The turn of the 21st century brought a suddenly increase in environmental awareness. Civilization, for years focused in an anthropogenic point of view, now begins to adapt to its surroundings by acknowledging that it cannot prosper without the latter. Throughout all the fields of human activity, environmental sustainability – the concept of preserving the aspects that surrounds us – is gaining leverage as a factor of decision making processes. Evidently, being engineering one of Mankind’s greatest tools and since, by definition, Civil Engineering is the one destined to ensure civilization’s adaption to its environment, the merging of the concepts appears essential to the promotion of sustainable development. Sustainable design emerges as the solution for the above, adding the notion of green and environmentally-sound to the already multidisciplinary nature of engineering’s projects. However, for this new conceit to prevail, one must provide the tools and the means for it to endure in the short term and prosper in the longer one. Environmental sustainability assessment methods are the environmental research community devised answer to accomplish such feature. In this work, a concept model of a modern building is analysed through the scope of prEN15978, a draft version of the upcoming calculation method, elaborated by CEN/TC350, for assessing the environmental performance of new and existing buildings. The main objectives are to identify the products and processes that, during the entire life cycle of the building, most affect its environmental performance and, consequently, presenting solutions to optimize the second. Hopefully, in the end, the importance of environmental performance assessment, and more generally, that of sustainability applied to a building’s design will be fully rooted in the reader’s mind.