<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (September 2012) (Learn how and when to remove this template message) </Td> </Tr> <P> 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 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 . </P> <P> 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 400 lb (181.4 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 . </P> <P> The history of the garage door could date back to 450 BC when chariots were stored in gatehouses, but in the U.S. it 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 . </P>

What is the weight of a garage door