Quel avenir pour les immeubles de bureaux du quartier européen ? Comparaison de plusieurs scénarios : une rénovation en bureaux, une reconversion en logements et une démolition-reconstruction en bureaux ou en logements

Résumé. Du point de vue environnemental, il semble évident que la rénovation des bâtiments existants constitue une issue plus favorable que la démolition-reconstruction. Cependant, encouragés par les intérêts économiques et financiers, la promotion immobilière favorise encore massivement la construction de surfaces neuves. Ce choix pose question pour les politiques de développement de nos villes qui possèdent un important parc d’immeubles de bureaux en attente de nouvelles occupations. L’enjeu est d’autant plus grand dans les quartiers monofonctionnels, comme le quartier européen à Bruxelles où les projets de bureaux neufs sont toujours très attractifs. Ces projets souvent menés sans qu’une vision à long terme n’ait préalablement fait consensus ont, en outre, des impacts conséquents, et parfois irréversibles, sur l’identité du lieu et ses valeurs d’origine. Cet article se base sur une étude de cas visant à estimer les émissions de gaz à effet de serre sur le cycle de vie d’un immeuble de bureaux, ainsi que les coûts financiers et fiscaux des interventions en considérant plusieurs scénarios de rénovation et de démolition-reconstruction. À la lumière des résultats de cette étude, il s’agit d’envisager le devenir de ces immeubles en intégrant dans la réflexion les implications architecturales et sociétales. Abstract. From an environmental point of view, it seems clear that the renovation of existing buildings is a more favourable outcome than demolition-reconstruction. However, encouraged by economic and financial interests, property developers still massively favour the construction of new buildings. 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. These projects, which are often carried out without any long-term vision, also have a significant and sometimes irreversible impact on the identity of the site and its original values. This article is based on a case study aimed at estimating the greenhouse gas emissions over the life cycle of an office building, as well as the financial and fiscal costs of the interventions by considering several renovation and demolition-reconstruction scenarios. In the light of the results of this study, the aim is to consider the future of these buildings, taking into account the architectural and social implications

Office to housing conversion: estimating life cycle environmental and financial performance

Renovating existing building is often touted as having an improved environmental performance as compared to demolition and construction. However, very few studies have quantified the life cycle environmental benefits resulting from such renovations. The aim of this research is to provide a benchmark based on a real and representative case study building to estimate life cycle greenhouse gas emissions and financial costs of redeveloping an office building by considering different scenarios: (1) renovation as an office building; (2) conversion as a residential building; (3) demolition and construction of an office building and (4): demolition and construction of a residential building. Results show that the demolition-construction scenarios are undoubtedly the most environmentally impactful, but the difference between offices and housing is less significant and depends greatly on the assumptions made. On the other hand, from a tax point of view, the demolition-construction scenario is favoured by the real estate industry because it allows for the recovery of VAT in the operation and thus maximizes the value of the real estate asset as well as the financial return. There is also a significant difference between the profitability of a housing and an office project. The latter is favoured by market values. The tendency to favour offices in the European district could be reversed in the current post covid situation and solutions exist to encourage the development of housing projects through office conversion

Halogens in chondritic meteorites and terrestrial accretion

Volatile element delivery and retention played a fundamental role in Earth’s formation and subsequent chemical differentiation. The heavy halogens (Cl, Br and I) are key tracers of accretionary processes due to their high volatility and incompatibility, but have low abundances in most geological and planetary materials. Noble gas proxy isotopes produced during neutron irradiation provide a high sensitivity tool for the determination of heavy halogen abundance. Here we show that Cl, Br and I abundances in carbonaceous, enstatite, Rumuruti and primitive ordinary chondrites have concentrations ~6, ~9 and between 15-37 times lower, respectively, than previously reported and most commonly accepted estimates1. This is independent of the chondrites’ oxidation state or petrological type. Bromine/Cl and I/Cl in all studied chondrites show a limited range, indistinguishable from bulk silicate Earth (BSE) estimates. Our results demonstrate that BSE depletion of halogens relative to primitive meteorites is now consistent with lithophile elements of similar volatility. The new results for carbonaceous chondrites demonstrate that late accretion, constrained to a maximum of 0.5 ± 0.2 % of Earth’s silicate mass2–5, cannot solely account for present-day terrestrial halogen inventories6,7. It is estimated that 80−90% of heavy halogens are concentrated in Earth’s surface reservoirs7,8 and have not undergone the extreme early loss observed in atmosphere-forming elements9. Therefore, in addition to late accretion of halogens and mantle degassing, which is <50% efficient over Earth history10, efficient extraction of halogen-rich fluids6 from the solid Earth during the earliest stages of Earth formation is also required. The hydrophilic nature of the halogens supports this requirement, and is consistent with a volatile/water rich late-stage terrestrial accretion</p