What OSB roof decking thickness does the building code require?
Reading the stamp
Every structural OSB panel carries a grade stamp showing its span rating, thickness, exposure rating and the standard it meets. For roofs, look for:
- Span rating: such as 24/16, where the first number is the maximum roof support spacing in inches.
- Exposure 1: made to withstand weather during normal construction delays, the usual grade for roof sheathing.
- Thickness: 7/16 inch is common; 15/32, 1/2 and 19/32 inch panels allow longer spans or stiffer decks.
Edge support and H-clips
Where panel edges fall between rafters, the code requires support for panels that need it, provided by blocking, tongue-and-groove edges, or panel edge clips, commonly called H-clips. Clips also hold the recommended small gap between panels so they can expand when damp.
Nailing
The code's fastening table sets nail type and spacing for roof sheathing. For 3/8 to 1/2 inch panels, recent editions call for 8d common nails at 6 inches along edges and 6 inches at intermediate supports, with closer spacing near roof edges in higher wind zones. Older editions allowed 12 inches in the field, so older roofs may be nailed more sparsely.
Georgia specifics
Georgia has enforced the 2024 IRC with state amendments since January 1, 2026, and local inspectors may look at sheathing when a reroof includes significant deck replacement. Ask your building department about local requirements.
Replacing OSB on a reroof
Match the existing thickness so the surface stays flush, keep the span rating suited to the framing, gap panels as recommended, and nail to the current schedule. See OSB vs plywood roof decking and roofing permits in Georgia.