Green Roofs in Tokyo, Japan and Asia

Electricity demand in Japan peaks during the summer as a result of air conditioning requirements. The Japanese government has therefore given green roofs a high priority at national and city level as a primary means to reducing building energy use. As a result, Japan is one of the major global centres of green roof implementation, with a particularly famous example being the Prefectural International Hall in Fukuoka City.

Tokyo

The average annual temperature has increased by 3°C in the last century – mostly due to the urban heat island effect. Consequently the city has introduced policies that require green roofs to be installed on 20% of all new flat roof surfaces on public buildings exceeding 250m2, and 10% of all flat roofs on private buildings exceeding 1,000m2. This results in the construction of around 50,000m2 of green roofs annually.

It has been estimated that if half the roofs in the city were planted with gardens, daytime summer temperatures would fall by 0.84°C, saving 110 million Yen, approximately £722,244, in air conditioning costs.

Singapore

In 1996, a technology transfer agreement was signed to bring the German green roof concept into Singapore, and assess its suitability to tropical conditions. In 2003 the first large-scale extensive green roof was installed at HDB’s Pilot Project in Edgefield Plains, Punggol.

Another high profile example of green roofs is Fusionopolis, a science and technology powerhouse for Singapore. This integrates 13 roof gardens amounting to some 3,000 m² of sky greenery, including 6 large-scale thematic ones on the 5th, 18th and 21st storeys. They serve as the ‘green lungs’ and social pockets for the office and lab staff. The highest roof garden is located at the 24th storey.

Energy simulation programmes have been conducted on a hypothetical 5-story commercial building with a roof garden in Singapore11. The results showed significant savings on energy in terms of:

• approximately 15% of net annual energy savings;

• up to 80% reduction in the peak cooling load can be achieved, resulting in the possible downsizing of air-conditioning systems and thereby savings in capital investment; and

• a reduction of peak Roof Thermal Transfer Value (RTTV) of up to 80% making roof gardens as a viable substitute for roof thermal insulation.

In addition, Singapore is a thriving Asian city-state with miniscule farmland resources, and a survey of the food-from-the-roof opportunity found it may be able to devote up to 1,000 hectares of its urban rooftops to fresh vegetable production, now mostly imported at a considerable fossil fuel energy cost.

Hong Kong

In Hong Kong Intensive Green Roofs are already well-established in the form of podium gardens as they provide what Hong Kong needs most – valuable functional open space for human use. Extensive Green Roofs, on the other hand, are better-suited to retro-fitting projects which have their own technical constraints, and are not yet well-established in Hong Kong.
Despite Intensive Green Roofs being well-established, a consolidated approach to green roof techniques and standards is still needed.

It appears that no information exists on the percentage distribution of green roofs in Hong Kong. Existing government policies and standards influence the creation of intensive green roofs in the public and private sector in both direct and indirect ways.

Joint Practice Notes 1 and 2 (JPN) are designed by Government and set out the initial incentives that Government is providing to encourage the incorporation of ‘green’ features, and give guidance on how to apply for them under the Buildings Ordinance, the Lease Conditions and the Town Planning Ordinance, as appropriate. JPN 1 refers to residential developments and JPN2 refers to commercial developments.

Furthermore, the purpose of JPN116 is to provide incentive to private developers to include amenity features that are not a statutory requirement but which enhance the quality of life for residents and users.

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