Climatic Adaptability of Transitional Space in Traditional Courtyard Dwellings of Jinhua: A Case Study of the Lu Residence in Dongyang

Amid the combined pressures of global carbon-reduction in architecture and the imperative of cultural heritage conservation, new courtyard-style buildings in hot-summer and cold-winter regions face a dual challenge of reconciling historical morphological constraints with contemporary comfort requirements. At the same time, the prevailing energy-efficiency codes in these regions, emphasizing high airtightness and strong insulation, have revealed shortcomings such as poor indoor air quality and insufficient summer ventilation. This study takes the Lu Residence in Dongyang, Jinhua, Zhejiang Province, as the primary case. It systematically examines the coupling mechanisms between the geometric configurations of transitional space in traditional courtyard dwellings and their environmental physical parameters using field surveys, multi-parameter environmental monitoring, and computer simulations. The results identify the optimal orientations and geometric parameters that balance summer ventilation with winter thermal buffering in hot-summer and cold-winter regions. The primary conclusions of this research are as follows: (1) The optimal orientation for axial buildings lies between 15° west of south and 15° east of south, as well as 30–60° east or west of south, with an angle of 45–60° in relation to the prevailing annual wind direction for all buildings. (2) The optimal height-to-width ratio of the courtyard is less than 1:2.5, while the range of the length-to-width ratio extends from 1:0.5 to 1:0.7. (3) The optimal eave depth varies from 900 to 1500 mm, effectively balancing winter heat retention and summer shading; however, a depth of 2400 mm is primarily advantageous for shading purposes. Furthermore, these findings are applied to the design of a new guesthouse within the conservation area of the Xu Zhen Er Gong Ancestral Hall in Yongkang, establishing a climate–geometry matching mechanism for transitional spaces. The study demonstrates that transitional space can serve as effective passive regulators, offering a scientific and sustainable pathway for the adaptive continuation of traditional courtyard architecture.