Four Decks is a 114.75 square metre residence in Sapporo, Hokkaido, organized around four split-level floor plates that extend a sloping corner site into the domestic interior. Designed by Yosuke Tomiya Architectural Design, the house uses a central void, calibrated openings, and a compact insulated envelope to connect family life with changing views of mountains, parkland, and the city.
Four Decks Technical Information
- Architects: Yosuke Tomiya Architectural Design
- Location: Sapporo, Hokkaido, Japan
- Gross Area: 114.75 m2 | 1,235 Sq. Ft.
- Project Years: 2018 – 2018
- Photographs: © Koji Sakai
The house extends the slope of the site into four connected floor levels, creating a continuous interior in which changing heights produce changing relationships between people, light, and landscape.
– Yosuke Tomiya
Topography as Spatial Framework
Four Decks occupies a corner plot at the foot of the mountains in Sapporo, where the ground rises by approximately two meters across the site. Rather than cutting the terrain into a level building platform, the project adopts the gradient as its primary ordering device. The result is not a house placed upon a slope, but one whose internal section continues the movement of the land.
Four floor plates, identified as Deck 1 through Deck 4, rise from ground level in increments of 1,160 millimeters, 2,750 millimeters, and 3,620 millimeters. Their staggered arrangement sits beneath a single flat roof, creating a sectional alternative to the conventional two-story house. Ceiling heights shift with program, from more compressed private rooms to the taller living and dining areas, so circulation becomes an experience of altered eye levels, outlooks, and degrees of enclosure.
This sectional organization also gives the modest footprint a greater spatial range. The lower earthen-floor hall opens toward the garden, while the principal living spaces occupy elevated decks with broader views. The sequence avoids a simple opposition between ground floor and upper floor. Instead, the house is organized as a graduated terrain of domestic situations, each defined by its relationship to the ground, the roof, and the surrounding horizon.
The Central Void and Domestic Connectivity
A central void binds the staggered levels into a single visual and acoustic field. From the entrance hall, occupants can register stairs rising through the house, glimpses through internal openings, and the presence of rooms above and below. This continuity counters the potential fragmentation of split-level planning, allowing the residence to be understood as one connected volume despite its changing floor heights.
Open timber treads, slender timber handrails, and black steel mesh maintain permeability at the void’s edges. The mesh functions as both balustrade and horizontal play surface, allowing light and sightlines to pass through elements that would ordinarily become opaque safety barriers. Its use introduces a deliberately infrastructural texture into the timber interior, making the vertical circulation zone legible as a working framework rather than a sealed architectural spectacle.
The arrangement proposes privacy as a matter of gradation rather than total separation. Bedrooms and service spaces retain enclosure, yet family members can remain aware of movement and activity elsewhere in the house. A person at the dining table, a child using the raised platform, and someone arriving through the hall occupy distinct levels while remaining perceptually connected. This compact domestic model uses visibility to support shared occupation without eliminating retreat.
Openings, Landscape, and Exterior Legibility
The facade records the logic of the section. Rather than aligning windows in the horizontal rows associated with conventional storeys, openings appear at varied heights corresponding to the four decks. Square punched windows, larger framed views, and vertical apertures disclose the staggered organization within, giving the elevations a measured irregularity grounded in interior use rather than graphic composition alone.
Each opening addresses a specific condition around the corner site. Windows frame distant mountain slopes, the vegetation of a neighboring park, nearby roofs and utility lines, and the city below. A diagonal opening brings southern daylight into the interior while directing attention toward the mountain landscape. These views are not treated as a single panoramic image; they are distributed across the sequence of levels, making orientation inseparable from movement through the house.
The exterior envelope is clad in dark pre-painted galvanized steel with vertical standing seams that give the compact mass a finely ribbed surface. White projecting volumes mark the entrance porch and balcony, interrupting the dark field with sharply defined elements. Their contrasting color and geometry identify points of arrival and outward extension, while the varied openings make the internal split levels readable from the street. A concrete retaining plinth follows the changing ground level and mediates between the building, gravel edges, planting, and road.
Adaptability, Materiality, and Cold-Climate Living
Several areas in Four Decks resist fixed program. The multipurpose deck can serve as a play area, work zone, drying space, storage platform, or occasional guest area as household needs change. This flexibility is achieved less through movable partitions than through intermediate spaces with sufficient access, daylight, and visual connection to support changing forms of occupation. The under-stair study similarly converts residual volume into an inhabited workplace and bookshelf.
Material transitions clarify use while preserving continuity across the interior. Oil-finished birch flooring runs through the principal living spaces and is echoed in the stairs, joinery, exposed beams, and dense rhythm of ceiling joists. The timber structure remains visible above the living and dining room, giving the larger upper volume a tectonic order. At the entrance, smooth grey mortar flooring distinguishes the more utilitarian genkan zone from the warmer domestic areas without requiring a full spatial separation. Stainless steel work surfaces and glass kitchen screens introduce durable, reflective materials into this predominantly timber setting.
The house responds to Sapporo’s severe winter conditions through a layered thermal envelope: 105 millimeters of high-performance glass wool insulation is supplemented by 50 millimeters of exterior XPS insulation, while triple-glazed resin-framed Low-E windows reduce heat loss at the openings. PVC roof waterproofing protects the shallow roof profile, and the compact external volume limits exposed surface area. These measures allow the project to sustain large areas of glazing and long internal sightlines while addressing the climatic demands of northern Japan.
About Yosuke Tomiya Architectural Design
Yosuke Tomiya Architectural Design is based in Sapporo, Hokkaido, Japan, and is led by architect Yosuke Tomiya. The practice designs private houses and small-scale architecture that respond to Hokkaido’s climate and topography.
Credits and Additional Notes
- Client: Young family
- Construction company: Assist Kikaku Co., Ltd.
- MEP consultants: Electrical Works: Shinwa Co., Ltd.; Mechanical and Plumbing: Sapporo Nippuro Co., Ltd. and Ono Setsubi Co., Ltd.
- Other contributors: Custom Kitchen, Furniture, and Joinery: Shoryu Mokkosha Co., Ltd.; Timber Entrance Door: m.a.p; Photography: Koji Sakai / Graytone Photography
