Façade design has significant effects on inner conditions of spaces and also on the energy needs to achieve user’s comfort. In this regard, the proportion of glazed surfaces to opaque ones plays a key role. Although the link between the fenestration ratio and energy demand for a space has been widely addressed in literature, a considerable number of these studies were based on isolated models, disregarding the effect of the urban surroundings. The aim of this paper is to provide insights on the impact of the window-to-wall ratio (WWR) on thermal energy demands taking into consideration a specific urban context. The Eixample district of Barcelona, with Mediterranean temperate climate, has been selected as the case study. Heating and cooling energy needs have been evaluated for a single residential space by means of computer simulations in Design Builder for different positions within the tissue. Results show that, from a thermal point of view, the design of façade openings within an urban context should vary depending on the orientation and the degree of obstruction, as a reflection of the differences in energy balance within the building envelope.