Experimental and numerical studies of sustainable sandwich bio-composites were presented. The bio-composites were developed using plant-based materials. The laminated face sheets comprised woven hemp fabric and a tree sap–based epoxy, while the core comprised castor oil-based polyurethane foam reinforced with waste rice hulls ashes. Uniaxial compression, tension, and three-point flexural bending tests were performed. Finite element models were developed. Good agreements between experimental and numerically simulated flexural responses were found. From numerical simulation results, the sandwich bio-composites were found to be a structurally acceptable replacement for standard gypsum drywall. Further experimental works are needed to validate the applications.