In order to lower the huge carbon dioxide emissions due to building heating, the goal of this communication is to show how the design of insulation panel layout can be strongly computer-aided during façade building energy renovation projects. The work has been achieved during an applied collaborative research project (ISOBIM), whose purpose is to develop open web integrated decision-aided tools to support a whole digital engineering retrofitting processes using modular timber framing panels. First, the panel layout design problem is analyzed and permit to identify a four steps design process supported by three data models. Then, once the problem is preprocessed to remove some singularities, an automatic layout design algorithm is proposed and discussed. An example illustrates the propositions and support discussions