Key Definition: Green Roof

04/12/2021

Green roof:

(Also referred to as living roofs; eco roofs; ecotecture; roofscapes.)

Their usage dates back to 10thC BC throughout Persia with particular reference to Babylon, as green roofs were used as a storm-water management system irrigating a stepped series of planters throughout the city creating a lush cool urban environment aka the Hanging Gardens of Babylon. Scandinavian ‘sod’ roof housing has been built since 1000AD to insulate dwellings during summer and winter. Throughout the 20thC there were progressive architects using vegetated roof-tops, however it was not until a green roof renaissance started in Germany during the 1980’s with R&D by FLL producing a definitive guideline for specification of green roofs. In 1986, Patrick Blanc pioneered his irrigated felt Verticle Garden (aka living wall) in Paris, which completed a technology capable of vegetating every building facade. The technology is now referred to as ‘Building Integrated Vegetation (BIV) systems.

Definition:

A green roof is a vegetated roofing system which is functionally integrated onto a roof area. Designs are site specific depending on climatic conditions; slope; access; structural capacity and intended usage. Standard components are a tested waterproofing membrane; root barrier; drainage outlets; drainage layer; geofabric; grow media; vegetation; irrigation; maintenance regime.

Green roofs are sometimes referred to as the fifth façade. There are three kinds of green roof: extensive; semi intensive & intensive, each type requiring particular engineering.

A simple way to differentiate the types is :- EXtensive is less / INtensive is more.

Types:

Extensive Green Roofs:

Shallow growing medium – 90 to 300mm.
Roof engineering similar to conventional standards.
Vegetation limited to shallow rooting plants.
Relatively economical.
Relatively easy to retrofit
Average saturated weight @ 150kg/sqm

Semi Intensive Green Roofs:

Grow medium depth – 300 – 500mm
Plant range; ground cover to small trees
Irrigation suggested
Root barrier suggested

Intensive Green Roofs:

Deep growing medium – 500mm or greater.
Greater saturated load..
Wide range of plantings possible.
Relatively expensive.
Greater benefits, insulation, water retention etc
Root barrier & Irrigation suggested
Leak detection system suggested
Higher biodiversity

Green roofs may appear as manicured lawns or natural plant communities. Extensive green roofs that use a thin layer of growing medium to support ground cover plants with short roots are generally designed with building performance in mind rather than aesthetic concerns. Sloping and curved extensive green roofs may be seen from ground level.

Intensive roofs can support quite substantial, highly visible vegetation, cascading over the sides of the building or as shrubs and trees rising above the roo?ine. These are commonly referred to as roof gardens. By creating a landscaped surface green roofs can radically change a building’s ‘roof line’.

Green roofs and external green walls (which can be small and incidental or large and dramatic) extend the scope for creating pleasant urban environments by introducing plants and greenery that are visually restful or refreshing. Proven therapeutic effects include increased productivity with improved concentration levels; improved psychological health and happiness.

BENEFITS:

Green roofs provide a multitude of benefits to the people who interact with them and the cities and regions in which they exist. Benefits are delivered across three spheres, environmental, economic and social, making green roofs a truly sustainable feature. In fact, it would be hard to argue that any other architectural element of a building can have such wide and profound benefits as a green roof does.

The benefits of a green roof range from a single user observing a roof to reducing the planet’s CO2 emissions through sequestration. The benefits described below have been dived up into Environmental, Economic and Social sections. However, as with true sustainability, many of these overlap. A further distinction is made if the benefit is private, that is mostly delivered to a signal person or organization, or public, those benefits derived by all. Many green roofs deliver both public and private benefits, making green roofs an equitable and egalitarian solution for our cities and homes.

Social Benefits

Physiological/mental health

Green roofs can improve a person’s mental and physiological function by allowing them to view ‘natural’ scenes and elements. Such experiences have been shown to relieve stress, improve productivity and reduce blood pressure.

Improved Biophilia “A human’s innate need to connect with Nature”

Exposure to nature or natural scenes, even for periods of as little as 3-4 minutes, has been shown to reduce symptoms of stress and restore cognitive function. Most city cores have a lack of either accessible or viewable green space, thus denying city-dwellers a means to escape from the demands of their daily lives or the opportunity for mental rejuvenation.  The inability to experience nature’s involuntary stress reliving power can place people at risk of poor productivity, anti-social behaviour or symptoms of mental illness. Green roofs supply an important resource of ‘natural environments’ in a landscape dominated by built structures. Due to the built form of many modern cites, green roofs might be the only option for introducing green space.

Green roofs can deliver many public and private physiological benefits. In the case of an office roof garden for example, it may provide a venue for relaxation, socialising or ‘time out’ for the employees of the building, improving staff wellbeing and productivity. The same roof however can also be viewed by an office worker in an adjacent building and they too can enjoy the mental respite by simply viewing the natural elements of a green roof.

The ability of green space to relive stress and improve physiological function has seen an increase in installation of green roofs in European and North American hospitals. In the redesign and redevelopment of the Royal Children’s hospital, Melbourne, the use of evidence-based design led to the installation of 360m2 green roof for use by patients, staff and visitors alike.

