Concrete roof systems have three basic advantages over competitive materials- esthetic appeal, structural economy and functional utility. Double-tees are the most widely used prestressed concrete product in the minimum-span range. Double-tees may be used for many types of buildings. They are very economical, readily available, easily shipped and erected and contribute to early building occupancy. Troffers formed by the stems may be used for air ducts or lighting systems. Hollow-core slabs provide minimum depth with a flush ceiling. They are available as custom precast concrete products or are sold under several trade names. Since their production is highly industrialized, their cost is low. Single-tees are the giants of the precast, prestressed concrete industry. They are used to provide spans ranging from 30 to 100 feet. Longer spans are practical with special design considerations or cantilevered ends. Flange widths range from 4 to 10 feet, although the 8 foot wide section is the most commonly used. Depths range from 12 to more than 36 inches. Attractive and economical roof decks can be formed by using prestressed concrete joists in combination with prestressed planks. The keystone joist may be obtained in depths of 6 to 18 inches and the tee joists in depths of 8 to 20 inches. Joists may be handled with light equipment and they work well with bearing wall construction. Joist and plank construction provides an attractive finished ceiling with excellent acoustical qualities and lighting efficiency.