Developing countries like India are witnessing a sharp rise in cooling energy demand due to rapid urbanization, changing climate patterns, population growth, and improved living standards. Among the various strategies proposed to address this growing demand, the integration of phase change materials (PCMs) into buildings for enhanced energy efficiency has gained significant global attention [1–3]. In this study, capric acid, a saturated fatty acid, was encapsulated within a multilayer shell. The PCM shell is comprised of an intermediate layer of nano-reinforced calcium alginate with multi-walled carbon nanotubes (MWCNTs) to facilitate faster heat transfer across shell material. The outermost shell layer is composed of fly ash and water-based polyurethane to prevent moisture ingress and to provide protection against mortar mixing stresses and PCM leakage. Differential scanning calorimetry (DSC) was used to evaluate the latent thermal properties of capric acid. Thermogravimetric analysis (TGA) was conducted to assess the thermal stability of the PCM. The microstructure of the bead system was investigated using optical microscopy (OM) and scanning electron microscopy (SEM). Microscopic analysis demonstrates that the PCM is stored in the core as capsules, separated by very thin calcium alginate sheets. The investigation also exhibits the uniform dispersion of well-sonicated MWCNTs in the intermediate layer of calcium alginate. The outermost layer presents a rough and irregular surface morphology, which is likely to enhance the interlocking with the cement mortar matrix. Moisture absorption through the multilayer shell of the PCM bead system was also evaluated. Additionally, gravimetric analysis was utilised to examine the PCM loading in the multilayer encapsulated PCM bead system. The selected PCM has significant latent heat capacity, which can significantly improve the building's energy performance when incorporated into its envelope.