Shaped like a cluster of barnacles, the House in Kohoku doesn’t exactly blend in with its neighbors. Located in a hilly suburb of Yokohama, it has neither the conventional pitched roof nor the standard-issue wood frame. But contained within its reinforced concrete shell is a barrier-free home for a nautical architect and his wife who were ready to chart a new course.

Their children grown and gone, the couple no longer needed the two-story home they built 35 years ago on their flag-shaped property hemmed in by buildings. (“My parents inherited this land from my grandfather and built the old house,” explains the clients’ adult son. “But they wanted a new house to accommodate their lifestyle change.”) Not to mention, their old house had a number of shortcomings – it was cold, dark, and lacked adequate display space for the hundreds of dolls the wife collected while traveling the globe with her husband. So the clients decided to “scrap and build” and asked Torafu Architects to take the helm.

Nodding politely to the old house, the architects kept and reinstalled the original front door, an ornately carved wood panel that contrasts with the smooth concrete. It leads into the entry foyer, an auxiliary vestibule attached to the one room dwelling. Divided into quadrants, the home’s simple, square plan consists of four, distinct areas: kitchen, living room, bedroom, and bathroom topped by a loft that serves as a home office. Accessed by a ladder-like stair, the work area is as compact as a ship’s galley. “It expands the interior but it is an incredibly small space,” says the clients’ son, who ought to know since the loft is his graphic design office. An additional appendage at the rear holds storage and a walk-in closet.

The trick was how to distinguish the functional parts yet maintain the integrity of the whole. “Connected but separate, that’s the theme of this house,” explains Torafu principal Koichi Suzuno. Undifferentiated by full height partitions or the sliding screens commonly used in Japan, the floor plane unifies the house. But at the ceiling level, individual tubular roofs cap the quadrants and branch off in different directions. Topped with a skylight, each roof lets in a modicum of daylight, animating the interior with an ever-changing dance of shadow and sunshine while forging a direct link between interior and exterior.

Because of Kohoku’s densely-populated, terraced topography, this was no mean feat. Since the neighboring house to the north sits on higher ground, accessing the coveted southern exposure was a problem. Blocking sight lines from above necessitated the careful study of both skylight angles and roof shapes. At the same time, external considerations had to mesh with internal height requirements: while the kitchen’s roof had to be low enough to bounce reflected light onto the counters, the bathroom’s roof soars to 23-feet to accommodate the loft. “The volumes on top are definitely not residential in scale,” comments Suzuno.

Yet all four roofs converge at a single spot in the middle. Inside the house this center point is equally important. From here concrete wedges corresponding to the valleys between the roofs descend towards the perimeter walls. While their solid mass separates the quadrants, the slanted openings beneath preserve room-to-room continuity. Furniture placement and custom upholstery fabric underscore the divisions, but uniform interior finishes and the ubiquitous doll collection – thanks to built-in cabinetry they are visible throughout the house – pull it all together.