In this paper, a simulation model is developed to predict the effects of phase change materials (PCMs) with different perforated brick thicknesses on the thermal comfort of heavy structural buildings in a free-floating mode under the hot-dry conditions. According to Egyptian building standards, a room with a floor area of 16m2 and a height of 3m is simulated under Cairo (Egypt) weather conditions. Two PCMs with melting temperatures of 29 and 25C and perforated brick thicknesses of 10, 15, 20, 25, and 30 cm are used and evaluated in terms of the exceeding hours, the time lag, and the decrement factor. The simulation model is validated using data reported in the literature for an outdoor cubicle. The results confirmed that the installed PCM layer into the building envelope saves the building's usable area and reduces the initial cost of construction. When the PCM-29 layer is integrated with a 20 cm thick perforated brick, the maximum exceedance hours are reduced by nearly 620 hours compared to 10 cm brick thickness. Combining the PCM layer with the 10 cm thick perforated brick achieved the same exceeding (approximately 1383) hours as the 20 cm thick base case. Seasonal assessment of PCMs revealed that the best PCM behavior varies according to outdoor temperature fluctuations. PCM-25 produces better indoor operative temperature than PCM-29 in spring and vice versa in summer. As the perforated brick thickness increased from 10 cm to 30 cm, the charging time required to melt 5% PCM-25 increased from 3.5 hours to 22 hours. In addition, when the brick thickness is 15 cm, the maximum time lag difference of the PCM-25 layer is about 7.25h. In summer, PCM is most effective when the thickness of the perforated bricks is 20 cm.