dc.description.abstract
Climate change is one of the greatest challenges of our time, posing huge pressure to both the environment, the society, and the economy. The construction industry is responsible for approximately 40% of the global CO2-emissions. In this context, there is an urgent need to rethink the way we build today and in the future. Architects play a pivotal role in this, as they are the ones who define the load bearing structures, building materials, and energy concepts through their designs. Hence, they can effectively make a major contribution to reducing greenhouse gas emissions. New, innovative concepts are required to build in a resource-efficient manner and keep raw materials in closed loops. A promising solution, that could significantly help in this direction, is the re-use of building materials. As cradle-to-cradle and re-use concepts are not yet very well established, this thesis aims at defining the primary principles, challenges and opportunities when it comes to building with re-used materials. In particular, it lays focus on timber-hybrid construction.There are five key influencing factors for building with re-used materials are identified: (1) standards and laws, (2) certifications, (3) the availability of re-use materials, (4) the planning process, and (5) the load bearing structure and construction. Regarding the legal framework, it becomes clear in the course of the thesis that most standards and laws set clear goals for re-use. However, they do not include specific requirements (e.g. minimum percentage of re-use materials applied in the building). They also do not address specific building materials, such as the recognition of testing methods to control the static properties of timber. The legal uncertainty that arises from this, especially in terms of liability and warranty, is a major obstacle for re-use. Looking at certifications (2), these generally have a positive impact on re-use by making a building's circularity transparent and measurable. However, there is room for improvement in terms of simplifying and standardizing evaluation methods and giving more consideration to extending the lifespan of a component through re-use. The availability of secondary materials (3) through digital market places or product manufacturers also poses a significant challenge. It is promising that there are increasingly platforms for secondary materials and building product manufacturers that commit to taking back and re-offering materials. Additionally, growing digitization allows for transparent documentation of installed materials and their assembly. However, at present, the supply in German-speaking countries, including reusable timber products, is not very transparent and insufficient in quantity to construct buildings on a larger scale. Conversely, the lack of availability has a negative impact on the planning process (4). Due to the heterogeneity and limited supply of re-use products, this process is very resource-intensive, complex, and requires expertise in terms of deconstruction, re-use, and so forth. In terms of load bearing structure and construction (5), this work illustrates that timber construction brings very good properties for reuse. These include high strength throughout the entire lifecycle, homogeneous constructions, detachable component connections, and long-term CO2- storage. Furthermore, digitization opens up new potentials in terms of prefabrication and component connections. Especially timber frame construction allows for adapting the structure to the different properties of reused components. While wood is an ideal candidate for re-use from a structural perspective, it becomes clear in the course of this thesis that there are currently some legal, market-related, and planning-related challenges for the re-use of building materials. By establishing re-use in legislation, planning processes, and in the market, it can represent a sustainable concept for resource-efficient construction in the medium term.
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