As Japan’s cities get denser, could greener rooftops replace lost gardens?

While Japan’s population shrinks, its cities are becoming denser, Tokyo in particular. In 20 years, the city’s 23 wards have added more than 1.2 million residents, bringing the population to 9.8 million. Density now stands at 15,600 people per square kilometer.

The increased density has mostly come in two forms. The first is the construction of residential tower blocks containing dozens, if not hundreds, of units. The second is the subdivision of house-and-garden lots, where a house is knocked down, the garden cleared and two or more new homes are built in its place.

The loss of these gardens can be keenly felt by the surrounding community. A garden is private property but still serves a public function. Anyone who regularly walks by enjoys its dance with the seasons. The birdlife it attracts is a communal asset.

The two or more residences squeezed onto a former single lot are largely uniform in design. They have a carport or garage, measure around 6 by 5 meters in area and are three stories high. Some have access to their flat roofs. Some do not.

Rooftop gardens could give residents outdoor space while bringing greenery into the views of neighboring buildings. | JOHAN BROOKS

Yet every one of these flat roofs presents an opportunity to bring back some of the greenery lost below. Few homeowners take it. In urban Japan, rooftops are rarely treated as spaces for living.

Why we stay below

Why are these spaces so rarely used? The question was at the heart of a recent symposium organized by the Norwegian Embassy in Japan and the Norwegian architectural firm Snohetta. It brought together Kjetil Thorsen, a founding partner of Snohetta, and Richard Wood, its managing director for Asia. Snohetta is an acclaimed global architectural firm that routinely wins major design competitions. It is currently constructing the Shibuya Upper West Project, west of Shibuya Station.

The symposium also featured husband-and-wife architects Takaharu and Yui Tezuka, leading practitioners in the design of usable roof space. Their best-known project is Fuji Kindergarten in Tachikawa, Tokyo, where the entire oval roof serves as a play deck for pupils. The design has been highly influential, both architecturally and educationally, and is frequently cited for its impact on children’s educational and social development.

Fuji Kindergarten in Tachikawa, Tokyo, was designed by architects Takaharu and Yui Tezuka, with its oval rooftop forming a central feature of the school. | KATSUHISA KIDA/FOTOTECA

The rooftop serves as a play deck, giving children space to run, climb and play outdoors above the school. | KATSUHISA KIDA/FOTOTECA

Some of the reasons Japan’s rooftops are underused are psychological. People worry about noise complaints from neighbors or those living in the apartment below. They may also feel self-conscious about being visible from the windows of surrounding buildings.

Other concerns are more practical, including the fear that rooftop fittings and furniture could be blown away during extreme weather. Thorsen, Wood and the Tezukas all agreed that this fear is unfounded. Professionally installed roof fittings can withstand a typhoon. For nonfixed garden furniture, no more care is needed than with a temporary washing line on a balcony.

Thorsen added that soil and vegetation absorb significant qualities of water. This reduces the risk of damage from water runoff, an increasingly pertinent concern in a Japan inundated by rain this summer.

Designing the roof

Architects have also played a role in the underuse of rooftops. Most are left as little more than bare, flat spaces once construction is complete. This is particularly visible in tiered suburban apartment buildings, where some floors have one fewer apartment than the floor below. The arrangement actually creates a rooftop terrace for the apartment on the tier above, but these spaces tend to go unused. Left bare, they are also unappealing.

Drainage pipes and other infrastructure can leave apartment rooftops feeling more like utility spaces than outdoor rooms. | JOHAN BROOKS

Takaharu Tezuka suggests that simply adding a permanent bench and planter box to these rooftops could fundamentally change how they look to those around them. The spaces are typically accessed indirectly through a side balcony, so Yui Tezuka suggested that placing an access door in the middle of the wall facing the rooftop could also change how people see them. It would make the outdoor area feel like an integral part of the apartment. The loss of wall space required for the door would also ensure that buyers were genuinely interested in using the space.

For the multiple homes built to replace a single house and garden, a simple bench, planter box and awning could likewise be included as standard features, encouraging owners to use their rooftops for more than hanging laundry.

Fear from above

A further source of unease is the fear of being unable to escape from an elevated position during a natural disaster. Buildings are far more fire resistant in present-day Japan than they were in the past, says Hiroaki Saito, a former writer and longtime Japan Times columnist, but perceptions can persist. The country is prone to earthquakes, and fires have historically accompanied them. Buildings have routinely burned down.

Concerns about noise, privacy and extreme weather are among the reasons rooftop gardens remain uncommon in Japan. | JOHAN BROOKS

In one of the most famous fires involving a single building in 20th-century Japan, the rooftop was central to the story. In 1931, the Shirokiya department store in Nihonbashi was set ablaze, and many staff evacuated to the rooftop. Trapped by the flames, they were encouraged to jump into netting that the fire brigade had set up. The female sales staff were wearing kimono and did not wear Western-style underwear. Many are said to have hesitated to jump for fear of exposing themselves and ultimately perished.

There remains considerable debate about the veracity of this story, with many contending that the underwear narrative is simply an urban legend. But from the standpoint of perception, that hardly matters. The Shirokiya fire is a famous example of urban dwellers perishing after becoming trapped on a rooftop. As Saito reminds us, perceptions are resilient. They can take time to change.

A different way to see the roof

In 2010, the Organization for Economic Cooperation and Development (OECD) named Fuji Kindergarten the winner of its Exemplary Educational Facilities competition, which attracted 166 submissions from 33 countries. Indeed, the building is well-known among architects but remains largely unknown to the Japanese public.

In Oslo, there is a prominent landmark building whose rooftop is so well used that it has become part of the city’s public life: the Snohetta-designed Oslo Opera House, which sits on the edge of the Oslofjord.

The roof of Oslo’s Opera House, designed by Snohetta, rises gently from the waterfront, creating an urban space where people can walk, gather and enjoy the city. | © JIRI HARVAN

The roof of the opera house can be accessed from ground level and has essentially become an urban park. Oslo residents use it daily for a wide variety of purposes. It can function as an amphitheater for outdoor performances, and people have mountain biked, skateboarded and skied down it. Another prominent Snohetta project with a pedestrian-friendly roof, the Shanghai Grand Opera House, is scheduled to open in October.

“The Oslo Opera House redefined ‘the roof’ as a space for public life,” Richard Wood tells The Japan Times. “We believe the Shanghai Grand Opera House will take these ideas to new heights.”

The Shanghai Grand Opera House features a pedestrian-friendly rooftop that extends the building’s public space into the surrounding city. | TIAN FANGFANG

And Tokyo isn’t without its own rooftop experiments. Miyashita Park has put lawns, walking paths, skateboarding and bouldering on top of a commercial development. In Ginza, the Ginza Honey Bee Project has turned commercial rooftops into apiaries, producing local honey while helping to green the city.

Perhaps the challenge for urban Japan is not finding more space, but recognizing how much space is already above us.