Effects of dynamic building shadows on outdoor thermal comfort across residential layouts

Building shadows in urban residential areas significantly impact the outdoor thermal comfort. To accurately quantify spatiotemporally varying building shadows, the concept of building shadow geographical ratio (BSGR) has been proposed. But its application still faces two challenges: the lack of systematic comparative analysis for various residential layouts and computational inefficiency that hinders rapid evaluation. To address these, this study examined how shadow heterogeneity affected the thermal environment across different layouts using ENVI-met simulations and field measurements from 37 residential areas in Xiamen, China. Key findings indicate that: (1) Linear layouts show a stronger correlation between building shadows and thermal environment compared to staggered and courtyard layouts, with mean correlation coefficient (r) between BSGR and universal thermal climate index (UTCI) of −0.486, −0.130, and 0.179, respectively. (2) The correlation between building shadows and outdoor thermal comfort is more significant with higher average building height (ABH) or lower building density (BD) in linear layouts. (3) Compared to sky view factor (SVF), BSGR shows a more consistent and significant correlation with UTCI, with a mean r of −0.288 versus 0.139 for SVF, and even its negative correlation ratio reaches 100% in linear layouts. (4) The radius for calculating BSGR (termed RBSGR) should vary by building height category, with the recommended RBSGR ranges for Xiamen’s linear-layout residential areas being 15–20 m (high-rise), 10–15 m (mid-rise), and 5–10 m (low-rise). This study elucidates the differential roles of residential layouts on building shadows and the thermal effects, providing practical insights for residential planning.