• nZEB retrofits make embodied carbon the main factor at 94% of whole-life emissions. • A new index for embodied carbon capital gains monetizes carbon in life-cycle costs. • Monetizing carbon through a new index significantly alters optimal design rankings. • The grid decarbonization paradox limits the ability of solar panels to offset carbon. • Deep renovation is cost-optimal, while partial retrofits remain highly inefficient. The recent EPBD 2024/1275 directive mandates a transition from nearly zero energy building to Zero Emission Building standards, shifting the focus from operational energy to the Whole Life Carbon (WLC) footprint. This change elevates the importance of embodied carbon, which often becomes the dominant emission source in high-performance buildings. This paper addresses this new challenge by developing and applying an integrated methodology—combining energy analysis, Life Cycle Assessment, and Life Cycle Cost (LCC) analysis—to a residential renovation in Italy. The core novelty is a new methodology to monetize embodied carbon, integrating it directly into the LCC analysis through a new index, the CG embodied . Results show that while deep renovation eliminates operational emissions (>95%), it increases embodied carbon (+32.6%). While traditional LCC confirms the economic sustainability of renovation, the inclusion of our monetized CG embodied index fundamentally changes the ranking of optimal design solutions, aligning economic viability with WLC decarbonization goals. Furthermore, the study identifies a “grid decarbonisation paradox”: as the electricity grid becomes cleaner, the ability of photovoltaics to offset embodied carbon diminishes. This framework provides a critical tool for designing cost-optimal and truly decarbonized buildings in the zero emission building era, demonstrating that partial interventions are insufficient
Masi et al. (Wed,) studied this question.