What thickness should roof decking be?
Short answer. For most Georgia homes with trusses 24 inches apart, roof decking should be at least 7/16 inch OSB or 15/32 to 1/2 inch plywood with a matching span rating, which spans that spacing without depending on edge support. Thicker 19/32 or 5/8 inch panels make a stiffer deck for wider spacing, heavier roofing or extra durability, and repair sheets should match the existing thickness.
Three sets of requirements
- The code: panels must carry a span rating suited to the rafter or truss spacing, with edge support where the table requires it. Georgia enforces the 2024 IRC with state amendments.
- The shingle manufacturer: installation instructions set minimum deck requirements, and warranties can depend on meeting them.
- Good practice: a deck that is flat, firmly nailed and stiff enough not to sag between supports.
What you will find on Georgia homes
- Newer homes: often 7/16 inch OSB on 24 inch trusses, with H-clips between trusses.
- Homes from the 1970s through the 1990s: often 1/2 inch plywood or OSB, and sometimes 3/8 inch plywood.
- Older homes: 1x board decking, sometimes with gaps between boards.
Signs your decking is too thin or weak
- Visible sag between rafters and a wavy roofline.
- A springy feel underfoot.
- Shingles showing ridges at panel edges.
For repairs and replacement
- Match the existing thickness so new and old sheets sit flush.
- Use exposure-rated panels with the right span rating.
- Leave the recommended gap between panels and support unsupported edges.
- Nail to the current schedule.
When to upgrade
Board decking with wide gaps, sagging thin plywood, or a switch to a heavier roofing material can justify new or overlaid sheathing. Discuss it at the inspection, since it changes the scope and price.