Just a little post about a 1970s house in Niseko I was lucky to stay at. It's common to have double-glazed windows in Hokkaido unlike the rest of Japan, so one would expect a higher level of insulation, but well, the walls are still made of wood and cardboard so it doesn't really help, it's extremely cold. No matter how many square meters you have at your disposal, the functional space will always shrink into a small life-saving volume around your gas heater or a burning stove. In Japan the concept of getting warm is revolving not around the house, but the body itself. Instead of wasting energy on central heating, people take baths, sit around kotatsu, near the stove, air-conditioner or even use chemical hand warmers. European-style heating systems are not welcomed for several environmental reasons (earthquakes are one of them), but maybe there's a cultural concern, too: when it's warm in just one tiny area, you get closer together with the others and it's just cosier that way?
