What is the role of the roof decking material (such as plywood or OSB) in a roof system?

• A. It serves as the structural base for the roof covering.
• B. It provides permanent waterproofing.
• C. It functions as the primary insulation.
• D. It dictates the color of shingles.

Answer: (A)

The roof decking serves as the rigid base that the roof covering is fastened to and that transfers loads from the roof into the framing. It provides the stable platform that keeps the roofing system in proper alignment and supports weight from wind, snow, and the roof itself. It is not the waterproofing layer—waterproofing comes from the underlayment, flashing, and the roofing material itself, which must seal around joints and penetrations. It’s not insulation either, since insulation is placed in the attic or between framing members to reduce heat flow. The decking’s color isn’t a factor in beauty or performance; that’s determined by the chosen shingles.