Buildings present a unique opportunity to mitigate climate change and also enhance sustainable development. According to a 2007 United Nations Environment Programme (UNEP) report, the buildings sector, globally, is responsible for 30-40 percent of worldwide energy consumption and up to 40 percent of all greenhouse gas (GHG) emissions. In Singapore, air-conditioning alone comprises 40-50 percent of our buildings' electricity consumption.
While the buildings sector holds the dubious honour of being the largest contributor to anthropogenic GHG emissions, the good news is that it also has the greatest capacity to reduce these emissions. Significantly, the Intergovernmental Panel on Climate Change (IPCC) has suggested that sizable reductions in emissions from the buildings sector can be made at zero cost or at relatively low levels of investment.
Singapore's first Zero Energy Building (ZEB). (Photo credit: Building & Construction Authority)
Plants may be green...
A concept initially developed in Europe, green roofs and rooftop gardens are becoming increasingly popular here due to their ability to reduce buildings' air-conditioning requirements, as well as filter out particulates, cool city air, and absorb large quantities of storm water. A local study conducted jointly by the National University of Singapore and the National Parks Board found that installing a rooftop garden reduced buildings' annual energy consumption by up to 14.5 percent. A study in Greece found that a layer of plants could shield off as much as 87 percent of solar radiation.
When thinking of "green" buildings, one conjures images of verdant structures that stand in stark contrast with the harsh concrete surfaces of their less eco-friendly neighbours. Such buildings are literally green--their walls and rooftops converted into sky gardens and vertical gardens with lush foliage. Indeed, the growing global awareness of the environmental implications of urbanised lifestyles has been reflected in the greening of many city skylines.
Here in Singapore, we need to tap the potential of the ubiquitous grey concrete surfaces which form the bulk of our urban fabric to reduce carbon emissions and improve energy efficiencies.
...But not always green-friendly
However, while the aesthetic benefits of green roofs cannot be denied, it is not simply a matter of hauling up pots, soil and seeds. In the quest to make our buildings more environmentally-friendly, there is a need to look beyond actual greenery for practical solutions that match the particular circumstances of individual buildings. The benefits of roof and vertical gardens can be overshadowed by installation and maintenance costs.
Specialised membranes and drainage barriers must be purchased as part of the green roof infrastructure. The types of plants grown must be chosen carefully for their ability to withstand the environmental challenges inherent in the rooftop setting. In Singapore, most plants require considerable irrigation as well as fertilisers, pesticides and pruning. The costs of maintaining this greenery are exacerbated by Singapore's annual dry spells during the late northeast monsoon season in February and early March. The reality is that putting live foliage on the rooftops of older buildings is often difficult and prohibitively expensive.
Green building schemes in Singapore
To meet sustainability goals, the Building and Construction Authority (BCA) set a target whereby at least 80 percent of buildings here will be green by 2030. A number of policies and measures, such as the Green Mark and Energy Smart building labelling schemes, have been devised to this end.
Given that Singapore is already very highly-urbanised, most of the greening will in fact have to occur through retrofitting of existing buildings. Thus, perhaps we should focus on more practical solutions to improve the environmental performance of our buildings.
When non-green materials can be solutions
For instance, research conducted in Puerto Rico found that installing a passive rooftop cooling system comprised of corrugated aluminium sheets and polyurethane layers can reduce indoor cooling loads by as much as 79 percent. Similarly, a study conducted in Sri Lanka found that installing insulated roof slabs reduces the amount of energy required for air-conditioning.
In terms of energy conservation, these solutions have at least two advantages over the planting of bushes, shrubs, flowers, vines, etc. Firstly, they rely upon engineering expertise that is better established and widespread than the know-how required for green roofs. Secondly, they are typically easier to install and maintain, and require comparatively little capital investment. These factors make these options appealing to the managers and owners of existing buildings, especially commercial buildings and condominiums that are heavily air-conditioned.
Thus, the term "green buildings" should be taken to mean buildings that are environmentally sustainable and resource-efficient. They don't necessarily have to be crowned with live plants.
More eco effort needed for existing buildings
But this must not occur at the expense of taking decisive action now. The twin concerns of climate change and sustainable development provide an overwhelming impetus for carrying out relatively simple measures to "green" our buildings sooner rather than later.