The enhancement of energy efficiency stands as a paramount strategy in addressing the challenges arising from escalated energy costs. In residential construction, improving energy efficiency primarily involves implementing thermal insulation to create a favorable internal environment while minimizing energy consumption and carbon emissions. An empirical study investigated the thermal conductivity coefficient of various clay bricks infused with cellulose fibers derived from sugarcane bagasse. These fibers were incorporated into the bricks at different concentrations (5%, 10%, 15%, and 20%). The study measured physical properties such as heat capacities, density, and thermal conductivity coefficients. Using the Design Builder program, simulations assessed thermal loads on walls before and after insulation. Our models demonstrate significant reductions in CO₂ emissions: Model A (5% cellulose fiber content) achieved a noteworthy reduction, with CO₂ emissions decreasing to 196,727.5 kg—a remarkable 44.6% improvement compared to the baseline. Model B (10% cellulose fibers) realized a 49.5% reduction in CO₂ emissions relative to the baseline. Model C (15% cellulose fibers) exhibited a 52.1% reduction. Model D (20% cellulose fibers) notably achieved an impressive 63.3% reduction in CO₂ emissions compared to the baseline. The results demonstrated that introducing heat-insulating material (cellulose fibers) reduced the heat transfer coefficient by 44.7%, leading to a significant 39.1% decrease in electricity consumption for heating, a 1.3% reduction in cooling, and an impressive 63.3% decline in CO₂ emissions. These findings strongly support the widespread adoption of thermal insulation in residential buildings to achieve energy savings, cost reduction, ad environmental conservation.