The transition from the Qajar to the Pahlavi era, concurrent with modernization, brought about profound changes in Iran's lifestyle and architectural form of housing. Despite taxonomic studies, the role of lifestyle as the primary driver of structural changes has received less attention. This research, employing a mixed approach (interpretive-historical and case study), examined 10 historic houses in Tehran (5 from each era). The samples were selected using a targeted method, and data were collected through documentary studies, field observations, and maps. Structural features, including the number of entrances and courtyards, stretch, shape pattern, introversion, and extroversion, were analyzed in a comparative table. Qajar houses, with 2 to 6 courtyards, northeast-southwest orientation (aligned with the sun's path), bilateral to quadrilateral shape patterns, and complete introversion, reflect a large family, privacy-focused, internal-external separation, and self-sufficiency. Pahlavi houses, with reduced entrances, smaller courtyards, varied orientations, a trend towards one-sided patterns, and extroversion, represent the shift to a nuclear family, reduced privacy, gradual elimination of internal spaces, and a consumerist lifestyle. The physical transformation of Tehran's housing is dialectically linked to lifestyle changes, including urbanization, family structure shifts, technological advancements, the emergence of new classes, women's role transformation, and consumption pattern changes. Traditional Iranian architecture in this period experienced a break from tradition, and houses transformed from introverted and self-sufficient entities to extroverted and consumer-focused spaces.