When 33-year-old Japanese architect Miwa Mori was a student in Germany, she learned a lot about architecture by observing fashion. “In winter in Germany, people wear t-shirts inside and put on a heavy jacket to go out. In Japan, we bundle up inside and put on a light coat to go out,” she notes. That’s because German houses are some of the most energy-efficient in the world, while the minimalist wonders we swoon over in Japan usually have poorly-designed skins that let in cold air during winter and hot, humid air during summer. Now Mori is back home and on a mission to build more comfortable homes. At Key Architects, the firm she runs with husband Joerg Heil, she’s blending the super-energy-efficient design skills she learned at Germany’s Passivhaus (or Passive House) Institute with traditional Japanese building methods—and reducing the carbon footprint of the country’s energy-sucking residential sector while she’s at it.