Among different structural elements, floor elements account for the largest portion of the mass and thus the embodied energy of the structures. Therefore, a viable approach to reduce the embodied energy of buildings may involve replacing the conventional floor systems with alternative low embodied energy floor systems. This paper investigates the potential reductions in the life cycle energy of the steel structures achievable through the adoption of steel-timber composite (STC) elements as floor and shear wall systems. Evaluating the life cycle energy implications of adopting STC elements is especially important due to the trade-off between their positive and negative effects on embodied energy and operating energy, respectively, when compared to alternative conventional elements with a higher thermal mass including concrete and steel elements. The life-cycle energy of four different structures designed for a building is evaluated by accounting for energy use in material extraction and processing, component manufacturing, transportation, construction, operation and end of life phases. Two steel structures with STC and steel-concrete composite floors and concrete shear walls are considered to evaluate the effects of STC floors on the energy-usage footprint. The third structure is designed with STC floor system and CLT shear walls: and the fourth structure is designed as a concrete structure to provide a basis for comparison between energy footprint of steel structures with STC and reinforced concrete structures. The results indicate that when designing the building with a steel structure, adoption of STC floor and shear wall systems resulted in 107.5% decrease in the embodied energy at the expense of only a slight increase in the operating energy. Furthermore, adopting a steel structure with STC floors was found to result in considerable life cycle energy savings, viz. 895 MJ/m(2), when compared with the same building designed with a concrete structure. (C) 2018 Elsevier B.V. All rights reserved.