Subsequent to Cerdà’s well-known expansion plan for Barcelona, the most important urban growth explosion of the city takes place in the mid-twentieth century. Contrary to what many people could imagine, more than 70% of Barcelona’s current parish churches were built in the last century. Moreover, most of them were constructed between the 1920’s and the early 1970’s, coinciding with the Modern Movement, and the latter were erected in total accordance to the post-conciliar concepts. Based on a research that aimed to study the impact of parish churches on the urban growth of Barcelona, this paper addresses how twentieth century churches became focal points of new neighbourhoods and how this vast ecclesiastical heritage, which nowadays has a lower intensity of use, can be adaptively re-used in order to stretch its lifespan. In other words, this paper is about the balances and future challenges for Barcelona’s modern sacred heritage. The typo-morphological methodology used to approach the subject is organized on three scales of analysis: ‘city’, ‘urban space’ and ‘building’. It is demonstrated that parish churches have a great impact on all of them. Focusing on the third one, which refers to the ecclesiastical typology, one can conclude that Barcelona has a wide range of valuable modern churches. Concerning Barcelona, the chosen case studies of re-used religious buildings will show how new uses are able to transform their spaces in a very respectful manner maintaining at the same time their structural essence. Modifying a building just by changing the activity it hosts is one of the simplest, most effective and enthusiastic challenges an architect can accept. Linking re-use strategies with post-conciliar churches, which were often conceived to accommodate other functions apart from religious services, can give us some useful guidelines for the future of this built heritage. Overall, these post-conciliar churches can be re-assigned so that they can be once again the focus of the neighbourhood. Because the matter of question is not only about re-using, giving a new purpose or restoring the building itself, but also about taking into account its contiguous urban space.