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Three trends that occurred in the 1870s are exemplified in the design of the Penn house. The first of these was the increased use of details derived from the French Second Empire style, particularly the mansard roof. The second was the desire to emphasize the vertical, whether in interior space, in volumes, or in detailing. The third was the treatment of ornamental detail in a brittle, angular fashion. Many of the principal features of the Penn house are Italianate—the bracketed eaves, the angular bay windows, and the wood pillared porches with segmental arches. But these elements are here dominated by one single feature, a mansard roof with a concave surface broken by numerous dormers and chimneys.