There are four main parts of a roof: the rafters, decking, underlayment, and covering. Rafters are the innermost frames that cover the basic roof structure. The decking boards attach to the rafters and offer a level surface for the roof covering.
The underlayment covers the decking boards to help insulate and protect your home from external factors such as harsh weather conditions. Finally, the roof covering is the outermost layer which can be constructed from a variety of materials such as asphalt shingles, metal, clay, slate, or concrete, to name a few.