In the Global North, meeting the need for affordable, climate-resilient housing also requires innovation in new construction, but even more crucial is retrofitting. With 80 percent of 2050’s housing stock already standing, decarbonizing it will have a greater impact than low-carbon new builds. What’s more, much of the social housing that was built in the mid-to-late 20th century—now a scarce resource—is starting to fail. Saving and upgrading it can be done for a much lower cost, both in terms of money and embodied carbon, than tearing it down and building new.