Sheathing is the layer of boards or panels attached to the exterior of a building's structural framing, providing a base for siding and adding structural rigidity. Common sheathing materials include plywood, oriented strand board (OSB), and rigid foam panels. Sheathing creates a continuous surface over wall studs and roof rafters, allowing attachment of weather barriers and exterior finishes. It strengthens the building by resisting racking (twisting) forces from wind or earthquakes. Building codes specify sheathing requirements based on structural needs, climate, and building type. Inspectors verify proper sheathing installation before exterior finishes are applied.