A spiral staircase breaks the linear geometry in a Japanese house designed by Kazunori Fujimoto Architects & Associates, which is made nearly entirely of concrete.

The house is built for a couple and their four children and sits at the base of Mount Rokko, a popular tourist destination, in the Hyōgo prefecture.

The studio designed the home with minimal openings to block out sound from a nearby road and orientate views out to the picturesque scenery.

The house is split across two floors within two cuboidal volumes.

The spiral staircase is the first feature in view at the end of the corridor. It was formed from a CNC-routed mould, transported to the site and cast in-situ as the house's finishing touch.

Designed as the central feature of the home, Kazunori Fujimoto Architects & Associates gave spiritual significance to the staircase as a yorishiro. In the Shinto religion, this term is allocated to an object that will draw spirits in with a physical vessel to occupy.

"The staircase goes beyond its function and becomes the yorishiro, which symbolises the unity of the family in this house," explained Kazunori Fujimoto, founder of his eponymous studio.

The house's internal layout reflects its linear exterior, as the studio opted for thick horizontal and vertical planes for ledges and walls to express "spatial purity".

These are contrasted by the curved lines of the staircase, which aims to soften the rigidity of the interior.

The kitchen and living area occupies the immediate open space inside the same volume as the entrance and stairs.

Completely open plan, it provides a space for all six members of the family to gather together within the small-sized house.

An upper mezzanine level above the entrance can be accessed up a steel ladder above a large window.

Windows throughout the house were placed high on the house's walls to maintain the family's privacy from their neighbours and replace views with the mountainous scenery.

Located near Frank Lloyd Wright's Yodokō Guest House, the studio balanced the number of openings and enclosures to block out noise from the popular tourist spot.

The walls and windows have rotational symmetry from the room's centre, which according to Fujimoto, is named the "windmill style" layout in Japan.

"The wall surroundings safe living areas while windows make it open at the same time," he explained.

Despite its importance in the house, the studio designed the staircase to take up as little space as possible in the corner.

This decision allowed for connective circulation space underneath the spiral, which leads to the master bedroom in the second volume.

The first floor is divided into four equally sized bedrooms by two partition walls. Standing at the centre of the plan, they leave a 550-millimetre space around the perimeter for the children of the house to snugly pass between.

A large opening perforates three of the volume's facades. As these are placed in the centre of each wall, two bedrooms are able to share one opening.

Fujimoto is no stranger to delicate concrete spiral staircases, which he employed previously in House in Akitsu. Meanwhile, Hildebrand employed one at a larger scale for the Hapimag office in Switzerland.

Photography is by Kazunori Fujimoto.

Project credits:

Architect: Kazunori Fujimoto Architect & Associates (Kazunori Fujimoto, Andrea Ferri)
Structural engineer: Eiken Structural Consultants, Eiichi Tsumura
Construction team: Yamamoto Koumuten