What does the roof structure primarily consist of?

The correct answer focuses on rafters and trusses, which are fundamental components of the roof structure. Rafters are sloped beams that support the roof covering and help to create the roof's shape. They provide the necessary support for the roof, enabling it to withstand various loads, such as snow, wind, and rain. Trusses, on the other hand, are engineered structures that consist of triangular units, allowing for greater spans without the need for intermediate supports. They distribute weight efficiently and can be designed to fit different roofing styles and loads.

While the other options include elements related to roofing, they do not comprise the primary structural components of a roof. Sheathing and flashing play roles in protecting and sealing the roof, but they are applied over the framing and do not provide the foundational support. Likewise, roof covering and drainage are critical for weatherproofing and water management, but they do not form the structure itself. Insulation and ventilation are essential for energy efficiency and air circulation, yet they are not structural elements of the roof. Understanding this distinction helps clarify the essential role that rafters and trusses play in roofing systems.