Development of plant-waste-based composite insulation systems for reducing heat transfer in building envelopes under hot-arid conditions

Reducing cooling energy demand in buildings located in hot-arid regions requires the development of sustainable and cost-effective thermal insulation materials. This study experimentally investigates the thermal performance of composite insulation boards produced from recycled plant waste and mineral additives, including walnut shells, date cores, jute fabric, clay, and glass crumbs. Thermal conductivity was directly measured using a guarded hot-plate apparatus under controlled boundary conditions, while thermal resistance, transmittance, and insulation efficiency were subsequently calculated based on standard heat-transfer relations. The influence of insulation thickness (1–14 cm) and material composition on heat-transfer behavior was systematically analyzed. The results indicate that clay-based composites exhibit the highest thermal resistance, reaching 0.527 m²·K/W at an optimal thickness of 0.14 m, with a corresponding thermal transmittance as low as 1.89 W/m²·K. Statistical analysis confirms that both material composition and thickness significantly affect thermal performance (p < 0.001), while uncertainty assessment shows relative errors below 6%. Compared with conventional insulation materials, the proposed composites demonstrate competitive thermal performance at substantially lower environmental and economic costs. These findings highlight the potential of plant-waste-based insulation systems as sustainable alternatives for improving building thermal efficiency in hot-arid climates.