KOMINORU Design Splits a Roof Open to Cool a Hyogo House from the Inside Out

The problem was straightforward and familiar to anyone who has lived in a Japanese residential neighborhood: the afternoon sun, unobstructed by adjacent structures along the front of the site, turned the owners' previous home into an oven. KOMINORU Design, led by architect Minoru Ko, responded not by adding mass or shade screens but by cracking the roof itself open. The resulting house in Hyogo Prefecture takes a conventional gable profile and introduces a linear clerestory slit along the ridge, turning the roof structure into both a ventilation engine and a source of controlled, high-angle light.

At 140 square meters, this is not a large house, but it reads as generous. The slit in the roof pulls daylight deep into the interior while the exposed timber frame creates a visual rhythm that stretches every room upward. A planted gravel courtyard acts as a thermal buffer and a borrowed landscape. The whole composition sits quietly within a dense residential fabric, its corrugated metal roof barely rising above its neighbors, yet inside it operates on entirely different terms.

A Gable That Earns Its Keep

From the street, the house presents a clear gable end with its timber rafters fully exposed behind a wall of glazing. It is a legible, almost didactic facade: you see the structure, you see the garden, you see the light filtering through. The planted forecourt with young trees and gravel softens the boundary between public sidewalk and private ground without resorting to walls or fences.

At dusk the logic inverts. The illuminated interior turns the facade into a lantern, each rafter casting shadows across the glazing. The evening view reveals what the daytime view only hints at: the depth of the section and the way the mezzanine level hovers within the gable volume. It is a house that looks best when it is working hardest, glowing from within on a humid Hyogo evening.

Neighborhood Camouflage, Interior Drama

Seen from above, the corrugated metal roof reads as just another pitched volume in a sea of similar profiles. The dark courtyard wall and the compressed footprint keep the house from asserting itself against its neighbors. Mountains rise in the distance, a reminder that Hyogo's geography offers long views even when the immediate context is tightly packed.

The restraint is deliberate. By matching the neighborhood's scale and materiality on the exterior, KOMINORU Design concentrated all the architectural ambition on the section. The slit is invisible from the street and barely legible from the air, yet it governs every interior experience.

Timber Frame as Spatial Armature

Inside, the exposed timber frame does triple duty. Structurally, it carries the split gable roof. Spatially, it organizes the double-height living area into bays that give each zone, kitchen, dining, sitting, a sense of enclosure without partition walls. Visually, it creates a warm, rhythmic ceiling plane that draws the eye toward the courtyard garden and the light beyond.

The courtyard itself is simple: gravel, a few young trees, a low wall. But framed through the floor-to-ceiling glazing it becomes the house's most important room, a middle ground between the controlled interior climate and the harsh afternoon sun outside. The trees will mature, and the courtyard's character will shift with them, a slow clock built into the architecture.

Living Under the Slit

The main living level is a single open volume with grey plaster walls and a kitchen galley tucked beneath the rafters. White and timber cabinetry keeps the palette restrained, letting the structure and the light do the work. A narrow clerestory window slot above the kitchen counter brings a band of sky into the deepest part of the plan, precisely where a conventional roof would trap the most heat.

This is the slit doing its quiet job. Hot air rises to the ridge and escapes; cooler, garden-level air is drawn in through the courtyard-facing openings. The stack effect is basic physics, but it requires a section designed around it. Here the architecture and the environmental strategy are the same thing.

Ascending into Light

A folded metal staircase leads up to the mezzanine and second-floor rooms, where the roof's geometry tightens and the clerestory windows become the primary light source. The staircase itself is minimal, a bent steel plate that keeps sightlines open and avoids competing with the timber frame.

Upstairs, the rooms are smaller and more contained. Floating white shelves line one wall beneath clerestory openings, and a skylight in the bedroom casts angular shadows across the timber ceiling. These upper rooms sit closest to the slit, and they benefit most from its ventilation. Sliding closet doors and flush surfaces keep the detailing tight, letting the angled light and exposed structure define the character.

Thresholds and Compression

The entry hall sets the tone immediately: a vaulted ceiling of exposed wood rafters, a timber door, and a built-in cabinet that absorbs the clutter of arrival. It is a compressed space, deliberately lower and narrower than the living room beyond, so that the release into the double-height volume feels earned.

Flush grey sliding doors elsewhere in the house perform a similar trick, concealing corridors and service spaces behind planes that read as walls until they move. The detailing is precise without being precious. Every transition is calibrated to reinforce the section's primary move: compression at the edges, expansion at the center, light from above.

Plans and Drawings

The plan and section drawings confirm what the photographs suggest: the house is organized around a central courtyard with the living spaces wrapping one side and the service rooms along the other. The section is the real story. The pitched roof splits at the ridge to form the clerestory, and the mezzanine is set back far enough to preserve the double-height volume over the main living area. Numbered rooms suggest a compact program distributed across two floors, with the staircase acting as the hinge between the public ground floor and the private upper level.

Why This Project Matters

Thermal comfort in Japanese houses is an old problem with a long history of elegant solutions: engawa porches, deep eaves, shoji screens that catch cross breezes. House with a Slit Roof belongs to that lineage. It does not rely on mechanical systems or high-tech facades. It splits a roof, plants a courtyard, and lets physics do the rest. The gesture is small, but the effect pervades every room.

What makes the project worth paying attention to is the refusal to treat climate strategy and architectural expression as separate conversations. The slit is not a piece of environmental engineering bolted onto a conventional house. It is the house. Minoru Ko and KOMINORU Design demonstrate that the most effective passive strategies are the ones that shape the section from the start, not the ones added at the end of the design process. In a neighborhood full of overheated gable roofs, that distinction matters.

House with a Slit Roof by KOMINORU Design (lead architect: Minoru Ko), Hyogo, Japan. 140 m², completed 2026. Photography by Katsumasa Tanaka.

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