Some 35m above the ground, a garden is blooming literally and figuratively. This garden is on top of the new wing of the 1-Utama Shopping Centre in Petaling Jaya.
Occupying nearly 2,787sqm, the garden is planted with some 500 species of rare tropical and temperate plants, possibly making it the largest rooftop garden in South-East Asia, in terms of variety and number of plants.
The rooftop garden idea was incorporated into the expansion of the shopping mall back in 2000 and was nicknamed “The Secret Garden” as it was secretly developed. It has recently been opened to the public on weekends.
1-Utama director Datuk Teo Chiang Kok, an avid gardener, was responding to the challenge of greening the development of the sprawling 400ha Bandar Utama township.
“Having a green roof insulates and blocks heat from the roof, thereby decreasing the air-conditioning required to cool the building. (This) allows 1-Utama to conserve energy and be environmentally responsible,” says Teo.
He says plants in the garden absorb carbon dioxide through photosynthesis and that helps reduce the carbon footprint of 1-Utama.
The soil mix used for the garden’s flower bed – granulated horticultural carbon – is a planting medium derived from compacted and carbonised sawdust that puts to use wood waste that would otherwise be rotting in dumpsites and releasing carbon.
Botanist Dr Francis Ng, who developed the growing medium with a private company, says the garden comes close to being a botanical garden where there’s a research element.
“The horticultural carbon is being tested with different plants. The most amazing result is with rice that is grown in containers. It shows that the usual way (submerging rice plants) is not the only way to grow rice.
“The medium is close to what is known as burnt earth. The carbon-rich soil allows air circulation to the root, delivering moisture and air to the plant without drowning it. That’s the secret of tropical gardening,” he explains, adding that the medium’s light-weight nature makes it the ideal soil for a rooftop garden.
Unfortunately, the horticultural carbon is not commercially available yet although Ng is trying to encourage the manufacturer and 1-Utama to look into commercial production.
To water the garden, the company adopts the natural way – harvesting rainwater which is at the heart of the stormwater management system that commercial buildings are encouraged to implement.
(Although the Department of Irrigation and Drainage’s Stormwater Management Manual was introduced in 2001, it remains a guideline. Commercial building developers are not legally required to implement it in their projects.)
Rainwater is diverted from the roof and stored in specially built reservoirs in the basement in all Bandar Utama commercial buildings, namely the extended wing of 1-Utama Shopping Centre, the Centrepoint Neighbourhood Centre, the IBM-KPMG Plaza and the One World Hotel. The harvested water is used for flushing toilets, watering plants and also supplied to the cooling tower of the air-conditioning system.
“However, the rainwater collected is not sufficient to flush all the toilets. It only saves us 30% of the total water consumption in the new wing,” says Alfred Chong, landscape manager of Bandar Utama City Centre, the subsidiary of Bandar Utama Group which manages the commercial units.
As the idea of a rooftop garden was envisaged from the start, the company was able to consider issues such as weight from the soil and vegetation, drainage and waterproofing the roof. Chong says the garden layout was planned such that heavy trees are located on supporting columns as advised by the structural engineer.
Another sustainable building practice adopted by Bandar Utama City Centre is the chilled water storage system that it says is a home-grown technology.
The system utilises the idle capacity in the national grid during the night. By running the chillers at night, it shifts 30% of the energy load during day time to off-peak hours. This narrows the disparity of power demand between day and night, thus reducing the need to build more power plants.
The company’s pioneering effort closely follows the growing importance given to rooftop space by city authorities worldwide.
Last month, Toronto (in Canada) approved a bylaw that requires new residential units over six storeys, schools as well as commercial and industrial buildings to have up to 50% green roof coverage. Chicago (in the United States) offers incentives to builders who put green roofs on their buildings.
It has been estimated that if all the roofs in a major city were “greened,” urban temperatures could be reduced by as much as 7°C.
Originally, a green roof was one where vegetation partially or completely cover the roof surface over a water-proofing membrane.
But the term has since taken on an expanded meaning to include green technologies that are introduced on that space, like harvesting of rainwater and harnessing solar energy through a photovoltaic panel. High-rise dwellers have also turned to using their rooftops to grow their own food.