Hong Kong is way behind other Asian cities in designing green buildings, a consultation document to be released this month shows. In the document, by the Council for Sustainable Development, the Tokyo government is said to have successfully promoted green roofs within four years. More than 54 hectares of rooftops had been greened by 2005 since initiatives launched in 2001, increasing at a rate of 20 hectares per year - equivalent to about 80 soccer pitches. The mainland building code requires developers to provide greenery covering no less than 30 per cent of all residential developments in new districts and 20 to 25 per cent in old districts. But the effectiveness of some so-called green features in Hong Kong is doubtful. These include sky gardens, mail delivery rooms, clubhouses, larger lift shafts, and voids over entrances to lobbies and car parks. Tree expert Jim Chi-yung of the University of Hong Kong said few sky gardens in Hong Kong were of good quality. They were often occupied by a few potted plants in poor condition. Those at high level were often underused because of windy conditions. 'The government should set rules for sky gardens exempting them from the gross-floor-area calculations to ensure their quality,' Professor Jim said. He suggested that a minimum 75 per cent of such gardens should comprise greenery, adding that they should not be higher than the 10th storey to ensure a comfortable environment in terms of wind. Flexibility should also be given to the floor heights of gardens so that sunlight could reach their inner areas. 'Green buildings in Singapore return nature to the city,' he said. One example was residential development Newton Suites in the Novena district. Apart from trees in sky gardens, the building's facade was covered with greenery and the ground-level car park was shielded by a mass of trees to absorb exhaust emissions. Ben van Berkel, an internationally renowned architect who designed the Mercedes-Benz Museum in Stuttgart, told the Post that an architect was a fashion designer who dressed up the city's future. 'However, architecture is not found in its shape, but how we organise our lives.' He said the way he designed the Stuttgart museum had made visitors feel like owning the collection of cars displayed. He also purposely made the museum less compartmental to save on construction costs. 'Sustainable architecture is not only about being green. It's about attainability. Whether they are affordable,' he said.