Which of the following is NOT considered a main part of a roof?

The chimney is not considered a main part of a roof structure. A chimney, while it may be an integral part of the roofing system, primarily serves the purpose of venting smoke and gases from fireplaces or heating appliances. The main components of a roof typically include the deck, which is the structural substrate that supports everything above it; flashing, which is used to prevent water intrusion at joints and transitions; and valleys, which are the channels formed where two roof planes meet, directing rainwater and snowmelt off the roof. Each of these components plays a crucial role in the roof's function and integrity, while the chimney, although related, is more of an accessory rather than a main structural element.