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November/December 2005

The next profit frontier for green roof companies is…

By Geoff Wilson, President of the Urban Agriculture Network – Western Pacific, and Convenor of Green Roofs for Healthy Australian Cities

All Photos Courtesy Geoff Wilson

Singapore has a new business opportunity – food production from its residential and commercial rooftops. It is an opportunity likely to open up to every city in the world.

Who better to embrace the opportunity as it spreads globally than the green roof companies already operating strongly in 16 countries?

A survey of the food-from-the-roof opportunity in Singapore, a thriving Asian city-state with miniscule farmland resources, has shown it may be able to devote up to 1,000 hectares of its urban rooftops to fresh vegetable production now mostly imported (at a considerable fossil fuel energy cost).

The Singapore Skyline has the potential to be green

Singapore is an island on which only about 1,500 hectares of farm land remains, most of Singapore Island being taken up with urban apartment blocks, commercial buildings, industrial areas, plus parks and nature reserves. This picture shows the commercial buildings, but extensive dormitory suburbs of high rise housing can be seen in the background.
It is the latter buildings, with flat roofs and extensive balconies, that "sky farm" bridges for growing food have been recommended.

When that happens it will influence myriad cities elsewhere.  Add to this rooftop opportunity the considerable food production potential in Singapore of:

• “Vertical farming” on the sun-facing walls of buildings;
• “Sky farms” on bridges between buildings;
• Intensive aquaculture in basements and at ground level.

This begins to outline a bold new opportunity for the global green roof industry currently developing strongly (and very reasonably) along non-food lines.  For what Singapore has in prospect today in food from the roof, the rest of the world will be offered tomorrow.

Left: The front facade of the Raffles City complex of three hotels and a shopping centre. No green roof development is visible from the street - but look down from the 40th floor....Right:  Two green roof projects are seen from the Swisshotel The Stamford. The first, in the foreground above the main Raffles City entrance, is a flower and garnishing "farm" for the complex. Just visible in the background is a smaller hotel with a rooftop garden, seen below.

Singapore Rooftop Garden Photo by Geoff Wilson

This zoom-in from the 40th floor of the 70-floor Swisshotel The Stamford shows a rooftop garden on a small hotel in Singapore. It is becoming much more popular -- and likely to be meshed with the growing movement in Singapore for rooftop food as well as recreation. Intensive fish farming on rooftops or at ground level can be the drive of aquaponics - in which fish wastes become the plant food for vegetables, food and flowers.

Major keys to this opportunity lie in food production technologies still developing, such as hydroponics, aeroponics and aquaponics – all of which better utilise fresh water.

Technology spin-offs from hydroponics and aquaculture are now expected to make Singapore, and my home town of Brisbane, in Australia, the two most likely world leaders in:

• Ground-level production of urban fin fish, crustaceans and mollusks in specially-designed containers, raceways or floating tanks using roof water runoff;
• Rooftop production of fresh vegetables, flowers and fruit from the wastes of such aquaculture – in a system named aquaponics;
• Tourism and education focused on the two technologies.

I predict that contributions in these fields in the two southern hemisphere cities will become as important as the admirable leadership in green roof development that Toronto, Canada, is now well showing in such things as building insulation, better handling of roof water runoff and aesthetics.

Both green roof streams are new business opportunities well worth grasping as climate change factors require the urgent attention of all of us – even if it’s on the principle of doing something “just in case.”

Let’s look at what is in prospect in Singapore to see how the future of our own cities on most parts of the planet can be glimpsed as if in a crystal ball.

A survey by Ngee Ann Polytechnic students supervised by their hydroponics lecturer Gregory Chow, found that four suburban areas of northern Singapore -- about one tenth of the total built environment -- had about 212 hectares of apartment and commercial rooftops to grow fresh vegetables, using inorganic hydroponics.

Extrapolation of this across the whole of Singapore reveals that that around 1,000 hectares of rooftop space could be available (relatively easily) for urban food production in Singapore.

Gregory Chow calculated that about 39,000 tonnes of vegetables a year could be produced from the 212 hectares he and his students studied. If these vegetables were sold for around $2/kg – the value of produce would be around S$40 million a year - approximately U.S. $ 23.5 million a year.

Given that the Singapore Government’s objective is to displace around 20% of the annual consumption of 380,000 tonnes of fresh vegetables consumed each year with local production (currently at only 5% pa of the total), this Ngee Ann Polytechnic study is significant justification for more serious analysis of rooftop production of fresh vegetables across the whole of Singapore.

It is reduction of so-called “food miles” writ large!

Gregory Chow has demonstrated already, what can be done in rooftop farming with his award-winning project on the atrium of the 800-bed Changi General Hospital, below.

