What is the term for the first layer of a roofing system?

The term for the first layer of a roofing system is the deck. The deck serves as the structural base upon which the rest of the roofing system is built. It provides support and stability, typically made from materials like plywood, oriented strand board, or concrete, depending on the building's construction. The deck is critical because it must withstand various loads, including the weight of additional roofing materials, environmental factors, such as snow and wind, and any operational loads.

Understanding the deck's role is essential in roofing applications since it directly impacts the performance and longevity of the entire roofing system. Insulation, membrane, and underlayment are important components, but they are layered on top of the deck to enhance energy efficiency, waterproofing, or protection against moisture, respectively. Therefore, recognizing the deck as the foundational layer is vital for a comprehensive understanding of roofing systems.