code table works
The IRC's wood structural panel table lists each span rating with its minimum thickness and the maximum roof support spacing allowed, both with and without edge support, along with the loads the panel is rated to carry. You match your framing spacing to a panel whose roof span number meets or exceeds it. The span rating printed on the panel stamp is what inspectors check.
Typical outcomes
- Trusses at 24 inches: 7/16 inch panels rated 24/16, or 15/32 inch plywood rated 32/16, are common choices. A 3/8 inch 24/0 panel needs edge support at this spacing.
- Rafters at 16 inches: thinner panels are allowed, but most builders still use 7/16 or 1/2 inch for stiffness.
- Heavier roof coverings: tile and slate may call for thicker panels or engineered design.
Other rules that interact
- Asphalt shingles must go on a solid deck.
- The nailing schedule sets how panels attach to the framing.
- Shingle manufacturers list their own minimum deck requirements in their installation instructions.
Georgia specifics
Georgia adopts the IRC as its residential code with state amendments, enforced locally. Existing roofs are not required to be upgraded until work is done, but when damaged decking is replaced during a reroof, new sheets must meet current rules. If you find thin 3/8 inch decking sagging between trusses, the reroof is the time to replace or reinforce it.
See OSB vs plywood roof decking and roofing permits in Georgia.