Since the end of the 20th century that the awareness of the human being towards our excessive dependence on natural and energetic resources has triggered the development of several initiatives and concerns focusing on environmental sustainability. This trend is still very current. Taking into consideration the representation that the construction industry has in this excessive dependency, these concerns are immediately directed to this industry. The creation of instruments and means that allow a progress and an encouragement of the development in the market for higher environmental performances has become essential so that this idea survives nowadays and thrives in the long term. Originally developed in the range of products’ impact evaluation, the concept of life cycle analysis has provided the conceptual basis that allowed the development of evaluation methodologies of buildings’ environmental performance.This dissertation approaches the environmental sustainability theme in relation to the construction industry, more specifically, to the buildings’ branch. It consists of an analysis to a conceptual model of a modern building based on the application of the methodology proposed by prEN15978. It is a previous version of the imminent calculation method to be developed and made by CEN/TC350, having as an aim to provide a calculation methodology to evaluate the environmental performance of new or existing buildings. The aim of this analysis is to identify which products and processes associated with the several stages of the building’s life cycle affect the environmental performance the most, proposing solutions that allow to the optimization of the environmental performance by reducing the impacts. The methodology proposed by prEN15978 will also be discussed and criticized by the author.In the reader, this work intends to raise interest in the environmental sustainability theme, oriented to the construction industry, raising awareness to the importance of the environmental performance evaluation in the project of buildings.