In today’s building construction tenderings, ecological aspects are often taken into consideration. Therefore, it is of vital importance that all stakeholders – architects, structural engineers, owners, constructors etc. –, have an idea on the eco-balance of different construction methods, in order to choose the one being the most appropriate for the tendered project, also in view of building labels. Nowadays, the most widely used construction material for mid-size buildings, such as multi-storey office buildings or schools, is reinforced concrete. Regrettably, concrete requires much energy for production and transportation, strongly draws upon non-renewable resources, and is rather challenging to recycle. Therefore, alternative construction methods are required and to be assessed with regard to their eco-balance. Construction with timber-concrete composite (TCC) elements allows significant reduction of concrete quantities while providing comparable serviceability performance. To provide first insight on the ecological performance of different construction methods, this paper shows case study results of a Life Cycle Assessment for a typical building floor slab. It compares several construction methods, i.e. a traditional reinforced concrete slab, TCC structures as well as a pure timber structure. Traditionally, composite action in TCC elements is provided by mechanical interface connectors (screws, dowels etc.), the latter being habitually designed with elasticity-based approaches. Recently, a new type of shear connection has been developed at the University of Applied Sciences Fribourg omitting the use of mechanical connectors. The new connector shows very stiff and extremely ductile behaviour, principally allowing the application of plasticity-based structural design methods. Based on this observation, the paper further analyses the impact of the applied structural design approach – traditional elasticity-based or more sophisticated plasticity-based approaches – on the eco-balance of the floor slab. It concludes by giving an outlook on the most important elements and concerned stakeholders for improving the eco-balance of typical mid-size buildings.