What is sheathing?

• A. A decorative exterior siding material
• B. Structural covering, often made of plywood or OSB, placed over a building frame's exterior wall studs or roof rafters
• C. A type of insulation used between stud cavities
• D. A finishing plaster applied to interior walls

Answer: (B)

Sheathing is the structural layer placed over the building’s exterior frame—over the wall studs or roof rafters. It’s typically plywood or OSB and acts as a rigid shell that ties the framing together, provides a solid surface to attach the exterior finish, and helps resist wind and other loads. It also serves as a backing for the weather barrier and adds stiffness to the wall or roof assembly. The exterior siding is applied on top of the sheathing, insulation sits in the cavities between studs, and interior plaster or drywall goes on the inside.