The thermal performance of building walls integrated with phase change materials (PCM) was evaluated in terms of heat flux reduction and heat transfer time delay. To fully melt and solidify over daily cycles, PCMs must be incorporated as thin layers placed longitudinally within the walls. The thin PCM layer was integrated into the wall via a thermal shield, whereby the PCM was contained in thin sealed polymer pouches, arranged in sheets laminated with aluminum foil on both sides. This system is herein referred to as "PCM thermal shield (PCMTS)". The optimal location of the PCMTS within the wall cavities is critical for heat transfer reduction and management. The thermal performance of south and west facing walls with and without PCMTS was evaluated experimentally using two identical test houses. The PCMTS was installed at various depths, one at a time, within the wall cavities. Each location depth was numbered from 1 to 5 starting at next to the wallboard surface facing the wall cavity (location 1) and proceeding to the exterior side of cavity at intervals of 1.27 cm. The results showed that the optimal location for a PCMTS in the south wall was location 3 (2.54 cm from the wallboard), while the optimal location for a PCMTS in the west wall was location 2 (1.27 cm from the wallboard). At these locations, the peak heat flux reductions were 51.3% and 29.7% for the south wall and the west wall, respectively. The maximum peak heat flux time delays were 6.3 h for location 1 in the south wall and 2.3 h for location 2 in the west wall. The maximum daily heat transfer reductions were 27.1% for location 3 in the south wall and 3.6% for location 5 in the west wall. (C) 2014 Elsevier Ltd. All rights reserved.