The underlayment beneath floors, roofs, and exterior siding.Common in residential construction, wood sheathing like OSB or plywood provides structural strength and a nailing surface for siding and floors. Glass mat sheathing is common in commercial construction. Cement board features a glass fiber mesh for heat resistance, making it ideal for masonry or tile. Non-structural sheathing (foam, foil-faced boards, and plastic) is used primarily for insulation and weather-proofing.
