Most homeowners never think about what’s under their shingles. But when replacement reveals compromised decking, the choice of replacement material affects your roof’s long-term performance.
What Roof Decking Is
Roof decking (sheathing) is the structural panel layer fastened to your rafters that underlayment and shingles attach to. Most Atlanta homes built in the past 30 years have OSB decking.
OSB (Oriented Strand Board)
OSB is the current industry standard for residential roof decking. Made from compressed wood strands with adhesive resin. Less expensive than plywood and performs adequately under normal conditions.
Georgia-specific concern: OSB is more sensitive to prolonged moisture exposure than plywood. When OSB gets wet and dries repeatedly, it swells, delamintaes, and loses structural integrity faster. In Georgia’s climate — high humidity, frequent rain, temperature extremes — OSB that gets exposed to chronic moisture will fail faster.
Standard OSB for new decking during a replacement is fine when the leak issue is resolved and proper underlayment is installed. The problem isn’t OSB itself — it’s OSB in a moisture-compromised situation.
Plywood
Structural plywood has cross-grain construction giving it better dimensional stability in moisture. It swells less, dries more evenly, and handles Georgia’s wet-dry cycles better than OSB.
Plywood costs approximately $8-$12 more per sheet than OSB (a sheet covers 32 sqft). On a typical roof replacement, upgrading adds $400-$800 — modest.
When plywood is worth specifying:
- You’ve had a chronic leak and suspect the decking has seen moisture cycles
- You’re installing metal roofing — metal is more sensitive to decking flatness
- You’re in a particularly humid microclimate
What Your Contractor Should Do
Identify any soft, spongy, or delaminated decking areas during tear-off, call you before replacing damaged sections, and stagger panel joints for structural rigidity. Decking replacement runs $70-$100 per sheet installed — ask for it as a conditional line item in your estimate.