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The building construction industry is adapting Additive Manufacturing (AM) and robotic fabrication techniques to, among other efficiency and cost benefits, reduce the lifecycle Green House Gas (GHG) emissions of new buildings. This research aims to fabricate a low- GHG emission façade by encoding environmental performance using a combination of material selection, AM techniques, and bespoke geometry. This paper presents the design methodology, specifically the response to solar radiation (i.e. shading and daylight transmission). The key contribution of this publication is establishing the digital fabrication process of AM facades: beginning with performative parametric design, using empirical Bi-directional Scattering Distribution Function (BSDF) data of AM thermoplastic elements for daylight simulation to assess performance, and finally optimising the topology for a specific context (location and orientation).

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sector accounts for 34% of energy demand and 37% of energy-related CO 2 emissions globally. [2] In buildings, a major portion of the footprint concentrates in the first year of the life cycle and results from embodied emission of material and components. This relative contribution is expected to reach values as high as 50% of the total emissions as energy efficiency in buildings increases. [3] At the moment, despite the continued power sector decarbonization and the adoption of climate-change mitigation policies, buildings remain offtrack to achieve carbon neutrality by 2050. [1] Facades constitute the main building boundary between external and internal environments, controlling the flow of energy and matter inside buildings. For this reason, they considerably impact the environmental conditions of indoor spaces, user satisfaction, and operational efficiency. [4] Therefore, improvements in the performance of building facades are critical to meet most of Net Zero Emissions by 2050 scenario reductions in energy use. [5] To meet the performance requirements prescribed by the building codes, advanced facades systems have been proposed, which can tune their behavior in response to variable boundary conditions [6][7][8] and feature smart materials allowing integration of and switching between multiple functionalities. [9][10][11] Apart from the operational Façades are the primary interface controlling the flow of solar energy in buildings and affecting their energy balance and environmental impact. Recently, large-scale 3D printing (3DP) of translucent polymers has been explored as a technique for fabricating façade components with bespoke properties and functionalities. Transmissivity is essential for building facades, as the response to solar radiation is crucial to obtaining comfort and greatly affects electricity and cooling demands. However, it is still unclear how 3DP parameters affect the optical properties of translucent polymers. This study establishes an experimental procedure to relate the optical properties of PETG components to design and 3DP parameters. It is observed that printing parameters control layer deposition, which governs internal light scattering in the layers and overall light transmission. Moreover, the layer resolution determines angle-dependent properties. It is shown that printing parameters can be tuned to obtain tailored optical properties, from high normal transparency (≈90%) to translucency (≈60%), and with a range of haze levels (≈55-97%). These findings present an opportunity for large-scale 3DP of bespoke façades, which can selectively admit or block solar radiation and provide uniform daylighting of a space. In the context of the building sector decarbonization, such components hold great potential for reducing emissions while ensuring occupant comfort.