1 Roof garden to keep station cooler
Nickkita Lau, The Standard 27 September 2007

A HK$2 million roof garden at the old Tai Po Market railway station is being used to reduce the temperature inside the station by at least two degrees Celsius.

University planners have found that the surface of a bare rooftop can hit 54 degrees Celsius on a hot summer's day. But the temperature drops to 32 degrees when a green rooftop is added.

The 2,000-square-meter rooftop garden is part of the station's HK$79 million renovation project, which started in June last year.

By the time the garden is in full bloom, the Kowloon Canton Railway Corp expects the greenery to reduce the station's indoor temperature by two degrees Celsius, keeping it around 26 to 28 degrees.

The KCRC says it hopes to improve the quality of the environment and contribute to sustainable development by incorporating more green elements.

The company chose Tai Po Market station because its roof is very visible to passengers standing on the platforms, said KCRC infrastructure and building general manager Fung Wing-yiu.

Hong Kong University's Department of Geography planned the garden, with the KCRC funding the research program. Professor Jim Chi-yung said there are successful examples of roof gardens in Europe but building it in a subtropical Asian city is unprecedented.

"A rooftop garden could extend the life of the roofing membrane two to three times," Jim said. "There is an extreme case in London - a roof garden built 70 years ago at a department store has a roofing membrane still in perfect condition."

Studies are underway to see whether Lo Wu station could host the next roof garden. Jim said there are other places in Hong Kong suitable for roof gardens, such as the Kwun Tong MTR station and many schools.

"When I was a kid I didn't get to step on grass a lot. My goal is to let the next generation of Hong Kong children be able to step on grass."

Perennial peanut and firecracker vines will be planted on the Tai Po Market station roof garden.

It will take six months for the perennial peanut plant to grow into a 20-centimeter thick greensward with yellow flowers.

The traditional zinc roof used on railway platforms tends to absorb heat. The zinc will be replaced by sandwich panel roofing with polyurethane rigid foam to reduce heat.

Spot cooling systems like that at Mong Kok station will be installed on platforms by next March.