What are planks or panels forming the substrate of a roof assembly called?

The term used to describe the planks or panels forming the substrate of a roof assembly is "decking." This component serves as the structural base upon which other roofing materials, such as insulation and roofing membranes, are applied. Decking is crucial for providing stability and support to the overall roof system.

In roofing construction, decking is typically made from materials such as plywood or oriented strand board (OSB) and is installed over the structural framing of the roof. Its primary role is to create a flat surface that helps to distribute loads, provide a solid foundation for the roofcover, and ensure proper drainage.

Framing refers to the structural elements that support the building itself, while sheathing is a term most often associated with the layer that provides a surface for other materials to be attached but is not specific to roofs. Roofing encompasses the final layer or cover that protects the building from weather elements but does not refer to the structural components underneath. Hence, decking is the most accurate term for the elements in question.