FujiwaraMuro Architects Suspend a Glass Sunroom Inside a Split-Level Concrete House in Tsukaguchi

A house built on the footprint of a family's former home carries emotional weight that most briefs never mention. In Tsukaguchi, a quiet residential pocket in Hyōgo Prefecture, FujiwaraMuro Architects replaced that older dwelling with something that turns a single programmatic wish, a sunroom, into the governing idea for the entire building. The result is a 105-square-meter residence split into two concrete volumes with a suspended glass box hovering between them, collecting and redistributing light the way a prism refracts a beam.

What makes the project genuinely interesting is that the sunroom is not a room in the conventional sense. It is an infrastructure of light. Positioned beneath a top light and lined with glass on all sides, including the floor, it turns plants into overhead ornaments visible from the kitchen below, bounces reflected daylight onto walls and ceilings across split levels, and at night glows from within like a paper lantern scaled up to architecture. The move simultaneously reduces building volume, cuts cost, and gives the house a spatial generosity that its modest footprint would never otherwise allow.

Two Volumes, One Slit of Sky

From the street, the house reads as two grey concrete boxes pushed close together with a narrow glazed recess between them. At dusk the entrance slot glows yellow, signaling the warm interior beyond without revealing much of it. The split between volumes is more than aesthetic: one mass houses the LDK zone, the other contains private rooms. A narrow exterior passage between the two walls opens to blue sky overhead, letting air and light penetrate before you even step inside.

The facade is deliberately mute. Concrete surfaces carry no ornament, and window openings are few and small. This restraint is strategic. It forces all the spatial drama inward and upward, toward the sunroom and the skylights that crown it. In a dense residential context, the move also grants privacy without requiring curtains or screens, a pragmatic courtesy to neighbors that doubles as an architectural discipline.

The Floating Glass Core

Look up from the concrete kitchen island and you see greenery framed in steel and glass, suspended overhead on a bridge that doubles as the sunroom floor. The glass is structural enough to walk on and transparent enough to let you watch someone tending plants from two levels below. It collapses the vertical distance between daily routines: cooking and gardening happen within eyeshot of each other, separated only by a plane of light.

The cantilevered bridge and its steel supports are left exposed, painted black, and allowed to read as industrial elements against white walls and raw concrete. There is no attempt to conceal the mechanism that holds the sunroom aloft. The honesty is refreshing. Structure becomes decoration, and the house wears its engineering as openly as its planting.

Split Levels and Vertical Connections

The interior is organized across split levels that stagger the LDK zone so that no two adjacent spaces sit at the same height. The living area opens to the glass courtyard on one side and a steel staircase on the other, with skylights pulling diffused daylight down through the section. Standing in the kitchen, you can see through the glass floor above, across to the stair, and up to the roof light. The sightlines are long relative to the plan's compactness.

Split-level planning is common in Japanese residential work, where land is expensive and lot sizes are tight. FujiwaraMuro Architects use it here not just to gain usable area but to construct a continuous visual field. Family members on different floors remain connected by overlapping views and shared light, a condition that makes 105 square meters feel considerably more generous than the number suggests.

Steel, Glass, and the Weight of Light

The staircase is a piece of furniture as much as it is circulation. Black steel stringers and handrails thread between glass partitions, framing views at each landing. Afternoon sunlight slices through the skylight grid above, casting sharp geometric shadows on white walls and the concrete countertop below. These shadow patterns migrate throughout the day, marking time the way a sundial does, slowly and without sound.

Material choices lean deliberately raw. Concrete is board-formed and left unfinished. Steel is painted but not clad. Glass is clear, never frosted. The palette is austere, yet the surfaces reward attention: light plays differently across porous concrete than across smooth steel, and the contrasts accumulate into a tactile richness that compensates for the limited material vocabulary. FujiwaraMuro Architects rely on a long Japanese tradition that finds beauty in aging materials, expecting the steel and concrete to patinate and soften over the years.

Interior Retreats and the Reading Nook

Not every corner of the house shouts. Tucked beside the glass-enclosed courtyard, a small reading nook offers a seat among potted plants with the staircase visible through a glass partition. It is the kind of space that rewards stillness: sit long enough and you notice the light shifting, leaves swaying, and the shadow of the steel frame sliding across the floor. At night the same alcove, seen from outside through steel-framed glazing, becomes a warm tableau of domestic life, the potted plant and kitchen counter visible behind the glass like objects in a vitrine.

The night view is worth pausing on. The suspended sunroom glows from within, its illuminated glass volume transforming the house's character entirely. What during the day is a light-catching device becomes after dark a light-emitting one. The inversion is elegant and it is the clearest proof that the sunroom is not an add-on but the conceptual engine of the whole project.

Plans and Drawings

The floor plans reveal an angled geometry that is not immediately legible from the photographs. Walls splay to widen sightlines and channel movement around the central courtyard and stairwell. The first floor tucks the entrance, bedroom, and kitchen into a compact footprint; the second floor opens outward with the living space and sunroom occupying the most generous volumes. Roof plan hatching indicates timber decking around the central skylight, suggesting an outdoor terrace that mediates between the two concrete masses.

The sections are the most revealing drawings. They show how the split levels cascade from the entrance down to the dining kitchen and further to parking below grade, threading vertical circulation through the center of the house. The sunroom reads clearly as a mid-height insertion, its glass floor aligning with neither the level above nor the level below. Numbered rooms on the section confirm that every usable space in the house has a direct or reflected relationship to the central light shaft. Nothing is left in shadow by default.

Elevations confirm the street-facing reticence. The north, east, south, and west facades each present a nearly blank concrete plane, punctuated only by narrow vertical slots or small square windows. The rooftop element visible on the north elevation and the slatted screens on the south suggest controlled ventilation and solar management, though the primary climate strategy remains the passive diffusion of light through the sunroom and skylight system.

Why This Project Matters

In a country where residential architecture frequently defaults to either white-box minimalism or exuberant formal gestures, the Sunroom House takes a third path. It starts from a single programmatic request, builds a structural and environmental strategy around it, and lets that strategy shape every dimension of the plan. The suspended glass volume is not a gimmick. It solves real problems: it reduces enclosed volume to cut costs, it channels natural light into a compact interior, and it creates the visual connections that allow a small family house to feel open without wasting space.

FujiwaraMuro Architects demonstrate that innovation in residential work does not require exotic materials or inflated budgets. Steel, concrete, and glass are ordinary. What is not ordinary is the precision with which they are combined here: a glass floor you can stand on that also serves as a garden display, a skylight that doubles as a sunroom roof, exposed structure that doubles as interior composition. Every element pulls double duty. That economy of means, stretched to its limits and then lit from above, is the real lesson of this house.

Sunroom House, Tsukaguchi, Hyōgo, Japan. Architect: FujiwaraMuro Architects. Area: 105 m². Year: 2024.

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