U.GA Architects Wraps a 51 m² Glass Wedge Around a Red Spiral Stair at a Busan Alley Junction

Haeridan-gil in Busan is a neighbourhood of former residential streets, old Western-style houses and narrow alleys that have been reworked into a cultural streetscape. Into one of its sharpest corners, where a 4-metre lane meets a 15-metre road at an acute angle, U.GA Architects has inserted Koma, a commercial building of just 51 m². Lead architect Dae-woo Yu, with Soon-jung Shim and Hyo-kyung Kwon, has built a two-storey glass box with a red roof edge, a mesh parapet and a cylindrical stair top that pokes above the roofline.

What interests us here is how much civic presence a building this small can claim without shouting. The architects frame the value of the project as a matter of attitude and attunement to its setting rather than size. In practice, that means a triangular plot is treated as an asset rather than a problem, a spiral stair becomes the organising element of the whole building, and the roof works as a public face as much as the street elevation does.

A Wedge Where the Alleys Converge

Acute corner sites usually produce awkward buildings: leftover triangles, blind points, wasted floor area. U.GA does the opposite and follows the wedge exactly, so the building reads as a clean extrusion of the plot. Seen from the sloping street, against dense hillside housing, it holds the junction like a marker post.

The fully glazed walls do two jobs. By day they reflect the neighbouring towers and stone-clad buildings, so the box partly dissolves into its surroundings. They also put the interior on display to anyone walking past, which is exactly what a ground-floor food business needs on a pedestrian street.

The Roof as a Fifth Facade

Busan is a city of slopes, and a low building here is seen from above as often as from the side. U.GA clearly understood this. The triangular red roof, punctured by a round stair cap, reads as a graphic figure among parked cars, lilac trees and neighbouring rooftops. From the hillside, the building is a red triangle with a dot in it, a logo made of architecture.

The red fascia also gives the glass box a crisp edge. Without it, a two-storey glazed volume this small could look provisional. With it, the building has a cornice line that frames blossom branches and sky in a way any passerby can photograph.

Terrace, Mesh and Cylinder

The roof is usable. A red mesh guardrail wraps the terrace, and the cylindrical stair enclosure rises at one corner as both arrival point and landmark. The mesh is the smart choice here: it meets the safety requirement while staying visually light, so the parapet adds colour without adding bulk to a building that depends on looking slim.

At dusk, the curved stair cap and the red railing sit against a pink and grey sky, and the composition becomes almost toy-like. We mean that as a compliment. On a street remade for cultural visitors, a building that is legible and a little playful is doing its job.

A Spiral Stair Carrying the Whole Plan

In 51 m² spread over two floors and a roof, a conventional straight-run stair would eat a ruinous share of the floor area. The spiral solves the circulation problem in a compact footprint, and U.GA makes it the centrepiece. It is painted red and wrapped in a curved perforated metal shell, and it runs through the building like a vertical spine, visible from the street through the glass.

Inside, the materials stay honest: exposed steel beams, a concrete floor, afternoon sun falling across both. Looking down through the mesh shell, lit by a glowing edge strip, the stair turns movement into an event. For a small restaurant, that gives customers a reason to climb to the upper floor and on to the terrace.

A Lantern After Dark

Glass buildings earn their keep at night. Once the interior lights come on, Koma turns into a lantern at the junction, with the red spiral stair showing clearly through the front elevation. Against a deep blue evening sky, among utility poles and wires, the lit cylinder on the roof becomes a beacon for the street.

This matters for a cultural streetscape that has to work after office hours. A small building that glows contributes to the evening life of the whole street, not just to its own business.

Signage at Shopfront Scale

Branding is handled with restraint. A teal panel and a vertical KOMA sign sit inside the glass grid, and the backlit lettering on a translucent panel sits above a concrete block base. The sign is built into the facade system rather than bolted onto it, which keeps the elevation coherent.

The concrete block base deserves a note too. It anchors the glazing to the ground with a heavier, more ordinary material, and that makes a quiet link to the masonry of the older neighbourhood.

Plans and Drawings

The site plan states the premise plainly: a triangular flat roof and a circular stair tower squeezed between a 4M road and a 15M road. The ground and second floor plans show an elongated triangular footprint with the spiral stair set inside and restaurant space filling the remainder. The roof plan places the circular enclosure near the apex of the terrace, so the stair arrives at the narrow point and leaves the wider end free for occupation.

The sections are the most revealing drawings. Figures climb the stair core from ground level to the screened roof terrace, and the vertical route is drawn as the main experience of the building. The elevations confirm the facade logic: a seven-bay grid at the front, folding doors at ground level on the side to open the interior to the street, and a screened rooftop volume that caps every view.

Why This Project Matters

Most commercial buildings in revitalised neighbourhoods either mimic the old fabric or ignore it. Koma does neither. It accepts a difficult acute-angled plot, uses a limited palette of glass, steel, aluminium and mesh, and gets its identity from one strong spatial move: a red spiral stair that ties street, floors and roof together. The result is a building that is easy to read, easy to remember and useful to the street around it.

For architects working on tight urban infill, the lesson is clear. Small does not have to mean timid. When the roof is treated as a facade, circulation as an attraction and the site's awkwardness as its character, 51 m² can hold a corner with as much confidence as a building many times its size.

Koma Commercial Facility by U.GA Architects (lead architect Dae-woo Yu; design team Soon-jung Shim and Hyo-kyung Kwon), Haeridan-gil, Busan, South Korea. Area: 51 m². Completed 2025. Photography by Sangin Nam.

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