Things are looking up in our quest for cooler, cleaner, greener cities … looking up to our rooftops, that is
Story: Geoff Wilson
How do begin your journey towards the creation of a home with a green roof or green walls? First, consult a structural engineer. This is the answer I provide to any homeowner who asks me how to go about building a green roof or green wall to enhance their home’s sustainability and aesthetic appeal.
This is not advice that originated with me, however. I was strongly advised that this was the vital first step by the many built-environment professionals I consulted overseas when I chose to specialise in writing about the subject. Obtaining sound advice about retrofits or new applications from a good structural engineer is like ensuring your house is built on solid foundations — it improves long term function and reduces maintenance for the next 20 to 50 years.
It should go without saying that green roofs and green walls must always be built to last because incorrectly built there is a risk it will fall down, possibly causing injury. The extra weight of building materials, plant-growing substrate and plant material on a rooftop can vary from a minimum of 60kg a square metre up to (or more than) 250kg a square metre. If deep-rooting shrubs and trees are desired on the rooftop of a house or apartment building, the weight allowance could be well above 250kg a square metre.
Few current buildings in Australia are designed for this. They have to be altered and reinforced if being retrofitted, or specially designed if new. In short, expect a green roof or green wall to be a disaster if you don’t consult an engineer because that’s been the experience world-wide so far and I’ve seen extremely sad pictures of expensive disasters caused by people who tried to save the expense of a structural engineer.
After the structural engineer has offered his or her advice, there are many other factors to be considered and experts to consult. These include:
• Choice of plants suited to your city or your building’s microclimate. Rooftop or wall plants will generally face hotter, drier conditions as climate change effects become more apparent. Australian native species adapted to hotter, drier conditions will thus be favoured. So, a well-informed horticultural expert who knows green roofs and walls technology is vital. Do not expect current nursery plants to have long-term survival.
• Choice of “soil” or substrate to best grow native plants on roofs and walls. These days little or no natural soil is used on roofs or walls because of weight problems or problems related to the holding of water or nutrients. Instead, the substrate used is a special mix that best meets long-term maintenance challenges. Therefore, a substrate expert is essential to supply the best growing medium for the new native plants currently being developed for use on rooftops and walls.
• Choice of water supply. Most green roofs and walls will require a special water supply system in Australia to overcome the annual seasonal droughts and the tougher cyclical droughts that we must regard as being inevitable. A good water advisor will talk about rainwater harvesting, storage and use or discuss renovating a building to make use of greywater – either one or both options can be used for to assure water to rooftop or wall plants, without using the municipal supply. Or he or she might advocate air-moisture harvesting, perhaps in conjunction with a greywater polyhouse. Whatever option is adopted, a really competent water specialist is recommended.
• Choice of construction company (or a construction supervisor) best suited to your design and to your finances. Do not expect all construction experts to know much about green roofs and green walls as the industry education process is only just beginning. So, if you can find a construction company, or a construction supervisor, who knows green roof and green wall technology, then you may well favour them if the price is right. Be careful of construction people who will wish to charge you double on the basis that they know little and want to cover their possible cost increases (and learning experience).
• Choice of waterproofing and insulation. Be very wary of built-environment professionals who say that waterproofing for green roofs and walls is “too difficult” or “too expensive”. It is not, thanks to new technologies from North America and Europe. Extra insulation for a green roof is desirable to provide maximum benefits in energy saving, reduction of use of air conditioning or heating, plus great protection against external noise or electronic intrusion.
• Choice of problem identification if waterproofing breaks down. European and North American companies now have computer-based technology which can monitor for unwanted water entry in a rooftop and pin-point its site for quick repair. While not yet available in Australia, this is a kind of insurance that I believe is well worth the cost. If the water-leaking advice comes to your computer and tells you its site, you can make a quick temporary response and tell a professional leak fixer the exact location of the problem. That could save you big money in repairs or insurance costs.