The hydroponic farm on the atrium of the 800-bed Changi General Hospital in Singapore. The bare concrete of the atrium roof was a problem in that it diverted sunlight into nearby wards - to cause objectionable glare and heating. The rooftop hydroponics, growing cherry tomatoes and herbs, solved the problem and created a rooftop farm that now supplies patients with healthy fresh food. Another Singapore hospital is about to go even further in food from the roof.

Swing-out vertical gardens?

While this picture shows the traditional idea in Asia of family washing being swung out on poles, there's also potential for swing-out wall gardens from balconies on sunlit walls. I have a friend who is designing such a unit using patented oval-pipe technology and clip-together units. A vertical vegetable patch is the objective - linking with rooftop aquaponics.

The Ngee Ann findings and the Changi Hospital example highlight the great need for a similar economic study of the potential of another Singaporean innovation – the “sky farm” concept, which would blend in well with both the food-producing potential of Singapore’s rooftop spaces, plus the potential of “vertical farming” down the sunlit faces of apartment buildings.

Professor Lee Sing Kong, Dean, Graduate Programmes and Research, National Institute of Education, of Singapore’s Nanyang Technological University, has been advocating “sky farms” that use the aeroponic technology so well pioneered by Singapore’s AeroGreen Technology Pte Ltd., initiated by the Sime Derby company.

Aeroponics is where a hydroponic nutrient solution is sprayed onto plant roots dangling in light-proof boxes. It allows temperate-climate fresh vegetables to be produced economically in tropical and sub-tropical climates.

Professor Lee’s good idea is sunlit bridges between high-rise apartment buildings or even office towers. They could be retro-fitted as single or double units at first or second-floor levels, or part of a tier of vertical structures servicing the food (and organic waste management needs) of multiple stories.

Aeroponic vegetable production on the bridges would use nutrient solutions stored and cooled at ground level, then piped to light-proof boxes above. The “sky farm” bridges can thus be relatively light structures.

The significant saving with this system is the cost of farm and transport energy (mostly diesel fuel) and consequent air pollution with diesel particulates that are known to cause asthma, emphysema and even cancer – particularly in the very young and the elderly.

Tenants of the buildings would be able to harvest the temperate-climate or tropical-climate vegetables themselves, perhaps in co-operatives similar to the one already operating a rooftop hydroponic unit at Singapore’s Tanjong Pagar apartment complex, see below.

Hydroponics on the roof in Singapore; Photo by Geoff Wilson

A co-operative of high-rise apartment owners in Singapore operates these two rooftop hydroponic units to grow bok choy they share.  It is an idea that is expanding among other high-rise apartment owners.

It is my contention that Singapore could produce, most economically, at least a third of its future fresh vegetables from rooftops and “sky farms.” It may choose never to replace all imports, on either practical (e.g. potatoes) or cost grounds.

But in well utilising its rooftop resources it would provide the world with an important demonstration of how urban agriculture, designed into buildings, could greatly enhance the food security of many cities in the tropics and sub-tropics – and provide stimulus for further food-from-the-roof technology to be developed in other climates.

Besides taking up the good ideas of their own citizens, Singaporeans also need to look closely at the new equipment from Australia that is being developed for sub-tropical and tropical hydroponics, aquaculture, aquaponics and vermiculture. This equipment is capable of being meshed into urban agriculture that:

1. Has urban organic wastes changed into organic plant nutrients or organic fish feed in basements and at ground levels.
2. Has the waste by-products (e.g. excess worms or insect larvae) being fed to fish, crustaceans or molluscs growing in tanks or containers.
3. Has organic hydroponic growing of food plants on nearby rooftops (via piped nutrient solutions of fish wastes and worm liquors, refined via microbial action).
4. Has water being recycled to fish and crustacean tanks minus the plant food, and with superior aeration.

Hydroponics on the ground in Brisbane

Rykoff Hydroponic Farm in Brisbane, Australia

The photo at left shows a sub-tropical hydroponic farm growing bok choy in Brisbane, Australia using clip-together oval channel equipment under hail netting. It is the kind of food-from-the-roof technology likely to be adopted for Singapore rooftops - with the hail netting serving as a worker safety net, plus a barrier to rooftop debris flying away with wind gusts. An acre of this kind of hydroponics is more productive than six acres of good soil -- using less than a 10th of the water.

So Singapore's 1,000 hectares (2,500 acres) could be equivalent to more around 6.000 hectares (15,000 acres) of soil horticulture. What's more, the roof-grown fresh food is close to where it is needed above apartment blocks or restaurants -- thus saving substantial transport energy costs.

