Abstract: South East Queensland (SEQ) is Australia’s fastest growing region. The Council of Mayors (SEQ) has identified the strategic potential of medium density development in creating greater diversity and affordability in housing markets, as well as promoting a more compact and sustainable urban form. However, the construction of infill buildings at 4-8 storey scale can present significant challenges in terms of achieving sustainable, liveable outcomes within existing site and financial constraints, as well as integration into extant surrounding neighbourhoods. This paper reports on a design research project commissioned by the Council of Mayors (SEQ) that investigated design strategies for improving the liveability and sustainability of medium density infill development, and sought to provide an evidence base for the benefits and costs of incorporating such strategies. Current market developments representative of a status quo were analysed to provide a benchmark and ensure the strategies are feasible within the constraints of market-led delivery. A series of alternative design models were formulated employing simple but effective changes to current market development approaches to improve liveability and sustainability. Cost-benefit evaluation of construction and life-cycle expenditure against a benchmark was undertaken, revealing the increase in construction costs was negligible, and a reduction in energy consumption of nearly 15% was possible. Further design benefits included enhanced quality of space/liveability, alongside improved shared spaces and impact on the public realm and neighbours. Potential adjustments to current planning and building codes are proposed to provide necessary flexibility. More broadly, the research shows the value of a holistic, design-led process of testing, refining and reinventing development parameters.