An Exterior Bi-Fold Door consists of two equal-size panels that are hinged together across the middle. When raised (via electric motor and a series of cables or straps), the top panel folds out and the bottom folds in and under the top, forming a horizontal "V." This configuration results in less stress on building and door frame than does a single-panel door. Built into the system are various safeguards to prevent the door from accidentally coming down. Among the agricultural building applications of the bi-fold (in addition to farm shop) are supply storage, machinery shed, livestock barn, and Quonset hut.