You won’t find any insulation in the walls of architects Yoshichika Takagi + Associates’s House in Japan. Instead, the two-story house keeps warm by taking its cue from greenhouses–large polycarbonate panels bring in sunlight and heat up the space. The architects set up the house so that a sunroom at the core takes in the most sunlight, warming the rest of the house from the center outward. A lovely exposed timber frame opens the place up (we covered a similar design here), and makes the interior of the house match the exterior. Though no insulation makes way for a stripped-down, minimalist feel, we can imagine that it also gets pretty noisy with just wooden walls separating the rooms. Another potential problem? The temperature of the sunroom–anyone who has spent time in a greenhouse in the summer knows how quickly sun-soaked spaces can turn into saunas.