In the context of a low environmental impact energy mix, the embodied energy of building materials can account for up to 46% of a building’s life cycle energy over a 50-year service life. Fifty percent of this energy corresponds to the combination of the structure and building envelope. While most studies have compared different residential building systems or wall assemblies, this study aims to quantify the contribution of initial embodied impacts to the environmental impacts of wall assemblies’ life cycle for the exterior walls of an office building in Quebec City (Canada). Cradle-to-grave life cycle assessments were conducted on eight wall assemblies, three of which use light-frame construction, one lightweight steel framing, two cross-laminated timber and two glued-laminated timber in a post and beam approach. The life cycle impacts were evaluated using openLCA, the ecoinvent database and the TRACI method. Energy consumption during the use stage was simulated using EnergyPlus. The results indicate that initial embodied impacts can account for 40% to 66% of all environmental impacts throughout the wall assemblies’ life cycle. These results suggest that, in this specific context, the initial embodied impacts can become the dominant source of environmental impacts in wall assemblies’ life cycle. Many factors have been identified as affecting initial embodied impacts such as the choice, the quantity and the nature of materials. The results of this study will help decision makers to identify where efforts should be made to reduce a building’s environmental impacts in similar context.