It's undeniable that the renovation of existing buildings is a more environmentally-friendly option than demolition-reconstruction. However, encouraged by economic and financial interests, property developers still opt massively for the construction of new surfaces. This choice raises questions for the development policies of our cities, which have a large stock of office buildings awaiting new occupancy. The challenge is all the greater in monofunctional districts such as the European Quarter in Brussels, where new office projects are still very attractive (both for developers and occupiers), without any overall long-term vision having yet been agreed. The interventions carried out often modify the identity of the site and its original values. This article is based on a case study aimed at estimating the life-cycle greenhouse gas emissions of an office building, as well as the financial and fiscal costs of interventions, considering several renovation and demolition/reconstruction scenarios. Based on the results of this study, the aim is to consider the future of these buildings, taking into account the architectural and societal implications.