What were the roof decking requirements in the 2018 IRC, and what changed in Georgia?

What the 2018 IRC required

• Wood structural panels: plywood or OSB meeting the panel standards, chosen by span rating from the sheathing table, such as 24/16 panels at 24 inch spacing.
• Edge support: blocking, tongue-and-groove edges or panel clips where the table called for them.
• Lumber decking: boards of minimum thickness for the rafter spacing, still seen on older homes.
• Fastening: per the fastening schedule, 8d common nails at 6 inches along panel edges and 12 inches at intermediate supports for typical roof panels, with closer spacing in high-wind areas.
• Solid decks for shingles: asphalt shingles must be fastened to solidly sheathed decks; spaced boards are allowed only for certain coverings such as wood shakes.

What changed

The 2021 IRC reduced the maximum field nailing for roof sheathing to 6 inches, matching the edges, based on updated wind load calculations, and tightened spacing near roof edges and gable ends in higher wind zones. Georgia's current code is the 2024 IRC with state amendments, so check with your building department on exactly how the nailing schedule applies to your project.

What it means for your roof

• Homes built under the 2018 code may have sheathing nailed at 12 inches in the field, which met code at the time.
• On a reroof, inspectors may expect replaced sheathing to be nailed to the current schedule, and some roofers renail existing decking as a best practice.
• Older homes with board decking may need new sheathing if gaps are too wide for shingles.

See OSB vs plywood roof decking and roofing permits in Georgia.