Engineering design processes are often technology-centred and have difficulties adequately integrating user behaviour in product design. Although, industry and academia agree that the human aspect is important for the success of a product, there are few methods and tools that help designers with such factors during the synthesis of the design process. This paper covers multi-trade engineering design, and deals with the development of a behavioural design approach to help designers optimize product performance in the design phase by taking into account use conditions and requirements. This method integrates user and product behavioural data as design work. These two behavioural are defined as tasks to do by user and product. So a set of solutions could be considered before choosing a final solution. Thus, a software application is being developed to support and allow a systematic utilization of the "behavioural design approach" (BDA) by integrating it into the daily work of the designer. An application is presented to show the applicability of our method. Relevance to industry The article describes a behaviour design approach to be used by industrial engineers, designers and ergonomists for ergonomic analysis and evaluation in product or machine design. The approach has been developed for both expert and non-expert practitioners, who can integrate user behaviour and product behaviour during the design phase for improving product performance