The rapid urban growth in the tropics, while being a problem in itself, leads to urban climate changes which pose additional strains on urban energy supply and human comfort. Primary causes for such urban climate changes are amenable to design interventions: urban geometry (limited sky view), thermal properties of building surfaces, anthropogenic heat and air pollution. The net effect of urban climate changes super-imposed on regional changes in tropical cities is the increasing need for building cooling energy. The urban thermal stress on the already stressful tropical climate is making it nearly intolerable. This paper reports the thermal comfort and urban energy implications of a large-scale housing development in urban Sri Lanka, with the aid of building-and neighbourhood-scale model simulations. A cool thermal environment by built-form and layout manipulation is promoted as the preferred adaptation mechanism for high-density tropical cities. Building energy and thermal comfort implications are also explored.