The UK faces a pressing need for affordable and sustainable housing solutions, as well as a commitment to reduce its carbon emissions. To address these challenges, this project proposes a novel, hybrid lightweight steel framing (LSF) system that can achieve significant material savings and lower environmental impact compared to conventional construction methods. Optimal design and performance of the LSF system, which combines semi-rigid floor-to-wall connections and braced walls, will be investigated using a strain limit design method and an integrated optimization framework. Physical testing and numerical modelling will be conducted, along with cost and sustainability analysis to demonstrate the feasibility and benefits of the LSF system for economic multi-storey mass housing.Â