Around the globe, cities seek to strengthen urban sustainability through increased construction regulations. Existing property rights normally exempt existing buildings from such regulatory changes, a process known as grandfathering. Existing buildings make up the majority of buildings in a city (about 99 per cent), and are replaced very slowly (about one per cent per year). Grandfathering in effect allows for a major weak link in achieving truly sustainable cities. Cities are now experimenting with new forms of governance aiming to solve this problem. Collaboration between city governments, citizens and businesses is key in this new governance.