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Building energy consumption constitutes approximately 40% of total energy usage in the US. zero energy buildings (ZEBs) have received much attention in the last decade as they can alleviate some of the negative impacts that buildings have on the environment. New materials and systems are emerging that can help regulate building enclosure heat losses and gains in a passive manner, possibly leading to more cost effective ZEBs. A novel thermo-optically responsive solid–solid phase change material (SS-PCM) coating has been developed to help offset heat gains or losses in building enclosures. The study investigates the optical and thermal processes of the SS-PCM, as well as the synergies among different layers within the enclosure system, through a series of numerical simulations. The impacts of the solar incoming angle and phase transition temperature on the absorptivity of the SS-PCM, which have a significant influence on the optical and thermal transfer processes, are explored. The feasibility and benefits of using the SS-PCM system in building enclosures under both warm and cold climates are investigated. Simulation results: (1) confirm the potential of the SS-PCM coatings to reduce undesirable heat exchange through building enclosure in all orientations and identify the roof as the preferred location of installing the SS-PCM system; (2) substantiate the thermal benefits of the system throughout the year and determine the optimal phase transition temperature of the SS-PCM with maximal energy saving; and (3) demonstrate more thermal benefits and energy saving of the SS-PCM coatings in warm climates compared to cold climates, which has been a challenge for most of existing passive solar facades.