soeda and associates slices sharp geometry into sonata2 residence

sonata2: a celebration of irregularity

Wedge-shaped sites don’t usually inspire envy among architects, but for Soeda and Associates, the constraints of a sliver-thin plot in Japan‘s Kawasaki City inspire a playfully precise solution. The team’s latest residential project, Sonata2, turns an irregular, triangular lot, pinched between a standard road and a culvert, into a sharp-edged composition that cuts clean through conventional typologies. With no space to waste, every plane is pushed to its limit, every opening calculated for rhythm and relief.

The architecture responds directly to the site’s tight, angular geometry. The building occupies a footprint formed by two intersecting roads — only one of which qualifies as a legal street under Japan’s Building Standards Act. That technicality dictated setbacks on one side only, allowing the architects to stretch the form as close as possible to the boundary on the other. The result is a volume that looks sliced on the bias, a gesture that gives it a surprisingly sculptural street presence.

images © Takumi Ota

soeda and associates rethinks stacked housing

Rather than emphasize the structure’s four-unit layout, Soeda and Associates visually unifies Sonata2’s mass by tapering the form and playing with fenestration. Large, varied openings cut into the walls with intentional asymmetry, dissolving the usual cues of residential repetition. The strategy disguises the building’s function while animating its facades, a formal solution that’s as design-minded as it is about obfuscation.

With the site too compact for an elevator, the architects embrace verticality the old-fashioned way, with a flight of exterior stairs. The highest unit is accessed at the fourth floor, with the apartment split into a fourth–fifth floor duplex. The stairs thus become an architectural narrative device, connecting not just levels but experiences. Diagonal cuts in both plan and section introduce unusual sightlines and interior voids, creating an illusion of expanded space inside a decidedly compact volume.

Sonata2 is designed for a triangular site in Kanagawa, Japan

sharp angles stabilized with concrete precision

Soeda and Associates’ Sonata2 residence is structured in reinforced concrete with walls carefully placed to handle seismic loads. Though the floor plan’s acute angles might suggest structural imbalance, the architects used both material heft and spatial strategy to distribute weight. The external staircase contributes to this equilibrium, aligning the building’s center of gravity with its center of rigidity. It’s a thoughtful strategy that keeps the building stable while maximizing usable interior space.

A standout structural element of the house is its top-floor roof, supported at a single point like a precariously balanced toy. T-shaped steel beams embedded in the slab mitigate this drama, offering stability without undermining the delicate aesthetic. Meanwhile, a 100 millimeter- (3.9 inch)-square concrete column supports the external stairs, puncturing through the landings with minimalist confidence.

While the project may read as compact in plan, it proves that welcoming interiors don’t rely on scale. With dynamic diagonals, shifting volumes, and rigorously engineered minimalism, the building turns constraint into concept. Every corner holds a moment of surprise, and every inch has been earned by strategy.

the four-unit layout is disguised with bold punched windows