Lightweight steel-framed (LSF) structural elements in building construction provide a way of increasing building sustainability. These structural elements present great potential for recycling and reuse, allowing the conservation of natural resources and the environment. When compared with other materials, these construction components also provide other advantages: reduced weight with simultaneous high mechanical strength; easier prefabrication, allowing modular elements and higher quality control; shorter periods for assembling the building on-site; no dimensional variations caused by moisture; and low cost. The high thermal conductivity of steel could be a drawback, leading to thermal bridges if not well designed and executed. In the case of LSF components (e.g. walls and slabs) it is necessary to take special care with the elements’ design optimisation, with it being essential to use continuous thermal insulation. The building envelope thermal performance is crucial to provide good thermal behaviour and energy efficiency, allowing a reduction of operational energy. In this paper, the LSF construction system is analysed in order to show its main advantages and drawbacks. The assessment of embodied and operational energy is essential to perform a life cycle analysis. The reduction of both energies’ consumption is crucial to increase the sustainability label. Special focus will be given to the mitigation strategies of operational energy in LSF construction.