Designers are faced with many options on material and technical solutions during the design phase of the building. Different studies proposing solutions and guidelines are presented in the literature. They help to guide the building project toward low CO2-eq solutions. Despite all these studies, the influence of building dimensions on embodied environmental impacts hasn’t been treated. The dimensions are the first parameters to be defined in the early design phase and can have significant influence in building’s impacts. In this study, we aim to introduce the relationship between the dimensions of the building and their influence in its embodied environmental impacts. Here we limit our study in the case of buildings with structure in cementitious materials, to derive some general principles for design. To do so first, we have assessed the environmental impacts of a single room by progressing its span. Secondly, the impacts have been assessed by multiplying the room in length, width and then in height, by transforming it into a building. Thirdly, we addressed the problem of defining optimal dimensions of a building and construction from an environmental point of view. Finally, the environmental impacts of two different structures, reinforced concrete beam-columns and shear-walls have been compared. According to the type of construction considered, earthquake forces and dimensions in plan and height the study identified the progression of the environmental impacts and the definition of optimal dimensions of the buildings. A good definition of dimensions can reduce significantly the embodied impacts of the buildings. However, further work is necessary for better identifying the optimal dimensions of building by adding to this work the impacts of operation phase
