What is the minimum roof decking thickness?
How the code sets the minimum
The International Residential Code ties roof sheathing to the span rating stamped on each panel, such as 24/0 or 24/16. The first number is the maximum roof support spacing in inches. Common pairings from the code's sheathing table:
- 24/0, 3/8 inch minimum: 24 inch spacing with edge support, 20 inches without.
- 24/16, 7/16 inch minimum: 24 inch spacing with or without edge support.
- 32/16, 15/32 or 1/2 inch: up to 32 inch spacing with edge support.
Edge support means tongue-and-groove edges, blocking, or panel edge clips, often called H-clips, between rafters.
What Georgia homes typically have
Many newer Georgia homes are framed with trusses 24 inches apart and sheathed with 7/16 inch OSB, often with H-clips. Older homes with rafters 16 inches apart may have 1/2 inch plywood or 1x board decking.
Why thicker can be better
- Less sag between supports, so the roof plane stays flat.
- Better nail holding for shingles.
- More tolerance for foot traffic and heavy premium shingles.
Replacing damaged sheets
During a reroof, replacement panels should match the existing thickness so the surface stays flush, and meet the span rating for the framing. A 3/8 inch patch in a 7/16 inch deck leaves a visible dip.
Manufacturer rules
Shingle manufacturers publish their own deck requirements and may not warrant shingles over undersized or widely spaced decking, so check the installation instructions.
Georgia enforces the 2024 IRC with state amendments; confirm details with your local building department. See OSB vs plywood roof decking and roof anatomy explained.