The incentives for green roofs and how the disincentives can be surmounted
NINA JAMES from the New South Wales executive committee for Green Roofs Australasia discusses the incentives for green roofs and how the disincentives can be surmounted.
Considering our national parliament house, which was constructed more than 20 years ago, boasts an enormous green roof, it seems curious that green roofs are not more commonplace in our cities. Parliament House’s green roof was not created for its potential environmental benefits; rather, the intent was to preserve the profile of the hill on which it was built.
There are tales of metaphors imbued in the architecture to afford the populace the opportunity to walk above parliament, as government serves the people. Either way, the green roof is providing a landscape setting for our most important political building, and is the poster child for green roofs in Australia.
The Australian green roof market is somewhat behind that of our northern hemisphere cousins. There are many reasons for this delayed take-up, such as:
- a lack of policy
- translation of a northern hemisphere product into an Australian climate, and
- little local research to support the claims of benefits undeniably.
GREEN ROOFS’ PRACTICAL BENEFITS
The proposed benefits of green roofs are impressive and span a broad spectrum of contemporary city planning challenges. To list a few: green roofs are capable of capturing, storing and treating stormwater; contributing to holistic watershed management; and improving water quality in a city.
By replacing the standard application waterproof membrane with an extensive (< 300 millimetre growing medium) green roof, it is possible to significantly improve the thermal performance of a building. This can be illustrated in reduced heat loads and energy consumption related to air-conditioning.
In addition to building performance, a green roof can reduce reflective heat, which contributes to urban heat island effect. By increasing green cover on a roof, it is possible to reduce the temperature at street level. The greenery absorbs the heat, transforming it by photosynthesis into energy for growth. Heat reduction is also increased by evapotranspiration on the roof.
BRINGING BIODIVERSITY BACK
There is also evidence that green roofs can assist with bringing biodiversity back into the city. We know that fauna habitat is detailed in its structure, which makes it difficult to synthesise. However, there are now many green roof case studies where colonies of local fauna have set up camp on the roof of a city building.
At the Green Roofs Australasia Conference in 2010, the researchers at the Adelaide Zoo reported that their green roof was home to several species of lizards, spiders and insects. This story is typical of green roofs in city environs. In fact, the Vancouver Convention Centre’s six-acre wild flower green roof by PWL Partnership boasts a healthy bee colony, as well as a surprise bunny resident.
Visually, green roofs offer a beautiful alternative to the standard waterproof membrane. They offer an opportunity to weave nature back into the city, which demonstrates seasonal change, deep in the concrete jungle.
OVERCOMING GREEN ROOF IMPLEMENTATION INHIBITORS
Given these impressive achievable benefits, it is perplexing to recognise the limited application in our CBDs, but perhaps this is not so surprising when several key factors are compared to other more successful cities.
Despite Parliament House, the green roofs industry is somewhat juvenile in Australia. We are still working out the appropriate local plant selections and are attempting to calculate exact improvements in building performance locally.
Many of the inhibitors to the large-scale employment of green roofs relate back to lack of information and awareness. One inhibitor, which is widely discussed, is risk aversion to potential perforations to waterproof membranes. The membrane is clearly critical in maintaining building health and should be vehemently protected. However, sophisticated leak detection systems that can locate early signals of leakage now exist for green roof applications.
The critical element here is certification and the tanking of the waterproof membrane; and this comes down to the contractor and foreman being appropriately trained. Another deterrent is the assumed increase in cost to install and maintain a green roof.
Depending on the scale of the green roof (intensive >300-millimetre, and extensive <300-millimetre), the roof may require additional structural support. For an extensive green roof, very little additional structure is required. Replacement of waterproof membranes is a costly investment and studies have shown that an extensive green roof can extend the life of the waterproof membrane by 20 years, doubling its lifespan.
A study out of the National University of Singapore concluded that an extensive green roof cost approximately 2 percent more over a 40-year lifespan than a standard waterproof membrane. The challenge here is to somehow compensate the builder/developer for what will ultimately become a building management benefit.
This introduces the issue and importance of policy in stimulating the local green roof market. Impressively, local governments are taking the lead in Australia and attempting to provide market stimulation.
The City of Sydney recently recruited a green roof project officer and an independent technical advisory panel to assist in developing progressive green roof policy. Policy instruments, such as incentives and subsidies, and command and control measures, have successfully been employed elsewhere to support the development of a green roof industry.
At a national level, pollution reduction, biodiversity, clean water and air policies set targets and standards for our cities to achieve. These are then interpreted at a state and local government level. Planners often lament the conflict and incongruence in local and state government planning. The lack of alliance makes command and control measures difficult to enforce.
At a local level, however, incentives such as reduced approval time, potential funding in partnerships, increased offset densities and reduced amenity rates could assist in promoting the industry. Perhaps by diffusing the initial cost increase, installing leak detection software and providing information to the construction industry, our cities could surpass our northern hemisphere cousins in the race to green the globe’s CBDs.
Nina James is the open space and recreation, and campus portfolio manager for CLOUSTON Associates landscape architects. James is currently conducting independent research into this topic area as a part of her masters program and wrote the article on behalf of Green Roofs Australasia.