Circular Hybrid Façades: Responsive Design of Thermally Efficient 3D Printed Concrete Skins on Reused Concrete Elements

3D concrete printing (3DCP) offers a versatile, flexible approach for producing customisable, project-specific components as one-off solutions. This paper explores the use of 3DCP as a circular retrofit strategy to fabricate thermally optimised facade outer skins for reused concrete elements. This work formulates a computational design-to-fabrication workflow for the development of three-wythe printed elements, assessing printability, material quantities, and 2D numerical simulations in THERM, while maintaining a consistent internal topology for fabrication. The approach is tested by simulating and comparing four variants from a benchmark uniform section to a customised design. Thermal transmittance improved from 0.41 W/(m² ·K) for the base design to 0.29 W/(m²·K) for the custom variable case, using the same amount of printing material. These findings indicate that performance-driven design can deliver meaningful performance upgrades for reuse and suggest the potential of 3DCP as a key enabler technology to facilitate reuse and advance circularity in the built environment.