Abstract
This paper discusses the potential of improving the sustainability of existing cities and towns through residential use of roof-top additions to buildings. The phenomenon of extending existing buildings by adding floors is not especially novel, there being many examples throughout history. However judging by the limited number of recent cases in most cities, this design typology appears to not have received much attention. Building on top can be shown to provide good ecological performance of individual buildings but also improved functioning of the wider built environment. The aim of the paper is through scholarly argument and international case studies to show to city authorities and the development industry the key benefits of building on top of suitable existing building stock. A hypothetical case study is presented wherein building on top is compared with demolishing the existing building and building anew. Attention is given to sustainability in terms of life-cycle assessment; embodied energy; energy in use; CO2 emissions; building materials and technologies, reduction/avoidance of demolition waste; and, footings/foundations. Wider implications of building-on-top are explored in terms of city infrastructure; city services - water, waste, power, transport; city regulations; and, city expansion. Social, cultural and economic enhancement of the city is discussed in terms of cultural heritage and activity; social behaviour, economic performance; and, public health. Case studies scope across a range of approaches and scales from single residences to medium and high density developments. Together they provide transferable ideas for sustainable higher density residential development.