As our society experiences a significant demographic expansion, 350 000 new households in Wallonia will need to be erected by 2040. However, the Belgian index of construction costs is constantly increasing due to building lots scarcity and high requirements in terms of energy efficiency. A funding problem appears as the Walloon average income has not improved, hence the need to control building costs in order to offer quality accommodation for everyone. This two year research aims to create a support tool reducing costs of new buildings without jeopardizing comfort, structure or durability. Three action plans are set in order to achieve this goal: the optimization of wall building systems, the development of more efficient habitation practices and the restructuration of the organizational model of building companies. The present paper states the first action plan of the study, namely the optimization of the wall building systems. The final objective of this first step is to highlight the factors impacting significantly on wall prices and to offer more economical or ecological solutions. During this first step, the authors defined the most used building systems for each type of wall. They determined some relevant variants of the reference building system and established their price and environmental performances. At the present time, the research compared only facade wall building systems. As of yet, the results are not extensive enough to draw definitive conclusions. However, preferential choices are presented providing relatively good environmental and economical performances. More general findings have also been highlighted but still require verification; for instance, the larger the amount of different layers that are assembled in a building system, the higher its price will be. Additional analyses are needed to extract aspects that will have a decisive role in the optimization task.