This study examines the impact of thermal insulation on thermal comfort and energy consumption in an existing house that did not comply with building regulations. Thermal insulation included adding layers of polystyrene in the ceiling and floor, the areas with the highest heat gain and loss. After renovation, findings demonstrated a 55% reduction in heating energy required for winter. Reduction in air conditioning power was 18% during the summer. Simulations using the DesignBuilder software for the house revealed a 42% and a 17% reduction in the energy needed for heating and cooling. TRNSYS software simulation indicated a 500 kWh average annual energy consumption reduction. Experimental results measurements in two days of summer proved that the indoor temperatures of the house did not exceed 25.1°C and remained stable regardless of changes in external temperatures. Thermal insulation is a promising solution for reducing energy consumption and achieving thermal comfort in buildings.