Energy and Economic Analysis of Optimum Insulation Thickness for Exterior Walls in Sakarya Province

In this study, the effects of thermal insulation thickness applied to the exterior walls of residential buildings on energy consumption and economic performance were investigated under the climatic conditions of Sakarya Province. The analyses were conducted in accordance with the TS 825 standard. Annual heating and cooling energy demands were calculated using average heating degree-day (HDD) and cooling degree-day (CDD) values for the 2015–2024 period to represent long-term climatic conditions. The overall heat transfer coefficient (U), annual energy demand, life cycle cost (LCC), optimum insulation thickness, and payback period were determined for different insulation materials and insulation thicknesses. The economic analysis incorporated insulation investment cost, energy cost, interest and inflation rates, and fuel price sensitivity over a ten-year analysis period. Increasing insulation thickness significantly reduced annual energy demand; however, the additional energy savings gradually diminished beyond the optimum thickness. Depending on the insulation material, the economically optimum insulation thickness ranged from 6 to 8 cm, while higher fuel prices shifted the optimum thickness toward greater values. The results provide practical guidance for determining economically optimum insulation thicknesses and improving energy-efficient building design in regions with climatic conditions similar to those of Sakarya Province.