Behind a simple concrete exterior, this house by Japanese architect Tsubasa Iwahashi contains a complex arrangement of rooms connected by three different kinds of staircase (+ slideshow).

Named Relation, the house was designed by Osaka-based Iwahashi to create a series of separate spaces that are visually connected to one another.

The aim is for the resident family to feel connected to one another when occupying different rooms.

"Wherever they are in the house, they can feel a sign of the family," explained the architect, whose other house designs include one planned around a dining table and another with a stripped-back interior.

"[Residents] are connected to each other, but the house has a moderate sense of distance," he said. "They can spend time together or alone."

The property is located in a suburban residential area in Hyōgo Prefecture. It is two storeys high, although its interiors spaces are arranged across multiple floors.

The ground floor is level with the street, and slightly sunken down from the area to the rear of the site. The upper storey is split into two levels, creating a hidden storage area under one of the floors, and there is also a loft room in one corner.

The first of the house's three staircases is a traditional set of wooden stairs that extend up from the reception to a piano room.

From here, a more minimal set of wooden treads extends up, supported by a diagonal wooden beam.

The final climb is provided by a ladder that leads up from a multi-purpose library room to the loft.

It is also wooden, but has been painted dark grey to allow it to stand out. One of its supports extends out to become the first piece in a series of angular struts, which frame one end of the loft.

The family's living, dining and kitchen areas are are located in one open-plan space on the ground floor. Glass doors allow residents to open the room out to a wooden terrace platform.

"On the terrace, the conversation with the neighbours begins, and they will build a relationship with the town," said Iwahashi. "Gradually, the house becomes part of the scenery of the town."

A bathroom and laundry area are tucked away on one side of the living space behind a wall of bare plaster. A small niche shaped like a mouse hole creates a space for plug sockets.

Engineered wooden flooring runs throughout the house, apart from at the entrance, where a sunken tiled surface extends in from outside. Wooden ceiling beams are also exposed in every room.

Plywood was used to build several furniture elements, including a frame around the piano and a series of bookshelves that double up as screen walls. There are also golden details, both on lighting and windows.

Relation was completed in September 2015, and has an overall floor area of 111 square metres.

Photography is by Yoshiro Masuda.