During the last two decades of the 20th century, a variety of roof systems began to compete with traditional built-up roofs (BUR).These newer systems included modified bitumens, single-plies, sprayed polyurethane foam, and metal panels. Green and cool roofs a nd building-integrated photovoltaics have also improved and expanded the choices for roofing. This abundance of materials from whi ch to choose has greatly complicated roof system design. But it has also expanded the options for integrating roofing elements int o the building to support sustainable design, aesthetics, and other project goals. To select, detail and specify the most appropri ate roof system for a project, a general understanding of the available material options and how to consider the roofing choice in the context of all other design objectives is essential.