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.
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 an unequal parallelogram-style hinge lifting mechanism. Newer versions of overhead garage doors are now generally built from several panels hinged together that roll along with a system of tracks guided by rollers. The weight of the door maybe 400 lb (180 kg) 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.
