The building sector faces growing pressure to reduce total energy consumption across the entire life cycle of buildings. While previous research has predominantly focused on operational energy reduction, increasing evidence shows that structural embodied energy plays a critical role in determining long-term energy performance, particularly under uncertain conditions. This study develops an uncertainty-aware, decision-oriented life cycle energy framework that integrates structural embodied energy and operational energy to evaluate their combined impact on total building energy demand. A set of alternative structural material scenarios is assessed using life cycle energy analysis, incorporating variability in operational energy demand and building service life. The results reveal that embodied energy dominates total life cycle energy during early service periods, while operational energy becomes decisive only beyond specific threshold conditions. Importantly, uncertainty significantly alters comparative performance, challenging deterministic rankings of structural solutions. The findings demonstrate that no single structural system is universally optimal and that robust, moderate embodied energy strategies offer more resilient performance across uncertain futures. The study provides a practical analytical foundation for energy-conscious structural decision-making in early-stage building design.