High-throughput assessment of Himalayan eco-materials for sustainable green roofing: thermal insulation and advanced material characterization

This study investigates the potential of indigenous tree barks, Olea europaea, Quercus palmeri, Cedrus deodar and Pinus roxburgii, as eco-friendly thermal insulation materials for green roofs, focusing on their thermal properties, water retention capacities and safety profiles. The analysis revealed significant variations among the samples: O. europaea demonstrated a z-average particle size of 516.8 nm and exhibited thermal performance through peaks indicating varying particle distribution. Q. palmeri had a lower z-average size of 451.7 nm, emphasizing its potential for enhanced thermal insulation due to its smaller size and varied structural properties identified through SEM analysis. C. deodar, with a higher average of 633.2 nm, displayed unique microarchitectural characteristics that may contribute to its insulation capability. In contrast, P. roxburgii showed the largest z-average size of 2658 nm, suggesting potential advantages in thermal resistance due to its structural configuration. With regard to heavy metal content, EDS analysis was crucial in assessing environmental safety, with O. europaea revealing significant levels of arsenic (40.09 wt%) and mercury (56.07 wt%), which raise concerns about its suitability for insulation applications. In contrast, Q. palmeri showed an alarming presence of mercury (67.18 wt%) but no detectable cadmium, while C. deodar primarily contained chromium (26.83 wt%) and mercury (73.17 wt%). Notably, P. roxburgii indicated a very high mercury content (99.57 wt%), necessitating careful consideration before use. While these findings highlight the potential of bark powders for insulation, their high heavy metal content presently limits safe direct application. Therefore, future work should address safe processing, mitigation strategies, and long-term durability testing before practical adoption.