Introduction. Over the past 150 years, Central European cities have transformed into highly technological, increasingly sealed environments shaped by infrastructure, in which buildings have become progressively disconnected from their ecological surroundings. Urban processes that once interacted directly with local soil, groundwater, and vegetation were replaced by hygienic, technical, and planning systems, leading to an urban landscape in which buildings function as biogeochemically isolated volumes: containers that absorb, redirect, and ultimately export material flows almost entirely out of the urban ecosystem. Urban ecology since the 1970s particularly through the work of Herbert Sukopp, Ingo Kowarik, and historians of ecological interest such as Jens Lachmund have demonstrated that cities constitute highly dynamic ecological systems with distinct soils, vegetation assemblages, disturbance regimes, and microclimatic structures (Sukopp; Kowarik; Lachmund). Yet in this research tradition, the building itself, with its internal metabolic processes, infrastructural couplings, and biogeochemical emissions, remains largely unexamined. At the same time, systems-ecological approaches most notably the urban metabolism models of the Brussels School around Paul Duvigneaud have shown that material flows are central drivers of urban form, expansion, and ecological transformation (Duvigneaud). These models show how water, nutrients, and biomass circulate through urban systems, but they typically conceptualize buildings as black-box units rather than as active ecological agents within these flows(Fig.1 & fig. 2). In parallel, work in Urban Political Ecology, including scholars such as Matthew Gandy and Koenraad Danneels, have demonstrated how infrastructures, planning regimes, and socio-technical standards govern the circulation of water, waste, and energy in cities. Yet even in these frameworks, the architectural scale and the building’s role as a site where material flows originate, concentrate, or are neutralized have received limited attention. The history of ecological architecture further shows that although many “green” architectural movements since the 1970s adopted ecological rhetoric, they rarely incorporated actual ecological or biogeochemical processes into the functioning of buildings (Adams; Anker). Instead, modern architecture frequently reinforced the separation of buildings from their soil and hydrological contexts, while hygienic interior logics especially evident in kitchens and bathrooms actively avoid ecological dynamics by commulutating and delocating them. This dissertation therefore investigates how urban buildings can regain their biogeochemical connection to their urban surrounding. The aim is to understand the historical development of their decoupling and, through experimental approaches, to explore how existing urban architecture may be reintegrated into ecological processes. State of research. Since the 1970s, urban ecology has established itself as an independent ecological research discipline, significantly influenced by the Berlin School led by Herbert Sukopp. This school defines urban ecology as the study of urban biocoenoses, biotopes, and ecosystems with their specific location conditions and ecological functions. Sukopp and colleagues showed that, despite intensive urbanization, cities offer diverse and location-specific habitats characterized by mosaic-like biotope structures and independent ecological dynamics. While the Berlin School focused largely on the empirical description of the conditions created by urban processes and their consequences, the Brussels School developed a description of the urban ecology of urban metabolism that recognizes urban material flows as central control variables of urban form and function, but has so far insufficiently considered buildings as biogeochemical actors. In architectural history, ecological approaches have manifested themselves since the 1970s, primarily in the adoption of green rhetoric and energy optimisation, although integration into local soil and water processes is mostly lacking (Lachmund). Urban ecology likewise frequently treats the material-flux isolation of buildings like sealed soils, engineered drainage, and controlled interiors as a given condition rather than an active historical process (Grimm; Evans; Danneels). Against this backdrop, a research gap becomes evident: buildings have rarely been investigated as active units that historically shaped and could again shape their immediate surroundings in a biogeochemical way. Research gap. Despite extensive research on urban ecology, which understands urban spaces as independent ecosystems with diverse biogeochemical processes, the role of buildings as shapers of these ecological material flows remains insufficiently studied. While urban metabolism models highlight the importance of material flows for urban development and infrastructure, the connection between buildings and their direct natural environment is usually assumed to be lost and is not systematically researched. Ecological architectural approaches also focus largely on energy and design aspects without considering buildings as an integral part of urban ecosystem processes and soil-water-material cycles. This dissertation therefore addresses the gap in how urban buildings can regain their biogeochemical connection to urban landscapes and thus be reimagined as living nodes in the urban ecosystem. This research gap is significant from an architectural and urban ecological perspective, as it researches new opportunities for the sustainable design of urban spaces that go beyond energy and material efficiency and place the building itself as an ecological actor at the center. Research objective. The dissertation examines the biogeochemical decoupling process of urban buildings, particularly processes relating to water and biomass, and their urban ecological and architectural spatial consequences. The aim is to trace regulatory and infrastructural causes and describe their architectural consequences in order to examine how these material flows were designed over time and how they influenced the natural environment of urban buildings. The goal is to highlight the ecological potential of these material flows and to develop a theoretical and methodological framework for recoupling urban residential buildings with their natural surrounding. Research question. How have urban domestic ecologies in Hamburg become disconnected from their natural environment since the 19th century? What spatial and ecological potential do existing residential buildings have to restore their coupling to ecological processes? What regulatory, cultural, and technical conditions promote or inhibit such recoupling? Methodology. 