Commercial architecture (fl. 1890-1930), also Commercial Style or Commercial Vernacular, is a style related to the Chicago-specific Chicago School movement, which designed buildings that expressed their steel frame on the curtain-wall exterior. This blog specifically uses Commercial style for smaller-scale buildings and those outside Chicago, while Chicago School architecture must either be in Chicago or be an exact match of buildings there. (A lot of sources cite Beaux-Arts/Romanesque Revival early skyscrapers outside Chicago as "Chicago School," which bugs me.)
The development of the steel frame and other innovations in skyscraper construction benefited smaller-scale designs, too. Interiors could be more flexible, and the storefront of "picture windows" became possible. Many commercial buildings that make up the "Main Street" typology of smaller towns are designed in the Commercial style. Since this is a more vernacular movement and buildings were designed by lesser-known or anonymous architects, it is difficult to trace a more exact history.
Later Commercial style designs include warehouses and early building typologies relating to the automobile, such as garages, repair shops, and dealerships. The style was practiced into the 1920s and was gradually supplanted by Art Deco and Art Moderne architecture for commercial buildings.
Commercial style buildings are short and rectangular, often one to four stories in height. The exterior is usually masonry or brick, which may be supported by an interior steel frame. They have a smaller-scale expression of "base-shaft-capital" with picture windows or storefronts on the ground floor, a regular and unornamented shafted above, and usually a crowning cornice or a parapet on less decorated and later examples. "Chicago windows" are common, a central fixed pane surrounded by two double-hung windows.