Energy efficient buildings: green or grey-green, by Augustin Boey

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 is responsible for 30 to 40 per cent of worldwide energy consumption and up to 40 per cent of all greenhouse gas (GHG) emissions.  In Singapore, air-conditioning alone comprises 40 to 50 per cent 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.

A concept initially developed in Europe, green roofs and rooftop gardens are becoming increasingly popular here due to their ability to reduce air-conditioning requirements. They also 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 can reduce a building’s annual energy consumption by up to 14.5 per cent.  A study in Greece found that a layer of plants could deflect as much as 87 per cent of solar radiation.

The term “green buildings” 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 is 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.

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, we need to look beyond actual greenery for practical solutions that match the particular circumstances of each building.  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 from May to July. The reality is that putting live foliage on the rooftops of older buildings is often difficult and prohibitively expensive.

To meet sustainability goals, the Building and Construction Authority (BCA) set a target whereby at least 80 per cent 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.

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 per cent. 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 more 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, particularly 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.

A number of positive steps have been taken to boost Singapore’s urban “greening”. Most significantly, BCA has mandated that new and existing buildings undergoing major retrofitting since April 2008 must attain a minimum level of environmental sustainability equivalent to the Green Mark Certified level. While such measures will increase the number of green buildings, more effort is needed to make the existing building stock more energy efficient. Specifically, there is a real need for more local studies which compare the energy and cost savings of rooftop gardens and “grey” solutions.

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.

The writer is an Energy Analyst with the Energy and the Environment Division at ESI. Please forward feedback or requests to re-use all or part or the article, or to use figures contained within it, to

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