In response to mounting regulatory pressures for energy-efficient buildings, this paper presents a systematic literature review of nano-enhanced phase change materials (NePCMs) tailored for building envelope applications. A total of 99 studies published between 2015 and 2025 were identified through structured searches in Web of Science, Scopus and ScienceDirect, following PRISMA guidelines for transparent study selection and data extraction. Key findings reveal that metal-oxide nanoparticles (CuO, Al2O3, ZnO, TiO2) typically enhance thermal conductivity by 15–60 % at 1–5 wt% loadings, while carbon-based additives (graphene, expanded graphite, MWCNTs) can deliver up to 400 % conductivity improvements at low concentrations (0.5–5 wt%). However, increases in conductive fillers often incur a 3–15 % reduction in latent heat, underscoring the need for balance in composite design. Two-step process of mechanical stirring (500–1000 rpm) followed by ultrasonication (20–40 kHz) has emerged as the dominant dispersion approach that is critical for achieving stable, homogenous NePCMs, yet detailed reporting of processing conditions remains inconsistent. Two primary knowledge gaps were identified: (1) the absence of consensus on optimal nanoparticle type, concentration and dispersion method for building-specific PCM applications and (2) insufficient standardization and documentation of synthesis parameters that hinders reproducibility. To address these gaps, this study recommends future side-by-side experimental comparisons under unified protocols, integrated optimization of concentration and dispersion, rigorous method reporting and scaled-up validation in real building contexts. By implementing these recommendations, it would be possible to accelerate the development of reliable, high-performance NePCMs for next-generation energy-efficient structures.