Abstract This paper presents a design optimization related to the application of phase change materials within buildings, which aims to maximize the utilization of latent heat capacity to improve indoor thermal comfort during summer season. Two performance indicators are developed: efficiency coefficient (a representation of the effective utilization of latent heat storage capacity) and effectiveness coefficient (a representation of improvement of indoor thermal comfort). A series of parameters which influence the efficiency coefficient and effectiveness coefficient are identified and then formulated to quantify those coefficients for optimal design. With the performance indicators defined, a case study is performed in a typical standard Australian residential house to derive the optimized design of PCM refurbishment utilizing the developed performance indicators. Results reveal that the performance indicators are effective in the selection of optimum PCM configurations so that the resultant PCM storage efficiency and indoor thermal comfort are optimized. This is particularly demonstrated by the significant enhancement of storage efficiency and effectiveness of optimized PCM compared to non-optimized cases for each climate conditions. Furthermore, an optimized PCM condition is found to be more cost-effective than the non-optimized conditions.