Standing amidst architectural Gothic of an earlier period, the new Hunter College library in New York City is a striking innovation in concrete construction. The roof is entirely made of thin shell concrete. It consists of six structurally independent reversed umbrella shapes, which are key locked at the edges and tied together with dowels to form an overall area 120 feet wide by 180 feet long. The theory behind the umbrella design is that roof loads are transmitted form the thin shell concrete to the stiffener ribs by shear, and carried down the ribs by compression to the central supporting columns. The innovations actually proved highly efficient and yet low in cost for this single story building. For one, its unique design offers an interior relatively free of columns which is not easily achieved at moderate cost by conventional construction methods. Moreover, inherent in the design are several construction economies which made it possible to keep cost within a moderate budget. For one, less concrete was needed for the thin shell roof. Two, labor was saved because the roof did not need finishing. Three, in forming the paraboloid only plywood was needed. Finally, savings were made through the use of prefabricated mats of heavy welded wire fabric fro the reinforcement.