This paper presents a thermal analysis of a building concrete roof with vertical cylindrical holes filled with phase change material (PCM). The objective of incorporating the PCM into the concrete roof is to increase the value of thermal mass of the roof. The PCM absorbs the heat through the melting process before it reaches the indoor space, and thus reducing the heat gain. Numerical method is extensively utilized in this research and it is validated with experimental work. The thermal effectiveness of the proposed concrete roof with PCM is assessed by comparing the heat flux at the indoor surface with that of solid concrete roof during the day. A parametric study is conducted to evaluate the effects of the cylindrical holes dimension, PCM melting temperature, and operating month on the heat gain. The results indicate that heat gain can be reduced significantly with larger PCM holes diameter. The PCM melting temperature of PCM should be selected based on the operating month and working hours for the best performance. For the examine cases in this research, the heat flux at the indoor surface of the roof is reduced between 9% and 17.26%, depending on the selected PCM, working hours, and operating month. (c) 2013 Elsevier B.V. All rights reserved.