Mitigating the environmental impacts of building construction is currently a key area of applied Life Cycle Assessment (LCA) research and is receiving increasing attention from European regulatory bodies. This paper presents the results of the upfront carbon footprint calculation for a mid-rise residential building with 7 stories above ground and 2 basement levels, using 906 technically feasible structural design variants. The aim was to determine the range of upfront carbon emissions across viable construction solutions and identify the improvement potential achievable with low-carbon materials and structural systems. The novelty of this approach lies in its independence from heterogeneous data derived from the existing building stock and from the limitations of predefined variant sets generated by design software. Instead, the method aims to cover the entire design spectrum by generating variants with consistent technical parameters and a shared LCA scope. The analysis is based on the statistical evaluation of a comprehensive database of technically equivalent virtual buildings assembled from construction methods typical in current practice. The results indicate that purely timber frame or CLT structures exhibit approximately 17% lower upfront carbon emissions compared to RC or hybrid RC-timber solutions. Among the materials analyzed, only the carbon intensity of concrete was found to significantly influence the total upfront carbon emissions at the building level.