What type of material is used to provide a surface for roof insulation?

Plywood is commonly used as a surface for roof insulation because it provides a stable and flat substrate for insulation materials to be applied on top. It acts as a dependable base that supports the insulation layers and contributes to the overall structural integrity of the roof. Plywood is easily worked with, can be quickly installed, and offers several benefits such as resistance to moisture when treated, making it suitable for various roofing systems.

The other materials listed, while they have their own uses in different construction scenarios, are not typically used as a surface for roof insulation. Metal sheets might serve as the final roofing surface or as part of a roof assembly but do not act as a substrate for insulation. Plastic panels are often used in lightweight constructions or for specific types of roofing applications, but do not provide the density and structural support that plywood does. Concrete boards are heavier and more commonly used in wall systems rather than as a surface for insulation in roofing applications.