Reductions in energy sources and related costs have led to the need for considering some buildings with optimum performance. In recent decades, there was a lot of research on the effect of phase-change materials on improving the thermal specifications of concrete. In this research, we have tried to investigate the effect of phase-change materials in concrete, gypsum and external walls of buildings as well as the hollow-core ceiling and a fairly realistic room. Using finite element analysis, this simulation has been run by applying the Fluent Software. The simulation has done by using different input variables. Two thicknesses of 10 and 20 cm for walls, one thickness of 21.5 cm for a hollow-core ceiling and one 5 × 3 m room have been considered. In this study, a variety of phase-change materials (PCM) were evaluated and two types of optimized PCM were selected for each of the temperature conditions. Also two types of normal and lightweight concrete as well as a gypsum sample were used. Temperature profiles of a hot day in Kashan, relatively hot in Ardabil, very hot in Ahwaz and cold in Kashan were considered as the ambient temperature. Different thicknesses of PCM and its embedding locations, and also the number of optimum layers were studied. Numerical results show that, the presence of PCM has reduces the temperature fluctuations of the inner surface of walls and ceilings up to about 5 ° C for Kashan and about 11 ° C for Ahwaz. Changes in the thickness of the PCM and walls have a great influence on the internal temperature, and the type of PCM has a significant effect on the storage and transmission of energy. The use of PCM in hollow-core ceilings contributed greatly to energy savings. In the modeling of the fluctuations room, the internal temperature drops about 3 ° C. Key Words Concrete wall, Hollow-core ceiling, Phase change material, Simulation, Finite element, Energy saving