By Junko Kawakami
In Tokyo, one of the world's most overcrowded cities, land is expensive and it is always difficult to find and buy an ideal plot. So, building houses on difficult patches of land is not uncommon. At the same time, such challenges encourage Japanese architects to create impressive and ingenious buildings. This house on a tiny triangular plot in Horinouchi, designed by Architect Kota Mizuishi, of Mizuishi Architect Atelier, is an excellent example.

Houzz at a Glance

  • Who lives here: A couple and their two young daughters
  • Location: Tokyo, Japan
  • Structure: Wooden, two storeys
  • Site area: 52.1 square metres
  • Building footprint: 29.1 square metres
  • Total floor area: 55.2 square metres
  • Architect: Kota Mizuishi of Mizuishi Architect Atelier
  • Structural design: Ken.Nagasaka Engineering Network
  • Builder: Hirano Kensetsu

The house is the residence of a furniture designer, his wife, who works from home, and their two young children. They had previously rented an apartment in the area, but their dream was to build a house. One day they were drawn to Mizuishi's office nearby. They didn't have a large budget but wanted to build a house in the same neighborhood. Mizuishi and the homeowners looked for a site and finally found this very small and narrow piece of land along the river.

The site is a triangular plot sandwiched between the Zenpukuji River and a little lane. However, narrowness wasn't the only challenge the lot presented.

Article 43 of the Japanese Building Standard Law stipulates that every property must be connected to a road at least four meters in width, either directly or by a driveway, in order to allow access for emergency vehicles. However, this was not the case here, as the lane next to the house is less than four meters wide. It was therefore necessary to contact the city and the surrounding neighbors, get a special permit and fit the design as much as possible to the regulation.

A buyer for such a piece of land is hard to find, so, luckily for the owners, it was offered at a considerably lower price than the market average for the area. The current homeowners asked Mizuishi if it would be feasible to build a home there at all. After considering how much living space they would be able to extract from the site, they concluded that it could be done, with some ingenuity. The project began to take shape.

With such a narrow structure, however, there is the danger that the house might fall sideways in the event of an earthquake. Then again, too many pillars would have diminished the interior space. Instead, the structure was reinforced internally with small, load-bearing walls, which also help divide the interior into zones (pictured in later photos).

Due to budgetary constraints, the architect chose a wooden structure.

The house now nestles between the small lane and the river-bank promenade. "We cut off the sharp corners of the site's triangle and placed windows on those sides, so we can see the river from three sides of the house," the owners say.

The part of the ground floor that appears to be indented allows for a parking space. "I was a bit surprised when I was asked to make space for a car on this tiny lot. It's limited to a mini vehicle, but I was able to make room here," Mizuishi says.

Rows of ceramic siding cover the ground floor, while the first storey is encased in maroon-coloured galvanised-steel plates, oriented vertically. The transitions of texture and colour make the house look lighter and less dull than if it had had a monotone exterior. The switch to the different finishing material on the overhanging part of the second floor also emphasises that area.

Additionally, despite the steepness of the roof, the house lacks rain gutters. It's a radical solution that makes it appear as though the roof and walls are one. "It's quite courageous not to have a gutter, but we have U-shaped grooves on the outer perimeter of the foundation, so we won't have problems with rainwater drainage," Mizuishi says.

Because the ground of the site is lower than the riverside promenade, it is possible for passers-by to look into the ground floor. Therefore, the main living area is situated on the first floor, which also allows the family to see the scenery of the path and the river. These photos show the house immediately upon its completion, but the trees have since matured, partly blocking the pedestrians' sightline.

Given its location along a river, it is possible that floods may affect the site. For this reason, the ground floor was raised 60 centimetres above the ground, and 24-hour underfloor ventilation was implemented to prevent dampness. A sliding door was installed on the entrance, approached by moveable steps.

Additionally, the entrance threshold is 10 centimetres in height and depth, and consists of concrete clad in stainless steel. The homeowners wanted to make sure any flood prevention measures would be as unobtrusive as possible.

The ground floor houses an entrance area, a bedroom and a bathroom.

The entrance meets a mortar-finished concrete floor as well as the stairs, which lead up to the living room, dining room and kitchen. The large shoe cabinet featured on the right of the photo floats above the floor. This is to ensure that it doesn't make this part of the house appear even smaller than it is. The spot under the staircase is taken up by a washing machine and storage. No space is wasted.

The bedroom's solid-wood flooring is made up of Japanese cherry birch, which "is good quality and reasonably priced. Even though the budget was limited, I wanted to use high-quality materials as much as possible," Mizuishi says. The antique piece with small drawers is a family favorite – they owned it long before they moved into this house.

The bedroom, where the whole family sleeps, can be separated from the mortar-floored part of the storey by a curtain suspended from the ceiling. There's a closet behind the bed, which is, again, hidden by curtains instead of doors. On top of keeping costs down, the soft, translucent material ensures a feeling of openness, even when it's closed.

A glass wall separates the toilet and the bathroom. The walls have been painted in several shades of white to create a feeling of spaciousness.

Upstairs, a spare room is currently being used for storage. It is unobtrusively separated from the rest of the floor by the load-bearing walls mentioned above.

The lower shelves on the lane side of the living-kitchen-dining room (on the left in this photo) were made to accommodate the family's love of music: they fit their audio equipment and CD collection. The computer desk in front is a workstation for the woman of the house, who works from home. A bench, installed on the river side, serves as a sofa and its bottom compartments as storage. At night, curtains maintain privacy.

As there is a loft directly above it, the living room ceiling isn't very high. However, thanks to the large windows on both sides, one never feels overshadowed.

The bay was built at such a height as to align the window's exterior sill and the surface of the bench seat. When the window is open it creates a sense of depth, and the combined surface can also be used as a terrace. This was another ingenious way of making effective use of limited space.

The sharp corner of the triangle hosts the kitchen and dining room.

Despite how small it is, the kitchen has a relaxed air thanks to the height of the sloped ceiling, which adheres to the shape of the roof. The ceiling's dimensions are emphasised by the pendant light. The Nakajima Tatsuoki Lighting Design Laboratory designed the lighting, which consists of recessed lights throughout most of the house. These highlight the quality of the space without being overbearing.

There is a loft, less than six tatami mats (9.7 square meters) in size, above the living room. It's a fun, creative playroom for children, where one can still feel connected with family members in the kitchen and dining room. There are two load-bearing walls on each side of the loft.

Light enters the loft through skylights. The one on the south side was added after construction had already begun, at the last possible opportunity to introduce a new opening. Besides letting light in, it provides the room with fresh air.

Since it faces the south, however, there is also a risk of overheating the room. Still, the daring installation of the skylight on this side allows the family to take in views in three directions from the loft, as they are able to see the river from the windows on both sides of the house and look up at the sky from the skylights. It gives the feeling of a connection with the outdoors.

"When I start to design, I definitely want to create something of value," Mizuishi says. He has certainly done that in this house in Horinouchi: by reading the merits of a quirky site that no one else wanted, he succeeded in designing a comfortable living space.

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