Sheathing (roof)
Roof sheathing is a lot more than just flat panels onto which shingles are attached. The roof’s sheathing helps to keep the roof trusses or rafters properly spaced and is the strength that holds the entire roof together. As such, roof sheathing has to be structurally sound and properly spaced to allow for expansion and contraction due to seasonal weather fluctuations. While carpenters have attached sheathing to roof trusses for years with a hammer and nails, a framing nailer makes the job go much faster.

Sheathing (wall)
Exterior wall sheathing works in conjunction with the building envelope in preventing wind and water from entering. It can be either non-structural or structural sheathing. Also known as insulating sheathing, non-structural sheathing is installed on an exterior wall to provide added insulation, and in some cases it acts as a radiant barrier. Non-structural sheathing can be applied directly to the exterior wall framing, where diagonal bracing has been installed. It may also be installed on the interior or exterior side of structural sheathing. There are many types of insulating sheathing offering various R-values. Types include plastic, foam, cellulose fiber, paper faced, and foil faced boards. Insulating sheathing is a lightweight panel that is easily cut with a knife. The panels are attached with large-headed galvanized nails to exterior wall framing. When considering the use of insulating sheathing, combustibility becomes as issue, so be sure to follow the manufacturer’s recommendations for installation.

Description sourced from Buildipedia.com. Images sourced from APA Wood and Buildipedia.