The low thermal performance of conventional cement bricks leads to increased cooling load and inadequate indoor comfort, especially in regions with minimal enforcement of energy codes. To address this challenge, this study introduces an innovative lightweight cement brick composed of 75 % popcorn coarse aggregate (PCA) a recycled substitute for natural coarse aggregate, and 50 % phase change material (PCM) embedded within the brick core. The research methodology integrates a two-phase approach combining experimental testing and numerical simulation using EnergyPlus engine. First, two identical test rooms were constructed: one built with conventional bricks and the other with the proposed PCA-PCM composite. Indoor air and surface temperatures were monitored to assess thermal behavior. These experimental results were then used to validate a numerical model developed in EnergyPlus. The validation metrics fell within acceptable limits defined by ASHRAE standards, further confirming the reliability of the model. Following validation, a prototype residential building was developed and simulated under the extreme desert climate of Suez, Egypt, to evaluate the real-world impact of the proposed brick on thermal comfort and energy performance. The experimental results showed that the improved brick contributed to a reduction in indoor temperature of approximately 5.5 degrees C and a delay in peak heat load by approximately 2 h, compared to the reference room. Dynamic simulation of the residential model further revealed annual energy savings between 5 % and 10 %, with the southwestoriented unit achieving the highest thermal performance, an improvement of 63.83 % in thermal comfort indices. These findings demonstrate that the PCA + PCM composite brick significantly enhances thermal comfort and reduces energy consumption in hot-arid climates, offering a sustainable and effective alternative for future energy-efficient construction.