Japanese house extension by Container Design is arranged around a covered courtyard

This addition to a house in Kudamatsu, Japan, features an oversized pitched roof and a covered courtyard surrounded by arched openings.

The two-storey building is positioned close to the client's existing family home and was designed by architect Takanobu Kishimoto of Kobe-based Container Design to provide additional living spaces – including a kitchen, dining area, sitting room, traditional tatami room and a study.

The main entrance opens onto a double-height space described by the architect as an indoor courtyard, with a floor covered in pebbles and paving slabs that form paths across its surface.

The buildings sit on a plot separated from a busy road by a wall with an opening and no gate, so the architect was asked to create a structure that encourages the children to play in the area between the two buildings and away from the road.

"Their main hope is that they can pass between their family home and their children can run around inside and outside the house," explained the architect.

A yard between the buildings is planted with trees and shrubs that create a clear route from the end of the new structure to the side of the existing building. A window and porch in the addition are arranged facing the main house to create a visual connection between the two.

The opposite side of the new building presents a solid white facade to the street, partially blocking the view of the main house.

"The family home is seen from the prefectural road, therefore the new house was made near that road," said the architect. "As a result, I thought that the house will be made like a gate and fence in the site."

The relationship between the two parts of the property is emphasised by the elongated sloping roof of the addition, which echoes the tiled pitched roof of the house behind it. An opening in the roof creates an enclosed terrace on the road-side of the building.

Protrusions that angle in opposite directions to the main roof structure create extra space for rooms on the upper floor.

The long elevation facing the car parking area in front of the main house is interrupted by two arched doorways; a normal sized one covered by a curving canopy, and a smaller one for children.

The larger entrance opens onto the covered courtyard. A staircase positioned diagonally across this wood-lined space ascends to the upper floor, where two spare rooms, a study and a terrace are located.

The space is surrounded by wooden walls punctuated by arched openings that lead to other rooms, or frame windows that fill the space with natural light. It is covered by a gently arched ceiling.

This space and a study on the mezzanine level at the top of the stairs both feature exposed wooden walls. The rest of the interior walls are painted white to create neutral spaces that make the most of the available light.