Sod roofs used as insulation in Scandinavia and Iceland over a thousand years ago; Mud huts with grass roofs in Tanzania; Le Corbusier choosing rooftop greenery and a few years back; then New South Wales government architect Chris Johnson arguing the green roof case. Green roofs are not new but their modern development “probably began with The Greens of the 1970s and 1980s that had big influences on municipal governments in Germany and Austria,” says Geoff Wilson, president of the two-year-old Green Roofs for Healthy Australian Cities (GRHAC).
Germany is still the leader. Its projects feature on the International Green Roof Association’s mostly European, East Asian and North American database and its standard guidelines, published in the 1990s, are the oldest — and some of the few — international regulations on green roofs. Nevertheless, after the GRHAC’s first national conference, held in Brisbane in February and the formation of a committee, members are confident Australia is catching up within the fast-moving and increasingly global network.
“Cities in the US are reporting a 25 to 50 per cent increase in growth in green roof installations in 12 months,” Wilson says. In the current climate — changing as it is — we are going to be hearing more about these natural roofs as they grow and cool and add a calming visual beauty to the urban landscape.
The two main types of green roofs are:
• Intensive — recreational, “a horticultural place for people to enjoy,” Wilson says, with pathways, ponds, benches and alcoves.
• Extensive — low maintenance, with a thinner layer of greenery, suited to roofs with little load-bearing capacity, created for insulation and, says Wilson, “better handling of run-off water and to help reduce ambient temperature”.
Semi-intensive (or semi-extensive) roofs have differing weight and maintenance levels. Roof gardens mostly have plants in containers. Green roofs (and Atlanta-edited www.greenroofs.com insists on using one word) are vegetated roofs, with growing media. Herein lies their excitement and challenge. There is no one technology. Green roofs combine the “black arts” — the waterproofing; and the “green arts” — the “plant selection, substrate choice, plant establishment and maintenance,” Wilson says.
Wilson and landscape designer and horticulturalist, Sidonie Carpenter, identify the types of specialist who could be involved with a large-scale project. Carpenter recently returned from a study fellowship of Singapore and North America (supported by the likes of Multiplex Australia and Mirvac Australia). Urban planners, owners, regulators, building certifiers, architects, landscape architects, engineers — structural and hydrolytic, builders, waterproofing installers, plumbers, horticulturalists, composters, plant nurseries, plants breeders, planting labour and maintenance contractors might all be included.
Teamwork is essential. “Everyone has to be working on the same page,” he says, “in unison and understanding what is required.” Product choices depend on variables such as type of roof, new or retrofit, climate, budget, access and maintenance. Layering includes the most visible, the plants, through soil and sand, geotextile filtering fabric, drainage to waterproofing membrane, preferably root resistant. “You have to ensure the roof won’t collapse or leak,” says Wilson.
In Australia specifiers mainly have to look at each layer as a component part with a separate supplier and/or installer. There is the opportunity to take advantage of Australia's many hardy plant species from coastal and inland areas. Further to this the University of Queensland is researching sub-tropical species and the University of Melbourne, temperate plants suitable for green roofs. Wilson mentions Elmich drainage, substrate and waterproof membrane company and Fytogreen, which is the most quoted supplier of an integrated system and installation service and is listed as an eco and health preferable product on Ecospecifier. (The updated earth roofs book from David Baggs of Ecospecifier is Australian green roofs and earth covered buildings.)
Both Elmich and Fytogreen are international companies. The Fytogreen system is highlighted by a lightweight water retentive substrate called Hydrocell RG30, which replaces the traditional sand layer, and allows greenery to exist on thinner profiles. “The intensive green roof profile is 200 mm upwards and the extensive, 100 mm,” says sales and marketing manager Stuart Tyler. “Fytogreen has been used on 11,000m2 of intensive green roofs and roof gardens since 2004,” he says. Melbourne projects have covered 8,000m2 including Australand’s Freshwater Place, and Fytogreen is now introducing extensive roof projects, at concept stage.
Protection of the membrane during construction of other green roof components is critical. “If it gets damaged then you can imagine the cost of removing the installed green roof to repair the waterproofing,” Carpenter says. “A very good line of communication between all builders (and) subcontractors is required from day one.” This is especially important as installers and building managers may well change and “in the absence of a maintenance manual the wrong plants might be used to replace old stock and inappropriate irrigation regimes can be imposed,” warns GRHAC committee member, Ben Nicholson of Groof Consulting. “Effective ongoing maintenance is therefore crucial to the health, appearance and performance of the green roof.”
Nicholson believes green roof-specific regulations, product standards, standard assembly guidelines and inspection checks are needed to convince Australians to take up green roofs. It is early days yet. Australia is still far from stipulating, as in Tokyo, that green roofs over 1,000m2 are mandatory, or Basel, Switzerland, where every flat roof is to be green. “There’s still much to be done,” says Wilson, “but councils are already developing a better process to handle green roof and green wall development applications (vertical greenery is also catching on). It is up to the municipal government officers to judge the safety aspects and compliance with existing codes or standards.”
Brisbane City Council recently became the first city in the world to include both green roofs and urban agriculture e.g. food grown in an urban setting, in a climate change action plan. Brisbane is also offering cash incentives for developers implementing green roofs in their buildings. Widely agreed environmental, social/ psychological and economic benefits indicate that green roofs will be more than a passing fad. These include thermal insulation and reduced energy costs; noise reduction; recycling of water; reduced dust and smog pollution; natural habitat and food growth; variation in plant species (being careful to avoid potential fire hazards and choosing, for instance, succulents that a Berlin study found to be fire resistant); stormwater maintenance with reduced water run-off and flooding; a sense of place; and reductions in the urban heat island effect (difference between city temperatures and those of the surrounding countryside) particularly important as domestic violence and deaths increase in stifling night-times, studies in Brisbane and Tokyo respectively have shown.
Several of these factors would already gain credits in the Green Building Council of Australia’s (GBCA) Green Star rating systems, though both the GBCA and GRHAC realise more research is needed for green roof-specific measures. People’s ignorance of green roofs currently is a barrier and GRHAC members recognise the importance of education. They are considering adapting introductory courses from North America on green roof design and building as a start. Liberal MP Gary Hardgrave has even called for a national debate on green roofs (Parliament House has Australia’s biggest green roof). Green roof legal expert David Kelly plans to prepare a feasibility study into green roof carbon savings, both direct cost savings and reduced greenhouse gas emissions.
Green roofs cost at least 10 per cent extra (to install), Wilson says, but “international real estate professionals are getting 10-15 per cent extra valuation from buildings and easier renting because tenants like green roofs”. Overall, he believes green roof development here is permanent because, quite simply, “they are now bound up in the sensible responses to climate change problems likely to be ahead of urban communities”.
