A spacious loft room bordered by a slender handrail is located beneath the steeply sloping wooden rafters of this Tokyo house by Apollo Architects & Associates (+ slideshow).

Featuring an asymmetric pitched roof, the three-storey building provides a home for a family of four on a narrow site in Mitaka – a newly established city on the outskirts of the Japanese capital.

Apollo Architects & Associates – which also recently completed a raw concrete house for a pair of art collectors – was asked to base the design on the work of Finnish architect Alvar Aalto and the small churches of northern Europe, which one of the clients had visited.

Recent examples of this typology include a copper-clad chapel in Finland with a boat-inspired interior and a contemporary reinterpretation of a traditional Norwegian stave church.

This led to an interior dominated by wooden surfaces, particularly the loft that takes up the entire upper storey. It also prompted the house's name, Nord.

"The living spaces are filled with the warmth of wood, which is somehow similar to idyllic scenery in Japan," said architect and studio founder Satoshi Kurosaki.

Conceived as a large playroom for the clients' two daughters, the loft is set back from the walls to create views down to the open-plan living and dining room below.

The centre of the room almost lines up with the peak of the asymmetric roof, ensuring enough head height for occupants.

Related stories: more architecture by Apollo Architects & Associates

The exposed wooden rafters are made from SPF – a kiln-dried lumber consisting of spruce, pine and fir. They also support slender metal handrails, which extend from the staircase.

"The small loft space unfolds as a compact but comfortable kids' room that resembles a tree house," explained Kurosaki. "At night, cove lighting illuminates the rafters and creates a dramatic expression unlike that of daytime."

"The loft is intentionally designed without walls," he added. "Instead, handrails hang from the ceiling in order to create a space with a unique floating feeling."

Windows puncturing the flat walls and a long skylight stretching across the roof ensure plenty of natural light reaches this room as well as the living and dining spaces below. The staircase also allows light to filter between floors and through the gaps in its cantilevered wooden treads.

A large bedroom is located on the ground floor, alongside a family bathroom and a walk-in closet.

Apollo Architects & Associates now has offices in Japan, China and South Korea. Other projects by the firm include a narrow house on a Tokyo high street and a combined house and hair salon.

Photography is by Masao Nishikawa.

Project credits:

Architect: Apollo Architects & Associates
Structure engineers: Masaki Structures, Kenta Masaki
Facility engineers: Naoki Matsumoto
Construction: Yamazen Kensetsu