The process of Americanization and change in barn construction actually began soon after initial settlement and was motivated by the problems and opportunities of farm life in the New World. From the earliest settlements, Colonial barn builders began simplifying their barn-building practices, eliminating the complexities of their European medieval traditions by standardizing bay sizes and eliminating complex joint assemblies and oversized structural pieces. These small, continuous refinements in barn making erupted in a great change in barn building during the late nineteenth century and created a watershed division in American barn construction between modern and premodern barn types. The new barn that crystallized this major evolution was the Gambrel (double sloped roof) barn. It was not only the shape of the roof that made it new, but vast changes in the building system separated it from previous barns. The Gambrel roof barn incorporated standardized, lightweight, machine-sawn structural members into an advanced truss configuration with nail construction. Its new roof truss system produced the modern symbol of the technologized barn, the ubiquitous double sloped Gambrel-roofed barn. Today, more than a century after its introduction, it is the most widely accepted symbol for the American barn. For late-twentieth-century Americans, it is difficult to imagine this now familiar symbol of the farm as a once new and revolutionary structure that transformed barn construction -- but that is what it did. The Gambrel barn is the fitting symbol for the American barn, not only because it is so widespread, but because it marks the triumph of the modern technologically advanced Americanized barn.

The Gambrel barn and related barns of the late nineteenth century mark the advent of the standardized construction systems, mass-produced building materials, mail-order planning and distribution, and national barn-building traditions. These vast changes did not happen swiftly but were incrementally applied by individual farmers over long periods of time. Within all periods, new ideas competed with older existing traditions of barn building. For example, even the adoption of a new gambrel roof system with stud walls and a truss roof did not wholly eliminate the old heavy timber mortise-and-tenon construction system. Barn builders frequently integrated both old and new systems into the overall structural framework.

The effects of these modern changes in barn construction are not always apparent because farmers have always maintained previous structures even while building new ones. Today, probably one-half of existing American barns were built before 1920. If the new structures from any period are compared, however, the steady march of progress" is clearly apparent and will nullify any hint of nostalgic appreciation for old-time barns on the part of the farmer. Today, the late-twentieth-century modern barn is a modern agricultural machine (like all new barns were in any period), with a concrete floor, post-frame, premanufactured truss roof structure and metal roof and walls. This new barn represents the third major wave of American barn construction by replacing the gambrel barn, which had previously replaced European barns, as the most common barn type. Functionally, today's modern barn re-establishes the earlier English Colonial tradition of housing separate agricultural activities under different roofs. The late-twentieth-century barn also separates functions such as vehicles, animals, feed, and crops in the latest technologically driven production system. In retrospect, it is clear that the centralizing tendency in barn construction, which was initiated by the Pennsylvania Germans and reached a peak in the late nineteenth century, was gradually replaced in the twentieth century by a specialized agricultural production system with separate barns.

Despite numerous construction and stylistic differences, American barns are most effectively classified by their building usage. Functional classification allows barns to be grouped according to activity: crop storage, animal shelter, vehicle and implement storage, and various combinations of all these activities. In function classification, the major regional distinctions between barns stand out. Perhaps the greatest regional variation in American barns occurs along a north/south axis and is based upon how farmers responded to the severity of the winter. Because animals, and to a lesser extent crops, require less shelter further south and west, barn traditions in the south and west have tended to produce smaller, more specialized barns. In the north, barn builders sought more extensive structures to house crops, animals, and vehicles in the winter. Climatic response to functional needs, more than any other factor, makes the typical barns from the northern regions of America look different from those in the south.

Once regional variations by climate are acknowledged, the most critical factor in the shape and construction of barns on the typical farm is the type and scale of agricultural operation. Every region of America has produced specialized barns for single crops or animals or individual agricultural operations. The tobacco barn, hop barn, cattle (pole) barn, potato barn, tractor barn, apple barn and many regional specialty barns attest to the popularity of single usage barns. Until recently, however, the largest percentage of major barns combined a cycle or range of agricultural activities, such as milking cows and hay storage under one roof. These multifunctional barns, the Pennsylvania bank barn, Midwest feeder barn, and the Wisconsin dairy barn, are the most common pre-1950 barns in America.