What is roof sheathing, and how much does it cost?
Short answer. Roof sheathing is the structural layer of wood panels or boards fastened over the rafters or trusses, forming the flat surface the underlayment and roofing attach to. On most Georgia homes it is 7/16 inch OSB or 1/2 inch plywood, and it braces the roof frame against wind as well as holding the nails. Replacement is usually priced per sheet.
What sheathing does
- Nail base. It gives shingle nails something solid to grip.
- Bracing. Nailed panels stiffen the roof frame so it resists racking from wind.
- Load spreading. It carries the weight of roofing, people and debris across the rafters.
Common types
- OSB: the most common panel on newer homes, made of wood strands bonded with resin.
- Plywood: layered veneers, often CDX grade, common on many homes.
- Board decking: solid boards on older homes, sometimes covered with new panels at reroofing.
- Radiant barrier sheathing: OSB with a foil face toward the attic, widely used in the South to reduce attic heat. See attic heat and shingles.
Thickness and spans
Panels carry a span rating stamped on them, which tells how far apart the framing can be. Rafters 24 inches apart typically call for thicker panels or panel clips between rafters.
How replacement is priced
During a roof replacement, damaged sheathing is priced per sheet, so the total depends on how many sheets are bad. Full re-sheathing, such as covering old board decking, is priced as its own line. Ask for the per-sheet price in writing before work starts and photos of what was replaced. The differences between the two common panels are laid out in OSB vs plywood roof decking.