Research on Microclimate Influencing Factors and Thermal Comfort Improvement Strategies in Old Residential Areas in the Post-Urbanization Stage

China’s urbanization process has entered the stage of mid-to-late transformation and upgrading, with the urbanization and population growth rates having passed the turning point. Urban renewal has become an increasingly important issue, among which the renovation of old residential areas holds enormous potential. The improvement of the living environment is urgent, and enhancing the microclimate to improve the livability and comfort of outdoor residential spaces is a critical factor. This study presents for the first time a quantitative framework for multifactor synergistic optimization by coupling building layout closure and material albedo effects. This paper takes typical old residential areas in Fuyang as an example and uses 3D microclimate simulation software (ENVI-met Version 4.3) to establish a simulation model. It evaluates the microclimate and thermal comfort under different building layouts, green infrastructures, building envelope materials, and various surface materials. The results show that: (1) Regarding building layout, the point-cluster layout generally results in the best improvement of daily cumulative physiological equivalent temperature (PET) values, followed by row-type and enclosed layouts; (2) The optimal solutions for improving the daily average PET value are as follows: using glass as the building envelope material in the point-cluster layout; 100% tree coverage in the row-type layout; and 100% asphalt coverage as the surface material in the point-cluster layout. These three conditions reduce the daily average PET by 3.51 °C, 23.87 °C, and 2.65 °C, respectively; (3) The degree of impact on PET is ranked as: green infrastructure configuration > building layout > building envelope materials > surface materials; (4) When the building layout of the residential area is more enclosed, such as using row-type or enclosed layouts, the order of building envelope materials improving thermal comfort is: brick, concrete, and glass. When the building layout is less enclosed, such as using point-cluster layouts, the order of building envelope materials improving thermal comfort is: glass, brick, and concrete. Therefore, it is concluded that applying point-cluster layout in buildings, using glass as the building envelope material, and having 100% coverage of asphalt pavement as the surface material and 100% coverage of trees can maximize the improvement of the thermal environment of the buildings. The conclusion is applicable to old residential areas in warm temperate semi-humid monsoon climatic zones characterized by high densities (floor area ratios > 2.5) and high rates of hardening of the ground (≥80%), and is particularly instructive for medium-sized urban renewal projects with an urbanization rate between 45% and 60%.