Shimpei Oda and Loowe Inc. Hollow Out an Osaka House to Let Concrete Floors Do All the Work

When Shimpei Oda Architect's Office and Loowe Inc. first stepped into this three-story steel frame in Osaka's Kohama district, the interior had already been stripped bare. The previous layout, a warren of small rooms evidenced only by mismatched window openings left behind on every wall, was gone. What remained was a raw skeleton of steel columns, beams, and deck plates with a distinctive reddish Etruscan finish. Rather than fill that skeleton back up with conventional partitions, the architects asked a different question: what if the floor itself could organize the house?

The answer is a renovation completed in 2022 that treats concrete floor planes as three-dimensional objects. Shifted, split, and punctured, these floors create gentle separations between living zones without ever resorting to full-height walls. The result is a 104 m² home designed for residents who own few possessions and prefer their favorite furniture to speak louder than their architecture. It is a quiet project, but the thinking behind it is anything but simple.

Raw Frame, Reddish Bones

From the street, House in Kohama reads as an unremarkable white stucco volume with a gabled entry and corrugated metal screens. Nothing signals what happens inside. Step through the door, though, and the original steel structure announces itself immediately. Columns, beams, and ceiling plates retain their reddish-brown finish, a warm, almost terracotta tone that sets the entire interior palette. Against pale plywood walls and polished concrete underfoot, these exposed members create a rhythm that is industrial without being cold.

The decision to leave the steel raw was both pragmatic and atmospheric. Refinishing would have added cost to a project that already embraced economy as a virtue. More importantly, the aged patina gives the house a sense of time that no new material could replicate. The structure becomes decoration, and decoration becomes unnecessary.

Concrete as Spatial Device

The conceptual heart of the project is the treatment of concrete floor slabs as something more than horizontal surfaces. By varying their levels and introducing openings, the architects turn the floors into a three-dimensional system that simultaneously organizes circulation, admits light, and defines zones. A concrete stair landing on one level becomes the boundary between kitchen and corridor. A floor opening ringed by a steel handrail on another level creates a visual connection between stories while letting daylight filter downward.

These moves replace what walls would ordinarily do. Storage room, kitchen, carpeted area, bedroom: each occupies its own position within a multi-leveled landscape. You sense the separations underfoot before you register them visually. It is a remarkably effective strategy for a narrow urban house, where erecting full partitions would choke both light and airflow.

Vertical Stitching

A steel staircase threads through all three floors, its diagonal line cutting across the exposed timber joists above. On the second and third floors, it connects to balconies that look back down onto the ground-level concrete plane. The stair is deliberately legible: thin steel stringers and open treads that let you see through to the rooms beyond. It occupies minimal visual mass while doing maximum spatial work.

Track lighting runs along the ceiling structure to supplement what the scattered windows provide. Those windows, inherited from the previous layout and left in their original positions, bring light from different directions on every floor. Rather than regularize them, the architects accepted the randomness. The result is an interior where light shifts unpredictably through the day, giving each zone a slightly different character depending on the hour.

Living Lightly on Three Floors

The clients wanted a home suited to a minimal way of life, and the architecture obliges. The kitchen sits beneath the exposed ceiling as a plywood island, functional and unadorned. Upper hallways are lined with pale plywood panels and glass-railed openings that preserve sightlines. A centered square window at the end of one corridor frames a single view with the precision of a painting. There is almost no applied finish in the house. Materials are either structural or utilitarian, and the few pieces of furniture the residents chose fill the space with personality that wallpaper never could.

The double-height volume at the center of the plan is the spatial payoff. Concrete stairs ascend alongside the steel stair, and the eye can travel from ground floor to roof structure in a single glance. For a 104 m² house, this kind of vertical generosity is rare. It makes the home feel significantly larger than its footprint, a gift that comes directly from the decision to carve away floor area rather than add partitions.

Plans and Drawings

The three-level floor plans reveal the project's organizational logic clearly. The ground floor accommodates the garage and entry alongside the main stairwell. Living spaces, kitchen, and bedroom distribute across the upper levels, each floor slightly different in its arrangement of openings and level changes. The axonometric drawings are even more revealing: seen in three dimensions, the staggered concrete planes and the continuous stair read as a single interconnected landscape rather than a stack of isolated floors. Furniture placement is sparse and deliberate, confirming that the architecture itself is the primary spatial element.

Why This Project Matters

Renovation projects rarely get credit for conceptual ambition. Most are exercises in cosmetic repair or pragmatic reconfiguration. House in Kohama operates on a different level. By treating the concrete floor slab as a malleable, three-dimensional element rather than a fixed datum, Shimpei Oda and Loowe Inc. found a way to reorganize an entire house without adding a single conventional wall. The strategy is transferable: any steel or concrete frame with adequate headroom could benefit from this thinking.

The broader lesson is about restraint. When the structure is already beautiful, when the windows already exist, when the clients already know how they want to live, the architect's job is to remove what is unnecessary and sculpt what remains. In Kohama, that sculpting happened in concrete, and the result is a house that feels both inevitable and inventive.

House in Kohama, designed by Shimpei Oda Architect's Office and Loowe Inc., Osaka, Japan. 104 m². Completed 2022. Photography by Norihito Yamauchi.

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