Techno-Economic and Environmental Evaluation of Building Retrofit Strategies Toward NZEB Targets in Hot Climatic Contexts

In response to growing energy demands and climate pressure in hot regions, this study presents an integrated techno-economic and environmental assessment of building envelope retrofit strategies aimed at facilitating the transition of existing buildings toward Nearly Zero-Energy Building (NZEB) targets. Three advanced retrofit solutions—radiative coatings (RC), glazing-integrated photovoltaic (GIPV) systems, and solar green roofs—are evaluated using a validated building performance simulation framework across four representative climatic zones in Egypt. The results demonstrate that radiative coatings provide the most favorable economic performance, achieving return on investment (ROI) values between 12.37% and 21.72% and payback periods ranging from 3.5 to 6.2 years. Solar green roofs and GIPV systems deliver substantial reductions in annual electricity consumption and operational CO2 emissions, with their performance strongly influenced by climatic conditions and cooling demand intensity. Solar green roofs achieve ROI values of 5.15–6.54% with payback periods of 11.7–14.9 years, while GIPV systems yield ROI values of 4.0–5.24% and payback periods between 14.6 and 17.1 years. Overall, the findings indicate that climate-adapted envelope retrofit strategies can significantly enhance building energy performance while providing measurable economic and environmental benefits. This study offers a robust, data-driven basis for retrofit prioritization and policy formulation in hot regions.