Roof Gardens

Roof Garden

A couple of weeks ago, I wrote about Muji’s attempt to resolve their customers’ desire for green space whilst maximizing their development’s density (and profitability). Today, I am covering an alternative solution to Japan’s lack of green space.


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Take a look at an aerial view of Tokyo and consider what proportion of land is occupied, by tiled and concrete roofs. The city has experienced a 3 degree rise in temperatures in the last 100 years due to its heat island effect. This warming could be mitigated if new and existing buildings were fitted with green roofs. Providing both access to light and rainwater, planting the roof seems a logical solution to improve Japan’s crowded cities.

Cruising through the roofscape on one of Tokyo’s elevated railways, you’ll see there are already a lot of buildings with balustraded flat roofs, yet these seem largely underutilized save for perhaps drying laundry and futons. Some Japanese office buildings already have green roofs (a few even support small farms). Some, like Fukuoka’s ACROS building and the Roppongi Hills Keyakizaka in Tokyo are remarkable examples of urban green roofs. A recent law mandates green roofs over 20% of new 1000sqm+ schemes. However, the housing sector lacks similar initiatives.

The sustainable benefits of green roofs are undisputable. Planting vegetation on rooftops not only helps mitigate heat from solar absorption, it insulates the home. Plants and soil absorb rainwater, reducing runoff. Intensive green roofs (that support a wide range of plant species) also form urban habitats for natural wildlife, promoting biodiversity within the city. Many Japanese are avid vegetable gardeners and their own rooftops would be an ideal (not to mention convenient) place to grow their own food (like the couple in the video below does).



Design is the critical factor in making the roof garden feel like a sheltered extension of the home. Raising the walls higher will protect the garden from wind and overlooking, whilst window-like openings frame views and preserve the integrity and composition of the overall building form.

The added weight of soil, plants, and people requires additional structure of course. Moreover, an additional stairway is required to access the roof. Drainage across an inhabitable flat room also requires special solutions (although more than one company is already on the case).

Obviously, the luxury of a roof garden does not come without additional cost. If you are a Japanese home owner, however, the question is what is access to plants, sunlight, and fresh air (basic ingredients of life) worth?

A Final Caveat:

It is not really accurate to say that Japan should learn about green roofs from the West. No country can really lay claim to this idea and grass has probably sprouted on the thatched roofs of Japanese farmhouses since ancient times. As stated above, Japan has a number of notable green roofs (both large offices and houses).  That said, Japan (and the rest of the world) is still somewhat behind Europe in this regard. We can all agree, however, that the world needs more green roofs – particularly Japan.


(an intensive green roof in Japan by RA Architects)

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