World famous for its skyscrapers, Hong Kong's bustling urban landscape now faces a shortage of good air ventilation.

Medical experts and environmentalists have expressed concern over the proliferation of the concrete jungle creating a "wall effect", blocking the flow of fresh air.

Many residential high-rises are built along the waterfront where the sea views are a prime real estate commodity. However, for many residents living in apartment buildings further back, the availability of fresh sea air has become less of a right, and more of a privilege.

According to a study conducted by community group Green Sense, 104 out of 138 private residential estates developed over the past 10 years had met three or more criteria of the wall effect.

The criteria included less than 15 meters' space between buildings, building height over 35 storeys, building facing prevailing wind and the existence of shorter buildings behind taller ones.

The green group was concerned that the problem would worsen as the plot ratio, which defines the total floor area of buildings permitted to be constructed on a site, for 36 old district redevelopment projects had been increased by five to 12 times. The higher the plot ratio, the taller the buildings are.

For example, the redevelopment project in Tsuen Wan would result in two 45-storey buildings, while most of the existing buildings in the old districts are only four to six-storeys.

Hong Kong Medical Association council member Alvin Chan said the ventilation of areas behind tall buildings would be affected. He expressed concern that the temperature of these areas would go up, making it stuffy and uncomfortable for the residents.

The Hong Kong Observatory had found that the wind speed in some urban areas had dropped by 0.57 meter a decade from 1968 to 2005. The average wind speed of remote Waglan Island in October was 17.6 kilometers per hour, while that in the urban areas like King's Park was only 7.1 kilometers per hour.

"The spread of flu, respiratory and heart disease will also be more serious in cramped areas with little wind," he said.

"The pollutants will not be easily dispersed in these areas."

The Housing, Planning and Lands Bureau and the Environment, Transport and Works Bureau recently jointly issued a notice that listed ventilation as a main concern for redevelopment and large infrastructure projects.

The government would also encourage the private sector to voluntarily assess ventilation before starting building projects, and also restrict building heights in certain areas.

Green Sense chairman Roy Tam Hoi-pong said the government should make the notice a law, making ventilation a compulsory concern for infrastructure projects.

"Only making it a voluntary consideration is not enough," Tam said.

Apart from limiting building height and plot ratio, Tam suggested making it a compulsory requirement that the distance between buildings be at least 15 meters.

Bernard Lim, a Town Planning Board member, said developers should create models before starting building projects. The model will be used to test the ventilation, and find out whether the space between buildings and the scale of the projects should be maintained.

(China Daily April 3, 2007)