Katsutoshi Sasaki + Associates built this unusually skinny house on a three-metre-wide site in a residential district of Aichi Prefecture, Japan (+ slideshow).

To accommodate for its narrow width, the two-storey Imai house stretches out along most of the 21-metre-long plot. There was no room for corridors, so the interior is arranged as a simple sequence of rooms, one after another.

Japanese studio Katsutoshi Sasaki + Associates adapted the proportions of each space to suit its function, so the living room features a double-height ceiling while the children's sleeping space is a 1.3-metre-high loft.

"We adopted a way to construct a house by reinterpreting scale, natural light, and the use of each room," said the architects.

The ground floor is recessed to make room for a sheltered driveway at the front of the plot. Here, a wall slides open to lead into a kitchen and dining room that takes up most of the ground floor.

A wooden staircase spirals up toward the living room, located at the centre of the first floor, while a second set of steps angles up to meet a secluded roof terrace at the front of the house.

This terrace is fronted by large panels of glazing, which help to bring natural light and ventilation into the living room from above.

There wasn't enough space on the site to create a separate garden, so the architects also added a small indoor patio at the rear of the ground floor, featuring a wall that slides open.

A long narrow space between the living room and master bedroom functions as a children's room. The sleeping space is raised up from the floor and includes an assortment of small square windows, while built-in shelves create a study desk along the opposite wall.

According to the architects, the rooms could become interchangeable. "The space setting becomes neutral; you can sleep, dine or relax whenever you like. For example, dining in the inner garden may be more enjoyable than in the dining room," they said.

Photography is by the architects.

Here's a project description from Katsutoshi Sasaki + Associates:

Imai

A house built on a narrow strip of land of 3m wide and 21m long. For this ground that looks too long and tight, we adopted a way to construct a house by reinterpreting scale, natural light, and the use of each room. Instead of setting one concept to design it, we made five specific proposals.

1: Balancing of scale and light

Height of each room is adjusted according to the number of users and the use of the room. For example, children's bedroom is 1.3m high while the living room is 4.4m. The room used by one person has limited natural light while the space people gather is much brighter. Balancing of scale and light brings a character to simple one room.

2: Exterior on the edge

The ground was too narrow to allow any space for garden, so we set an inner garden at the end of the ground floor and a terrace on the north end of the second floor. High window in the living room is designed not only to let in light, but also to provide ventilation route in summer to discharge the heat accumulated up on the ceiling plane.

3: Dismantling

By dismantling living room and dining room, we avoided large area concentrated to one place. As these spaces that have public nature are dispersed, lines of flow work effectively. Also, by de-concentrating the factors required to children's room such as sleep, storage or study, we can reduce the floor space of children's bedroom while sharing space for other functions of storage and study by entire family.

4: Unrestricting

We suggested the way of living to utilise the space other than wet areas (kitchen, bathroom etc) without restricting its purpose. In some, the space setting becomes neutral; you can sleep, dine or relax whenever you like. For example, dining in inner garden may be more enjoyable than in dining room.

5: Overlapping

By overlapping multiple uses on one space, efficiency of floor space is improved. Corridor as desk space, inner garden as dining or guest room, and so on. This narrow and long building that could be described as all lines of flow, is designed as functional, effective and liberating space by applying these operations.

Project name: Imai
Location: Okazaki, Aichi, Japan
Site area: 71.19 sqm
Built area: 42.64 sqm
Total floor area: 69.49 sqm
Type of construction: wooden, steel
Exterior materials: Metal finish
Interior materials: paint finish
Design team: Katsutoshi Sasaki + Associates
Structure company : Tatsumi Terado Structural Studio
Construction company: Inoue construction Ltd.