Impact of Green Roofs and Walls on the Thermal Environment of Pedestrian Heights in Urban Villages

(1) Background: Urban villages in Guangzhou are high-density communities with challenging outdoor thermal environments, which significantly impact residents’ thermal comfort. Addressing these issues is crucial for improving the quality of life and mitigating heat stress in such environments. (2) Methods: This study utilized a validated ENVI-met microclimate model to explore the synergistic cooling effects of roof greening and facade greening. Three greening types—total greening, facade greening, and roof greening—were analyzed for their impacts on air temperature, mean radiant temperature, and physiologically equivalent temperature (PET) at a pedestrian height of 1.5 m under varying green coverage scenarios. (3) Results: The findings showed that total greening exhibited the greatest cooling potential, especially under high coverage (≥50%), reducing PET by approximately 2.5 °C, from 53.5 °C to 51.0 °C, during midday, and shifting the heat stress level from “extreme heat stress” to “strong heat stress”. Facade greening reduced PET by about 1.5 °C, while roof greening had a limited effect, reducing PET by 1.0 °C. Furthermore, under coverage exceeding 75%, total greening achieved maximum reductions of 3.0 °C in mean radiant temperature and 1.2 °C in air temperature. (4) Conclusions: This study provides scientific evidence supporting total greening as the most effective strategy for mitigating heat stress and improving thermal comfort in high-density urban villages, offering practical insights for optimizing green infrastructure.