In previous works [14], models and processes enabling to make interacting a project planning process with the system design one have been presented. Based on the idea that planning and design processes can be guided by consulting past experiences, an integrated case-based approach for coupled planning project and system design processes is proposed in this article. The proposal is firstly based on an ontology of concepts that permits to gather and capitalize knowledge about objects to design, i.e. tasks and systems. Secondly, the integrated case-based process is presented taking into account planning of tasks and tasks of design. For the retrieve task, a compatibility measure between requirements and past cases is calculated. It is based on the semantic similarity between past and required concepts as well as past solutions and new requirements. Finally, integrated adaptation and retention of new solution(s) are done.