This paper attempts at defining a novel method for designing integrated building skins taking inspiration from nature, where construction happens as an additive growth process with coherent development of form, structure and performance. The research focuses on the hierarchical structure of bones to challenge the current design paradigms of lightweight architecture. A skin system with highly specific material distribution has been conceived with the use of Additive Manufacturing to efficiently provide structural resistance. A method which encompasses computational design workflow, fabrication experiments and performative assessment of full-scale prototypes produced with Additive Manufacturing is described herein. Algorithms for topology optimization of freeform shapes are employed to determine the material organization as well as a performative matrix for the creation of a custom lattice microstructure defined as Functionally Graded Lattice Structures (FGLS), a system of load-responsive interconnected struts with spatially varying characteristics. Through experiments at different scales the viability of the hierarchical load-bearing envelope is demonstrated as a construction system for free-form lightweight constructions. In conclusion, it is discussed how bio-inspired design strategies contribute significantly to define role-models for catalyzing the potential offered by emerging fabrication technologies in architecture
