Abstract Fatty acids-based phase change material (PCM) was supported by graphite interconnected nanosheets to form a shape-stable nano-PCM composite, which complements high heat storage capacity with desired shape-stability, long-term durability, and thermal conductivity. The nano-PCM was incorporated into the gypsum wallboard using a sandwich structure, and the thermal performance of the gypsum wallboards incorporated with nano-PCM was evaluated using test cells under simulated day and night temperature change, in comparison with commercial drywall panels. Use of nano-PCM in wallboards enabled (i) reduction of the interior temperature fluctuations, and (ii) shifted (delayed) the time at which the peak temperature was reached. A numerical model was employed to investigate the contribution of nano-PCM to energy efficiency of the tests cells (representing a scaled, simplified building). Incorporation of nano-PCM into wallboards was found to reduce the energy consumption for maintaining the interior temperature within comfort zone by 79%.