The architects at SPACESPACE were definitely thinking outside of the box when they designed this residence in Osaka. The Ground Roof House is a two-story, three bedroom home that features a crazy bathroom setup. First, the bathroom is located smack dab in the middle of the living room. Second, it's buried slightly underground beneath a concrete bunker-like shell with an army green enclosure on top. The canvas is designed to work with the south-facing windows to collect and store heat as thermal mass - certainly a plus for the wacky house.
The compact home is located in a friendly neighborhood with some long-time residents, so the new owners wanted to make sure they built a home that was open and inviting. Building codes also let them build higher than a traditional two-story building, so they bumped up the downstairs ceiling height to give the lower level a feeling of luxury. Upstairs is more private and includes three bedrooms and open communal hallways, which include two desks for private study and work. Downstairs holds the living, dining, kitchen and bathroom.
The bathroom is an artificial hill made of concrete, slightly submerged into the floor and covered in canvas much like a removable sofa cover. A bench was built into the hill and covered in canvas and cushions to act as a couch. Pockets were sewn in to hold toys, remote controls and other goodies. Then bunker bathroom comes complete with a bathtub and can be accessed by a set of small stairs.
Solar passive design was an integral part of the home’s construction and is used to pull in daylighting and solar heating during the winter. A large south-facing window located up high takes in the sun and aims it directly onto the bathroom bunker, storing heat during the winter; in the summer, the sun is too high to come into the home directly. A double wall on the second floor on both the north and south sides of the home encourages ventilation and lets hot air from downstairs escape. Electric blinds can also be rolled down over the south facing windows in the event it is too hot.