The overall reduction in the environmental impacts of the construction industry is a complex process that requires methodological and applicative studies on the evaluation of the sustainability of the life cycle, related to both individual product and of the building system as a whole. In this context, with reference to the end-of-life phase of the building, the management of the disassembly and selective demolition plan of the building, allowing the reuse or recycling of the materials as well as of the building components and prefabricated elements used is fundamental. This research aimed to develop a methodology, applied to timber building systems, to mitigate CO2e emissions during the decommissioning and disposal of the building. The quantitative model developed considers the rates of the CO2e emissions involved in C (end-of-life) and D (benefits and loads beyond the system boundary) phases of building sustainability assessment. The model was applied to two wooden buildings: one with an XLAM structure and another one with a framed structure. In both cases, from the perspective of reusing the wood components for a subsequent life cycle, C and D phases of the process achieved an overall negative CO2e emission rate thanks to the offsetting from the carbon storage property of wood. This research has thus demonstrated the possibility of making the wood construction process circular through a zero-emission approach.