In the European Union, building construction accounts for 40% of materials consumption, 40% of overall energy consumption, and 40% of waste production [1]. It is therefore essential to reduce the environmental impact of these structures. Various levers are available to achieve this, including better use of materials and selection of the most appropriate material for a given application. This study focuses on isostatic beams, a simple application for identifying trends in shapes and materials to reduce their impact. By using a genetic algorithm to optimize the environmental impact of each beam typology (rectangular reinforced concrete, I-beams, or optimized, prestressed, steel and timber beams), and comparing them with one another, it was possible to select the most appropriate for a given scenario (use in a building, a bridge, most favorable and most unfavorable life-cycle analysis scenarios). The study emphasized the fact that beams with a small width perform better environmentally and that the optimized reinforced concrete beams have great potential in reducing the environmental impact, especially for short spans.