A garage door is a large door on a garage that opens either manually or by an electric motor (a garage door opener). Garage doors are frequently large enough to accommodate automobiles and other vehicles. Small garage doors may be made in a single panel that tilts up and back across the garage ceiling. Larger doors are usually made in several jointed panels that roll up on tracks across the garage ceiling, or into a roll above the doorway. The operating mechanism is spring-loaded or counterbalanced to offset the weight of the door and reduce the human or motor effort required to operate the door. Less commonly, some garage doors slide or swing horizontally. Doors are made of wood, metal, or fiberglass, and may be insulated to prevent heat loss. Warehouses, bus garages and locomotive sheds have larger versions. Description A typical version of an overhead garage door used in the past would have been built as a one-piece panel. The panel was mounted on each side with unequal parallelogram style hinge lifting mechanism. Newer versions of overhead garage doors are now generally built from several panels hinged together that roll along a system of tracks guided by rollers. The weight of the door may be or more, but is balanced by either a torsion spring system or a pair of extension springs. A remote controlled motorized mechanism for opening garage doors adds convenience, safety, and security. History The history of the garage door could date back to 450 BC when chariots were stored in gatehouses, but in the United States, they arose around the start of the 20th century. As early as 1902, American manufacturers—including Cornell Iron Works—published catalogs featuring a "float over door." Evidence of an upward-lifting garage door can be found in a catalog in 1906. Single panel garage doors Single panel doors are constructed from one monolithic panel. From the closed position a single panel door swings up and overhead with a hinge on each side (known as jamb type hardware) to the fully open position. A disadvantage of monolithic panel doors is that the swing-up arc of the door occurs partially outside the garage. This means a vehicle must stop and park several feet in front of the door to avoid being hit by the garage door when it is opened. Single panel doors can also be installed with (one piece track type hardware) that