A secluded passage extends along one edge of this house in Japan by Alts Design Office, bringing natural light into the interior (+ slideshow).

Japanese studio Alts Design Office, whose previous projects include a house filled with pointed doorways and openings, designed the two-storey Kusatsu House for a site beside a car park in Shiga.

The close proximity of neighbouring residences and apartment blocks made it impractical to add glazing on the south-facing facades, so architects Sumiou Mizumoto and Yoshitaka Kuga instead created an open-air passageway along the north-western wall.

"A house with southern exposure is not good because the client wants to secure the privacy," explained the architects.

"Therefore, we arranged the exclusive path inside of the house. We gave importance to designing an outside space in the inside space, and produced a diverse and interesting space," they said.

Flanked by a windowless concrete wall, the passageway is glazed at both ends and has a skylight overhead, allowing daylight to permeate the building throughout the day.

A traditional Japanese tatami area is located within the space, alongside a small rock garden. Glazed doors open the passage to the open-plan living room, dining area and kitchen, which takes up most of the ground floor.

"We didn't separate into inside and outside of house simply," said Mizumoto and Kuga. "By doing so, we brought a feeling of strangeness in a good sense."

The room features simple furnishings that define the different areas. A wooden dining table offers seating for four people, while a selection of plants sit beside the walls and a low white wall defines the kitchen.

Wooden panel flooring runs throughout the interior. Chunky timber surrounds doors and windows, while a steel-framed staircase leads up to the first floor.

This upper storey is divided up into four rooms. The largest is the master bedroom, which leads out to a balcony positioned above the passageway.

Two smaller rooms accommodate the family's children, while the fourth space is a bathroom, with a separate WC alongside.

Photography is by Yuta Yamada.