• Choice of maintenance regime and long-term maintenance contract. In North America and Europe, maintenance contracts for five to 10 years have to be signed at the time a green roof or green wall is constructed. This is yet to come in Australia but it is a choice that homeowner green roofers or green wallers should well consider. A green roof or green wall will need maintenance over its 20 to 50 year lifespan and as greenery grows and dies or needs cleaning or renovating. Far better to try to have experts making regular inspections and adjustments rather than allowing a valuable asset to deteriorate.
• Choice of designer. Go for the best green roof/green wall designer available. This is an investment that will probably cost you less in the long run. By being more efficient and better informed the project will be less prone to error that causes long-term financial pain. The best designers will be those who not only give your home new visual pleasure through the design of a green roof or wall but who wisely mesh new technologies in sensible climate change responses (for example, in water saving, in fossil energy saving, in improved solar power use, in air pollution control and more home production of sensible fresh food grown on nutrients from clean urban organic matter).
• Choice of energy supply — especially photo-voltaic (solar) power. If you’re considering a green roof or green wall merely for a single use then you are overlooking the other benefits available to you. Multiple uses of green roofs and green walls means that, in Australia, they can be used to make solar units 20-25 per cent more efficient in collecting electrical energy (by cooling the photo-voltaic equipment), and their cooling effects can also greatly reduce the cost of air-conditioning in summer. The next step and one that is expected soon is an Australian-designed solar power generator that is five to 10 times more efficient than currently available equipment. Green roofs and green walls will still need to be close by, however, to ensure maximum energy-collecting efficiency.
• Choice of fresh food from the roof or walls of homes now that the technology has advanced to the stage of being able to be driven by recycling of clean organic matter. My belief is that an attractive green roof or green wall can be designed to incorporate effective food production. I know of three Australian designers are now going down this path with green walls — one in Sydney, one in Brisbane and another in Perth — and there are probably others involved in commendable ‘food design’ projects who are worth seeking out.
• Choice of insurer. Expect insurance companies to provide lower premium costs for homes with well-designed green roofs and green walls that save fossil fuel energy and are less costly to run.
• Choice of municipal council. For most people this is probably not a valid choice because a building or home site is already chosen but if a potential homeowner wishes to invest wisely in a green roof and green walls, then the best result will also depend on a council’s knowledge of green roofs and green walls. Some municipal governments have acted fast to come to grips with green roofs and green walls technology as they relate to climate changes, others have not. If your council offers limited scope, you could always consider forming a lobby group to press for change and the adoption of more sustainable building regulations and practices.
From the points enumerated here it is clear that planning a green roof or green wall demands some time and effort but a growing amount of expert help is now available from Australian built-environment professionals who are learning about the latest techniques, technologies, materials and plants.
For more information on green roofs and walls visit the Green Roofs Australia Inc. website (www.greenroofs.wordpress.com) or the Green Roofs for Healthy Cities website (www.greenroofs.org).
Geoff Wilson is the founder of Green Roofs Australia Inc. (GRA Inc) and a director of the company running GRA Inc’s peak international organisation, the World Green Roof Infrastructure Network (WGRIN), based in Toronto, Canada.
Green roof benefits
• Reduced storm water run-off.
• Offsetting of carbon emissions.
• Improved quality of air.
• Increased urban biodiversity.
• Habitat creation and preservation.
• Better insulated buildings.
• Increased energy efficiency.
• Enhanced noise dampening.
• Additional open space.
More beautiful urban centres.
Green roof initiative
An Australia-wide national program for green roof and green wall education sites has begun in Brisbane with the Bulimba Creek Catchment Co-ordinating Committee (B4C) agreeing to the construction of a special green roof and green wall education demonstration shed at its new nursery in Carindale, Brisbane.
A Rotary Club of Carindale project, the unique green roofed and green walled structure will be used by Green Roofs Australia Inc. (GRA Inc) for its regular, one-day Elementary Green Roof and Green Wall lecture program in Brisbane. GRA Inc will also use the facility to initiate weekend lectures on green roofs and walls for Brisbane’s domestic homes.
The unit is being designed by GRA Inc. President Sidonie Carpenter and is expected to be a model that other Australian cities can adopt for their green roof and wall educational programs in collaboration with GRA Inc. The demonstration building is scheduled for completion in 2009.