Unveiling the Critical Role of Thermal Insulation: The Diminishing Marginal Benefit Effect of Insulation Thickness

This study investigates the effects of thickness variations in different layers of building walls on heat transfer. A four-layered wall model, consisting of interior plaster, perforated brick, expanded polystyrene (EPS) insulation material, and cement-based exterior plaster, was analyzed in compliance with the TS825 standard. By systematically increasing the thickness of each layer, the impact on the total heat loss of the wall was evaluated analytically. The results indicate that plaster layers had negligible effects on heat loss, while increasing the thickness of the perforated brick reduced heat loss by up to 11.2%. However, the most significant reductions in heat loss were achieved by increasing the thickness of the EPS insulation layer. Notably, this reduction follows a diminishing marginal benefit pattern, where the initial increases in insulation thickness yield substantial energy savings, but further increases provide progressively smaller benefits. These findings highlight that insulation thickness cannot be the sole consideration in optimizing building energy efficiency. Economic analysis is also essential to determine the optimal insulation thickness, ensuring both energy efficiency and cost-effectiveness. This study provides valuable insights for sustainable building design, particularly for projects with limited budgets.