Integration of phase change material (PCM) in walls and roof of a building is done to augment human comfort at places where variation of local diurnal temperature of ambient air is extensive. An exhaustive tool to study on year-round thermal effect due to solar radiation falling on a building is generally required to identify the correct PCM and the portion of a year that warrants better thermal management. The transient behavior associated with PCM heat transfer through building roof and walls vary in accordance with location and orientation of the building and the prevailing seasons. Hence, it becomes necessary to carry out a detailed analysis with the integration of PCM layers and to collect information with suitable theoretical approach as experimental study on energy performance of a building is time-consuming and expensive. In this paper, a 3-D building model has been developed and analyzed using ANSYS FLUENT for performing CFD analysis for comparing two identical buildings with and without PCM located at Chennai. The PCM was integrated in roof and walls of the building and analysis was carried out for different days of the year. A novel concept of PCM effectiveness index is introduced to measure the thermal performance due to PCM integration in building. This novel concept is useful for building engineers to measure the effectiveness of PCM integration and to select the correct PCM for thermal management in buildings at any location and time of the year.