Can we design buildings within planetary boundaries? An exploration into using a top-down benchmarking approach for embodied carbon

The way we build, occupy, and dismantle architecture contributes heavily to the global problem of climate change. Accounting for the embodied emissions from buildings is just as important as measuring operational emissions. It’s widely recognised that including Life Cycle Assessment (LCA) during design can inform decisions to reduce emissions. However, it is difficult to complete a LCA during the early stages and to define appropriate targets for achieving a project that is within the planetary boundaries (a concept involving earth system processes). Therefore, there is a need for benchmarks that respond to the scale of design decisions and allocate carbon emission targets for different building elements. To support designers in early decision making, this paper explores how a top-down benchmarking approach can be applied to both the building and elemental levels of LCA results. Functional units are applied using fulltime employee to create a cap. The approach is applied to typical and non-typical building typologies from the same case study, a koala rehabilitation centre in Queensland, Australia. The case study was selected to form a discussion around the application of top-down building and elemental benchmarks in commercial architecture practice and test limitations. The paper asks the question: how can top-down benchmarks best support early design decisions to reduce the environmental impact of a building? The results show that whilst top-down benchmarks are good at connecting building scale benchmarks with a global carbon budget, the sharing principles used to achieve the benchmark limit their application on nontypical building typologies.