1. The history of biogeochemical alienation In the first part I will examine the historical development of the biogeochemical decoupling of urban residential buildings from soil, water, and vegetation, with a particular focus on Hamburg. Through archival studies, historical map comparisons, building code analyses, and the examination of kitchen, bathroom, and the open spaces around buildings, I will reconstruct how this alienation took place spatially, technically, and culturally. The aim of the first part of my thesis is to systematically describe the mechanisms of decoupling and to develop criteria that provide indications of how and where buildings could regain proximity to their natural environment today. 2. Reconciliation: Two experimental case studies The second part examines how urban residential buildings can be biogeochemically reconnected with their immediate surroundings. The focus is on the question of which material flows in particular water and biomass are capable of being reintroduced into urban soils, closing nutrient cycles, and thus creating eutrophic, vegetable sites. While the first part of my research reconstructed the archirtectonich consequences of infrastructural decoupling, the second part pursues a design-empirical approach: experimental methods are applied to two residential buildings in Hamburg that are selected according to criteria that are defined by the research of the first part in order to visualize forms of biogeochemical convergence. In both case studies, the existing soil conditions of the direct surroundings are first surveyed: soil structures, degrees of compaction, permeability, water retention capacity, substrate thickness, organic content, and historical interventions (fillings, sealing). At the same time, an analysis is carried out to determine which material flows from the building could actually enter these soils if they were not drained away by technical systems. These include gray water residues from washing processes, organic waste and fecies. On this basis, approximation experiments are developed that aim to reintegrate them into ecological processes as open soils. The experiments are based on ecological principles of succession: the aim is not to introduce designed vegetation, but to activate self-organised site dynamics that are promoted by increased soil moisture, nutrient input and reduced sealing. All interventions are observed over at least two years in order to document succession processes and changes in material cycles. Accompanying these observations, material cycle and succession diagrams are created based on system ecological methods (e.g., Duvigneaud) in order to visually represent the biogeochemical relationships between the building and the surrounding soil and make them comparable. The experimental case studies are not primarily intended to develop standardizable solutions, rather to identify principles of biogeochemical recoupling: Where can a building become “permeable” again? The aim of this work package is to demonstrate real transformation potential and to use specific locations to show how urban buildings can regain ecological proximity not through decorative greening, but by reactivating their biogeochemical relationship with the ground. Expected impact. This dissertation develops a understanding of urban residential buildings as active biogeochemical actors in the urban ecosystem. By combining a historical analysis of biogeochemical decoupling with experimental approaches for reconnection, the work makes an independent contribution to ecologically oriented architecture and urban research. First, the work provides a theoretical framework that no longer understands buildings as closed technical systems, but as potentially permeable, dynamic interfaces with soil, water, and vegetation processes. This expands existing urban ecology and urban metabolism approaches to include a architectural perspective. Second, the dissertation generates methodological innovations by transferring concepts from ecology such as succession, niche formation, and material flow modeling to built structures. The criteria of ecological recoupling capability, architectural succession diagrams, and architectural biogeochemical flux diagrams in the project offer a set of tools that can be used in both research and planning practice. Third, the work opens up concrete paths for the ecological reintegration of existing buildings that go beyond conventional energy and efficiency strategies. Through the experimental investigation of real buildings, potentials for local feedback of water and biomass flows become visible, opening up new possibilities for climate-adaptive and biodiversity-promoting construction. These include approaches to decentralized retention of rainwater, improvement of small urban soils, and promotion of spontaneous vegetation. Fourth, the dissertation is relevant to current transformation processes by showing how buildings can contribute to mitigating the consequences of urban sealing, reducing heat islands, and relieving urban drainage systems. The findings can be incorporated into strategies for climate adaptation, sponge city principles, and biodiversity-oriented urban land-use planning. Overall, the work contributes to thinking of buildings as integral parts of urban ecosystems and opens up new possibilities for how architecture can contribute to a resilient, biodiverse, and material flow-conscious city.