The structural covering placed directly over framing members which also serves to transfer loads into the rafters. Wood structural panel sheathing is commonly sold and installed in 4’ x 8’ sheets, although longer lengths are available.

OSB Sheathing
Oriented Strand Board—Manufactured from waterproof heat-cured adhesives and rectangularly shaped wood strands that are arranged in cross-oriented layers, similar to plywood. This results in a structural engineered wood panel that shares many of the strength and performance characteristics of plywood. Produced in huge, continuous mats, OSB is a solid panel product of consistent quality with no laps, gaps, or voids.
OSB Sheathing.
Plywood Sheathing
Plywood—Manufactured from thin sheets of cross-laminated veneer and bonded under heat and pressure with strong adhesives. Plywood is also referred to as a wood structural panel.
Plywood Sheathing.