What are the code requirements for roof decking?
Short answer. Under the IRC, roof decking must be rated structural panels, such as plywood or OSB with a span rating suited to the rafter or truss spacing, installed with edge support where the rating requires it and fastened on a set nailing schedule, commonly 8d nails at 6 inches along panel edges and 12 inches in the field, with tighter spacing in high wind areas. Asphalt shingles also require a solid deck rather than spaced boards.
The main requirements
- Rated panels: structural plywood or OSB bearing a grade stamp with a span rating and an exposure rating suited to construction.
- Span matched to framing: the IRC sheathing table ties panel span rating and thickness to rafter or truss spacing. On 24-inch framing, that typically means a 7/16 inch panel rated 24/16 or better.
- Edge support where required: some panel and spacing combinations need panel clips, blocking or tongue and groove edges between supports.
- Fastening: the IRC fastener table calls for nails along supported panel edges and at intermediate supports, commonly 6 and 12 inches apart, with closer spacing where design wind speeds are higher.
- Solid sheathing for shingles: asphalt shingles must be fastened to solidly sheathed decks, so old spaced board decks are overlaid or replaced during a shingle reroof.
Good practice the code assumes
- A gap of about 1/8 inch at panel ends and edges, as panel manufacturers recommend, so panels can expand in humid weather without buckling.
- Staggered end joints between rows.
- Nails driven into the framing, not beside it.
Special cases
Townhomes and attached homes can have fire-related sheathing rules near shared walls, and heavy roof coverings like tile may call for thicker decking. Check with the local building department for your situation.
Georgia enforcement
Georgia adopts the IRC as its residential code with state amendments, and cities and counties enforce it through permits and inspections. Exact provisions vary by code edition, so the local building department is the final authority.
See OSB vs plywood roof decking and roofing permits in Georgia.