A metal roof completely surrounds this house by Japanese studio Suppose Design Office, sheltering terraces and a garden so that residents can use these spaces all year round (+ slideshow).

Located in Tochigi Prefecture, House in Utsunomiya is covered in clad in strips of white-painted Galvalume – a coated steel sheeting – and lined in Japanese cedar wood.

Its huge roof features a series of cutaways that allow natural light to enter both the rooms and the terraces.

This roof was the starting point for the design. Once its sloping form was developed, Suppose Design Office inserted a series of simple rectilinear volumes underneath to create three floors of rooms.

Most rooms feature large windows that slide open, with some set into the straight walls and others puncturing the sloping roof. These are positioned carefully to offer some privacy from neighbouring houses.

"We believe that to design architecture means to create space," said the architects, who also recently completed a house that hides a garden below an oversized shingled roof. "At the same time, it means dividing inside and outside clearly."

"If this means that the outside becomes inside by the existence of the roof, we could say that means we are able to spatialise the site."

A narrow gravelled terrace runs along one side of the house and adjoins a wood-lined living space at ground level. A balcony is located on the first floor, directly above, while a terrace is set into the tip of the roof.

These partially covered spaces are intended to break down the distinction between the interior and exterior portions of the house.

"Between the volume of the house and the roof, there is an ambiguous middle area, it can be said to be both inside and outside, in which this middle area connects the inside and outside gradually," explained the studio.

"The middle area creates shade, and works to thermal environment. Also, it makes an opportunity to use outside actively," it added.

"A family can have an open-air meal, or use the garden on rainy days, which changes the atmosphere of the daily life inside an ordinary house."

A pair of bedrooms, bathroom and storage room are arranged around the balcony and an atrium on the first floor.

The master bedroom overlooks the open-plan living space below, while the second room is positioned next to the balcony.

A flight of steps leads up to the final terrace, which is set in the apex of the roof.

Suppose Design Studio was established by architects Makoto Tanijiri in 2000, and has offices in Hiroshima and Tokyo.

The studio since has completed dozens of houses, including one with sunken rooms and see-through walls and one with translucent polycarbonate walls. Other projects include a cafe with the ground surface of a car park and a seafront cycling hotel.

Photography is by Toshiyuki Yano.