We are seeing examples of more extreme weather conditions than ever before. The most threatening one for our most vulnerable citizens, the very young and the elderly, is heat. As the density of our cities increases and the elderly population continues to grow, we are challenged to design urban environments that will be resilient to extreme heat and prolonged heatwaves. We will have to apply the design principles of building social and physical structures for both a 2-year-old and an 80-year-old person, to provide safe, liveable and enjoyable environments.