Singaporeans also need to look at the innovations in aquaponics now well confirmed in their great good sense in Canada and the United States – where rooftop growing of food is observable, but has yet to be given the technology thrust it needs.

Australian and North American companies involved in various forms of aquaponics via floating tanks or raceways will also have interesting options to offer Singapore, in both fresh-water and salt-water systems that combine the growing of fish (and other aquatic food animals), with the growing of food plants that can utilize their wastes, in rooftop farming and gardening, or on sunlit sides of buildings.

Australian hydroponic pipe system

The clip-together Australian oval pipe system that provides lightweight hydroponics for rooftops and balconies in Singapore.

If Singapore chooses to go down this exciting food technology road now being built for urban agriculture integrated into buildings, I believe it will be very pleasantly surprised at the number of people from around the world who will wish to visit it as techno-tourists for study tours, conferences, technical demonstrations and short-course education.

Sky fruit garden potential

Two Australian growers have proved that papayas in hydroponics, like this one, can be grown to production of fruit in little more than half the time of soil-grown "Trees." The hydroponically-grown fruit is claimed to be tastier. The tropical papaya is predicted to become a favoured fruit to be produced from rooftops under hail netting in Singapore, and could form a most attractive bank of foliage for rooftop restaurants that also picks and serve the ripe fruit chilled, juiced or in fruit salads.

In addition, Singapore could well position itself in an important response the world must now make to both the rising cost of oil energy through increasing demand, and the increasing likelihood of disruptions to oil energy supplies as a result of terrorism or regional shortages that may re-occur.

My home-city of Brisbane in the Australian state of Queensland has the same opportunity available to it, but is not as advanced technologically as Singapore – either in urban agriculture or urban aquaculture, nor in rooftop greening. The lush ground-level garden of Singapore, plus the city-state’s growing adoption of green roofs, has few equals elsewhere. Its municipal greenery is a delight to visitor and resident alike.

But the best urban agriculture response must include the adoption of food production systems that are less dependent on oil or coal for farming or transport energy.

It is a response in which organic hydroponics and aquaponics, driven by sensible waste recycling, will have a big future in urban-based agriculture on rooftops, sky-farms and use of vertical faces of city structures that can harvest the world’s cheapest energy source – sunlight.

I believe that the world’s rapidly-advancing green roof industry that has been cradled and nurtured in Europe, and now brought to a lusty infant form in North America, must look to Asia and Oceania for some new directions for profitable expansion of myriad services.

In its turn, the Southern hemisphere will be the great beneficiary of northern hemisphere green roof science and technology, and practice.

It will make for an interesting blend of collaborative projects and information exchanges between the 16 countries now forging an international alliance for broad spectrum green roof development – at a most opportune moment in the history of human endeavour.

The Chinese have a curse: “May you live in exciting times.” I regard it as a benediction when I look at all the possibilities for green roofs.

Geoff Wilson is President of the Urban Agriculture Network – Western Pacific, and a director of Nettworx Publishing Pty Ltd, based in Brisbane. Queensland, Australia.  Geoff has been a food and agriculture journalist and communicator since graduating from agricultural college in 1957.  He has written for most rural newspapers and magazines in Australia and New Zealand since then, and for a number in Asia, Europe and the United States.  He currently writes on urban agriculture, aquaculture, aquaponics, and hydroponics, particularly for “Aquaponics Journal” in the United States.

Green Roofs for Healthy Australian Cities logo, by Katherine Wilson

Geoff is Convenor of both the Aquaponics Association Australia, and the new Green Roofs for Healthy Australian Cities.  The North American Green Roofs for Healthy Cities organisation includes professionals in urban planning, architecture, built environment academia and development, suppliers of specialised materials and consultancy, specialised builders and horticulturalists and professional and trade press servicing these groups. In Europe there are now national green roof organisations in Germany, Austria, Switzerland, Holland, United Kingdom, France, Italy, Spain, Hungary and Sweden.  Others are in Japan, Singapore and Mexico.

Green Roofs for Healthy Australian Cities is currently recruiting members.  Membership promotion events for this Australian entity will be one-day seminars on green roof technology and practice, in mid-2006.  It is hoped the seminars can be run in Brisbane, Sydney, Canberra and Melbourne over two weeks in June 2006.

1. To provide opportunities for members to learn about green roof science, technology, practice, economics and environmental and social benefits.
2. To promote Australian education in green roofs, particularly in university and TAFE college courses that provide skills for the green roof industry that can be expected to develop, and careers for the students of these courses.
3. To promote Australian research in sound green roof development.
4. To provide networking opportunities for Australians wishing to study green roofs in Australia and overseas.
5. To publicise the environmental advantages of green roofs.

Geoff Wilson can be contacted by email:, or phone +61 7 3411 4524.

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