Brownfield sites are the objects of wide debates, from a political and an academic point of view, at a local as well as at international scale, about the opportunity of the regeneration of these pieces of land to improve urban sustainability. Brownfield development, nevertheless, may often achieve this goal with relatively modest expenses: they are, in fact, more easily transformed and the creation of high quality, spatially integrated, well-connected, mixed-use (for pedestrians, cyclists and cars) high value environments is possible at a low global cost. In this paper a case study, "La Goccia di Bovisa", is presented. This urban wide area, located in Milano, accounts for about 85 hectares, and it has been recently included in the list of the most important Italian National Interest Sites (NISs). The study focuses on the comparison of different construction systems for the construction of a modular residential building located in the area. The aim was to define which is able to meet the best performance in terms of carbon emissions and energy consumption in a life cycle perspective. For each option, four different energy targets were evaluated and for each of those the total amount of primary energy (PE) and carbon emission calculated.