The building sector faces increasing pressure to reduce both operational energy consumption and embodied carbon emissions while maintaining adequate thermal and mechanical performance of construction materials. In this context, the present study investigates the potential of cement mortar reinforced with esparto fibers as a sustainable building-envelope material capable of improving energy efficiency while valorizing locally available natural resources. An integrated methodology combining microstructural analysis, thermophysical characterization, compressive strength testing, life cycle assessment (LCA), and dynamic building energy simulation was adopted. Microstructural observations revealed the porous and lignocellulosic nature of esparto fibers, promoting the formation of air-filled voids within the cement matrix. The incorporation of 4 wt% esparto fibers reduced bulk density by 15% (from 1768 to 1503 kg/m3) and significantly improved the thermal performance of the mortar. Thermal conductivity decreased from 0.553 to 0.310 W/(m·K) (41.7%), while thermal diffusivity and thermal effusivity were reduced by 33.1% and 28.8%, respectively. In contrast, the effective heat capacity increased, enhancing the thermal inertia of the composite. Although the compressive strength decreased from 38.58 MPa for the reference mortar to 14.90 MPa for the CM + 4% EF composite, the obtained values remain suitable for several non-structural building-envelope applications. The environmental assessment indicated a reduction of approximately 127 kg CO2 per cubic meter compared with conventional mortar. Dynamic simulations performed using DesignBuilder/EnergyPlus under two contrasting Moroccan climates (Marrakech and Ifrane) showed that the optimized wall configuration incorporating the CM + 4% EF composite significantly reduced annual heating and cooling energy demands. Cooling demand in Marrakech decreased from 6953 to 4758 kWh/year, while heating demand in Ifrane was reduced from 7555 to 5090 kWh/year. Overall, the results demonstrate that esparto fiber-reinforced cement mortars can simultaneously improve thermal insulation performance, reduce environmental impact, and contribute to building energy savings. The study highlights the potential of natural fiber-based composites as sustainable and climate-responsive solutions for future low-carbon building envelopes.
