Since the 1960's green movement, green roofs have ‘re-emerged’ as a viable solution to address pressing environmental issues like increased storm water runoff, the urban heat island effect, deterioration of air and water quality, and loss of habitat and biodiversity facing urban centres. Increasingly becoming popular worldwide, green roofs are still not an area local builders are keen to take on. Despite the availability of materials and suitability of climate here, they are held back partly by concerns pertaining to costs. The objectives of this study are to highlight the economic benefits of green roofs that can offset the initial costs; to examine the initial cost implications of having a green roof as compared to a conventional flat roof; to compute and compare the life cycle costs of roof gardens and average flat roofs; and to incorporate economic benefits by incorporating energy costs into life cycle costs. It is observed that life cycle costs of extensive green roofs with or without consideration for energy costs, are lower than that of exposed flat roofs, despite its higher initial costs. However, for accessible rooftops, even life cycle (energy) costs of intensive system are not less than the normal build-up flat roof.
The New Concept Plan 2001's vision calls for an even greener Singapore city. This blueprint is designed to turn Singapore into a thriving world class and very green city in the next 50 years [1]. One key aspect of this greening process is the use of more aesthetically pleasing plantings with trees, shrubs and grass in our urban environment.
With a current population of 4 million and a projected population of 5.5 million in 40–50 years time, all within a tiny island state of , the trend would inevitably move towards higher density housing exploiting almost every inch of land available. However, to maintain a pleasant living environment, the balance between vegetation and concrete built-up areas cannot be overlooked. With the fundamental layout of cities unlikely to change for some years to come, planners face the challenge of finding other means of increasing and enhancing the amount of greenery in urban areas.
One promising option for dense urban settings is the greening of buildings [2]. Roof gardens, though not a new concept, increase the percentage of greenery in urban built-up area and bring back the vanishing urban green space. Sprucing up the originally under-utilized portion of the buildings, they can ‘create a new network of vegetation linking roofs’ and increase the ratio of greenery to population. To a certain extent, roof gardens do contribute to the National Parks Board (NParks) target to develop of parkland per 1000 population.
Roof gardens, more commonly known as green roofs in European countries, are gaining foothold in North America while widely popular and established in European countries especially Germany, France, Austria, Norway, and Switzerland. A large amount of research has also been undertaken in an attempt to improve the performance of green roofs.
By comparison, the acquisition of green roofs technology into current design and construction practice through research and application to local context in Singapore is still in its infancy phase, with a considerable gap compared to our European counterparts. Nevertheless, the extensive research conducted in Europe, do provide us with significant insights of green roof technology commonly adopted there.
Many designs of plantings on rooftops are tried and tested in Germany but this does not mean that they can be totally adopted and adapted to the local context. One obvious reason is the difference in climatic conditions. Interestingly, German professor Manfred Koehler who has studied urban ecology for 20 years, commented that Singapore, unlike Germany, is not subject to seasonal changes, the weather conditions are ideal for plant growth and not much re-planting is required [3].
One key economic benefit as highlighted by German professor Manfred Koehler is that ‘green surfaces are less expensive than tiled roofs in the long run because they last longer’. Other than this attractive economic benefit, NParks is aware of the many other benefits (environmental, social, aesthetic and economic aspects) roof gardens have brought and thus, hopes to motivate the developers and builders to landscape Singapore's skyline [3]. Many initiatives have been undertaken to bring roof gardens to the awareness of developers and builders. The Garden City Awards, for instance, is one of NParks’ effort to recognize the hard work put in by developers, landscape architects and property-managing agents in making Singapore a garden city. These awards also try to encourage developers in greening the building development.
Despite the growing interest in green roofing and the fact that Singapore does have all the materials required for green roofs, many developers are often held back from including rooftop gardens in the design brief mainly by concerns like high initial costs and structural loading capacity [3].
The objectives of this study are as follows:
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to examine the initial cost implications of having a green roof as compared to a conventional flat roof,
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to compute and compare the life cycle costs of roof gardens and average flat roofs,
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to incorporate economic benefits by incorporating energy costs into life cycle costs.
