Pushing the Envelope: Generative Design and Optimisation of Light-Framed Building Envelopes Using Circular Economy and Life Cycle Assessment Metrics

The design of building envelopes plays a critical role in determining a building’s environmental impact, operational footprint, overall building performance, and potential for resource reutilisation. The most significant environmental impacts occur at the beginning and end of the building’s life cycle. Conventional building envelope design practices and materials lead to high environmental impacts at the construction stage and limit reuse or recycling at the end-of-life stage, resulting in resource loss. Additionally, common construction materials often contain harmful chemicals and additives damaging to human and environmental health, and inhibit reuse, recycling or disposal. In contrast, biobased, biotic, and recycled materials offer the potential to reduce impacts at the construction stage and enable resource circularity at the end-of-life stage. There is extensive research on building envelope performance (both hygrothermal and environmental) and growing bodies of work on alternative building materials and building envelope optimisation. There are also several investigations on how to assess and quantify the life cycle and circular economy potential of building parts, which can be adapted for assessing building envelopes. However, there is a research gap in integrating these aspects, which seems essential for moving closer towards net-zero environmental impact buildings, especially given the challenges of balancing conflicting environmental objectives across a building’s life cycle. This dissertation argues that the most effective way to reduce the environmental impacts of building envelopes is to apply circular economy principles concurrently to the beginning and end of the building envelope’s life cycle. However, the complex relationships among factors in building envelope design—such as material selection, make-up sequence, assembly, disassembly, and recycling, reuse and disposal—pose limitations. This research proposes a novel design process and tools to balance contradicting environmental and design objectives and arrive at highly optimised design strategies and solutions. The approach has two main steps: (1) Amassing and analysing life cycle assessment data for both common construction materials and biobased, biotic and recycled alternatives. Information is collated into a materials database suitable for integration with computational design tools. (2) An editable and adaptive generative model is created to generate and analyse an extensive range of light-framed building envelope assemblies with constructional and material variations. A multi-objective metaheuristic optimisation algorithm drives the generative model and generates highly optimised wall assemblies for user-defined parameters and objectives. Strategies for achieving low-impact assemblies are investigated by comparing the results from different parameter and objective combinations in a series of comparative investigations. Overall, results show that the best outcomes are achieved when assemblies use, and adapt their construction to accommodate, a high share of dense, ligneous materials. Optimal assemblies tend to balance design complexity to include advantageous component/material combinations while avoiding disadvantageous combinations. The generative model operates as a proof-of-concept and does not incorporate full code compliance, buildability, or hygrothermal validation. Disassembly assessments are model-based and untested against physical construction, and results depend on the quality and completeness of available environmental data. The research proposes a novel design tool, an integrated assessment process, and design strategies for light-framed building envelopes, pursuing a holistic concept of minimising environmental impact. It combines guidance for the use of materials and circular design strategies with robust performance validation—paving the way for environmentally optimised building envelopes.