Final answer:
Roofers use an underlayment on top of the plywood as a water-resistant barrier to protect from the weather. It's usually made from felt or synthetic materials and is essential for preventing leaks and extending roof life.
Step-by-step explanation:
Roofers roll out an underlayment on top of the plywood to protect it from the weather. The process of installing roofing materials involves several layers for optimal protection and durability. The underlayment acts as a barrier against water and weather elements, providing an extra layer of protection beneath the shingles or other roofing materials.
Typically made from felt or synthetic materials, this water-resistant layer helps to prevent leaks and can extend the life of a roof. While laying out the underlayment, roofers must ensure it is flat and secure to prevent any water from getting underneath, which could cause damage to the roof's structure.