This research locates the racial frameworks produced by the integration of race and style theory in Gottfried Semper (1803–1879) and Eugene Emmanuel Viollet-le-Duc's (1814–1876) organic conception of style. Each architect-writer established a conception of style that emulated the organic principles of nature: Semper's theory of the Four Elements produced a starting point for the morphological development of ornament in history; and Viollet-le-Duc identified the rational logic of structure in Gothic buildings that emulated the internal organization of the body. Furthermore, each architect also alluded to the generative principles of race theory that were prevalent in the nineteenth-century: Semper's conceptualization of type and degeneration in architecture paralleled the definitions of race types in biology; and Viollet-le-Duc's emulation of ethnographic principles was evident in his narration of the transformation of primitive race types through conquest and intermarriage. In order to explore the implications of Viollet-le-Duc and Semper's mention of race theory, this research maps the generative principles of the race sciences inaugurated in the nineteenth century onto the natural organic models each architect constructed to locate the racial frameworks that were produced in their architectural theories. Viollet-le-Duc and Semper's dual reference of race theory and an organic conception of style permitted the nineteenth-century architect to interpret race as style in the context of the architectural style debates. Using the interpretation of race as style, this study produces a reading of the biological, ethnographic and nationalist paradigms of race that were indexed in three domestic building case studies of the period: Gottfried Semper's 1843 apothecary for his brother Wilhelm in Hamburg; Semper's design of Villa Garbald for Agostino Garbald in Castasegna, Switzerland of 1863; and Viollet-le-Duc's Villa la Vedette of Lausanne, Switzerland of 1875. This interdisciplinary approach to the nineteenth-century style debates in architecture provides a historical framework for reconsidering the historical relationship between race and style in two traditions of twentieth-century modern architecture, structural rationalism and tectonics.