For cities, climate change is a major concern due to its severe impacts and its inherent complexity. City and building designers could be pivotal actors, but have yet to fully take on this role. Research can support adaptation action through greater collaboration with practitioners and a better understanding of their knowledge and practices. This paper presents results from a research project undertaken in Toulouse (France) last year. Urban practitioners were consulted through an online survey and observed in action during two design workshops. The findings highlight: (i) the hidden knowledge within design practice; (ii) the importance of providing designers with solution-focused and form-giving data; and (iii) the potential offered by design constraints to trigger changes in the practices of professionals.