Nanotechnology is emerging as a transformative force in sustainable construction, advanced material development, and environmental health by enabling nanoscale modifications in building systems. Engineered nanomaterials significantly enhance mechanical performance, thermal insulation, and energy efficiency, contributing to reduced carbon emissions, optimized material utilization, and improved indoor environmental quality. In the post-pandemic context, nanotechnology has further demonstrated its relevance through antimicrobial coatings, photocatalytic surfaces, and nanoparticle-based air filtration technologies aimed at mitigating pathogenic transmission in built environments. However, the production and deployment of nanomaterials present considerable challenges, including high energy consumption, substantial manufacturing costs, and unresolved toxicological and ecotoxicological risks. Documented concerns include inhalation-related respiratory dysfunction, cardiovascular effects, and potential neurotoxicity, necessitating stringent exposure assessments and standardized regulatory oversight. Advances in green synthesis methods and continuous-flow microreactor technologies offer promising alternatives for scalable and environmentally sustainable production. A comprehensive life-cycle assessment is essential to evaluate long-term performance, occupational exposure, and end-of-life scenarios. Interdisciplinary collaboration between materials scientists, toxicologists, and urban health researchers is required to guide the safe integration of nanotechnologies. Embedding circular economy strategies, prioritizing low-impact manufacturing, and establishing harmonized international safety standards will facilitate the responsible application of nanotechnology in the transition toward energy-efficient, health-supportive, and ecologically sustainable urban systems.