The late 19th and early 20th century was a period of transition architecturally, marking the entrance into a new era of building. This was the beginning of forward looking architectural design with styles not based on previous building forms. Changes in construction techniques, especially the development of sky scraper technology, and a desire to create houses that fit visually into the natural environment influenced the developing styles of this era. The first style to emerge from this architectural movement was the Sullivanesque style. Named for its creator Louis Sullivan, a prominent American architect, the Sullivanesque style was developed as a design for sky scrapers. Sullivan divided the sky scraper into three parts, an entry level, midsection, and highly ornamented top cornice. This style shows the influence of the Art Noveau movement in the curvilinear lines and complex patterns of the decorative elements. The Commercial style, sometimes called the Chicago style, is a more pared down design for sky scrapers based on a steel frame construction. Sometimes ornamented with elements of other styles like the Romanesque or Gothic Revival, the basic grid design of the Commercial style is still evident.
The other architectural style innovations of this period occurred in the design of residential structures. American architectural force Frank Lloyd Wright created the Prairie style, desiring to develop a new domestic form that fit naturally into the environment of the Midwestern prairie. Wright, along with other Chicago architects known as the Prairie School, designed houses with gently sloping roofs, deeply overhanging eaves, and horizontal emphasis. Vernacular versions of the Prairie style such as the American Foursquare house are far more common in Pennsylvania than pure examples of the Prairie style.
The Bungalow or Craftsman style is another residential style that developed at the turn of the 20th century and became widespread throughout the country in various vernacular forms. Bungalows were first seen in California and were inspired by the English Arts and Crafts movement stressing hand-crafted materials and harmony with nature. Known for their heavy columned front porches, front facing gables, and overhanging eaves, Bungalow style houses often have exposed rafters and other decorative wood trim as well. Pattern books and mail order catalogs enabled the Bungalow style to become very popular in the developing suburbs of the early 20th century. The styles of this period set the stage for even greater change in architectural theory and practice in the years to follow.