Understanding the whole roof system Before calling a roofing pro, make sure you know the lingo. Here are the components of the whole roof system: Deck: The wooden, structural surface of the roof. Drip edge: Material affixed along the edge of the roof to guide water off the eaves. Underlayment: A barrier installed under the shingles to keep the deck dry. Flashing: Material affixed to seal and protect joints, such as where the roof meets the chimney. Shingles: The outermost layer of your roof, which repels water and protects the structure. Soffit: The underside of a roof overhang. Fascia: The horizontal board on the end of your roof’s rafters that may hold the gutters. Vents: Features that allow air to escape the attic and keep your roof dry.