COZEB3: study and optimum cost analysis tool, determination of the optimum level of performance as a function of costs, sensitivity analysis of results and development of an IT tool. The objective of this COZEB study is therefore to verify that the current (or already projected) energy performance requirements set in the Walloon Region are not more than 15% lower than the result of the cost-optimality calculation. Based on the previous Cozeb and Cozeb suite studies, an IT tool is being developed as part of the COZEB3 project. This tool is a computer system for the automatic implementation and analysis of data relating to ILL. The goal is to determine cost-optimum requirement levels and perform economic sensitivity analyses for a series of parameters.