sheathing

1. A layer of boards or of other wood or fiber materials applied to the outer studs, joists, and rafters of a building to strengthen the structure and serve as a base for an exterior weatherproof cladding.
2. Nautical. An exterior covering on the underwater part of a ship's hull that protects it against marine growths.
3. The act of providing sheathing.

noun

A thin outer covering of an object: lamina, membrane, sheath, skin. See surface/depth.

1. The covering (usually wood boards, plywood, or wallboards) placed over exterior studding or rafters of a building; provides a base for the application of wall or roof cladding. Also see sheeting.
2. In colonial America, boards on the interior of a house that served as an interior surface finish.

diagonal wooden sheathing

The noun has one meaning:

Meaning #1: protective covering consisting, for example, of a layer of boards applied to the studs and joists of a building to strengthen it and serve as a foundation for a weatherproof exterior
  Synonyms: overlay, overlayer