Increased Amenity and recreation opportunities

Many cities lack adequate open space. Green roofs provide an opportunity to increase the amount of useable space available for the pursuit of both passive and active recreational activities. Since they are composed of natural elements and replace underutilised space, green roofs can also improve the quality and attractiveness of building and its surrounding location.

The high population and employment density of cities has resulted in a many being composed of a practical yet bland built form. This functionality has come at the expense of amenity and recreational opportunities for the people who live and work within these areas. Green roofs can actively increase both of these components in our cities. The fact that many roof areas are comparable, if not greater in area (sloped roofs) then the foot print that their respective building occupies provides the potential for vast amenity and recreational opportunities.

Amenity

Green roofs provide natural colour, variation and stimulation to an exceptionally featureless component of a building- the roof. By using vegetation, green roofs can add an almost limitless amount of interest to a designated space. Amenity is derived from using the elements of vegetation which stimulate a person’s senses of touch smell and sight. Plants can be used which have different coloured or textured foliage, various growth habits or structures and variety of shaped, coloured and scented flowers. The seasonality of vegetation allows a green roof to seamlessly change from month to month.

Amenity however doses not have to be designed into a green roof. The very conversion of a roof from built elements to natural elements generates its own amenity. Studies have shown that people have a strong affinity for places and views which contain natural elements. Such views have also been shown to reduce feelings of stress and allow relaxation, improving overall wellbeing. The ability of green roofs to introduce ‘natural’ elements into our cities, intrinsically improves its amenity.

Recreation

Venues for people to participate in either active or passive recreation are vital to the function of a healthy community. Green roofs provide the basis to create new recreational opportunities on sites currently under-utilised. Many businesses are realising the benefit that creating an outdoor space where its employees or customers can socialise and relax. This is becoming common many restaurants and bars, with roof gardens a common incentive for attracting customers.

Other sites, such as residential apartment blocks, have seen the potential of green roofs to combine active recreation infrastructure such as pools and tennis courts in a natural and pleasing setting.  Some venues have opted for green roofs which allow the provision of recreational facilities but also utilise space, an example of this is the Docklands stadium in Melbourne, which has its playing surface located on top of an underground car park. Other gardens provide a venue for community groups to participate in recreation pursuits such as vegetable growing or gardening.

Food production

As the urban agriculture movement continues to grow, there is an increased desire to find suitable sites for food production in our cities and towns. Green roofs are vital in supporting this trend as they can supply new and non-toxic sites for the growth of edible plants.

Green roofs are becoming increasingly popular sites for food production. They provide an important element in the growing “urban agricultural phenomena”, which is developing in many regions. Green roofs generate food growing sites in a landscape where productive land is very difficult to obtain.They are advantageous to food production as they are composed of a constructed growing media, ensuring the potential for pollutants and toxic contamination is eliminated. Contaminated soil is an issue that currently hampers many urban agricultural projects which take place on reclaimed urban sites. The production of food in areas close to where people live, an objective of urban agriculture, also has the potential to reduce CO2 production from the transportation sector by reducing the distance food needs to travel before reaching market.

Noise reduction

Green roofs have been proven to be excellent and economical insulators for sound emissions. They can be employed to shield a building’s internal users from external noise pollution, or protect a surrounding location and its people from sound which may emitted from within a building. Such a function is important in protecting local amenity as well human health.

Noise generated within or around buildings can be significant and may vary from a nuisance to a serious health concern. Green roofs can be effective insulators, deflectors and absorbers of sound. This ability is derived from green roofs mass, composed of its growing media, vegetation and the layers of air which are trapped within its structure. Green roofs can be employed to contain the emission of noise generated from the operations of a buildings, such as industrial processes.

In the redevelopment of the Union Building at the University of Tasmania, Sandy Bay, Australia,  the sound insulation benefits of a green roof were one of the main drivers for its installation. The former building regularly staged live music concerts, which the new building intended to continue. However, being in a residential area, these concerts regularly resulted in high noise levels for local residents. The new building with green roof was able to deliver reductions in sound transmission of up to 19 dBA, making the concerts almost inaudible to surrounding residents.

Likewise green roofs can insulate users of a building from sound which is generated in the outside environment. Green roofs have now become an effective and common sound mitigation measure for buildings under the flight paths at the Frankfurt International Airport, Zurich-Kloten International Airport and Schiphol International Airport.

Environmental Benefits:

Increased biodiversity

By creating ‘new’ green spaces within our cities and towns, green roofs can provide opportunities for increased biodiversity. Through appropriate design and plant selection they may help conserve a threaten species or provide an important breeding or feeding location for a species of bird or insect.

Urbanisation has resulted in the loss of substantial amounts of biodiversity. This has resulted in the local or total extinction of certain plant, animal and insect species as well as the loss of ecological function. Biodiversity loss can be intensified by a predisposition for cities to our in ecologically rich locations. Due to the highly built structure of cities it can be very difficult reintroduce any more then discrete of components of an ecosystem, such as trees, at ground level. This is because available space is very limited and a high level of competition exists between a city’s various stakeholders for its usage. Green roofs on the other hand, provide the opportunity to create vegetated areas which contain multiple ecosystem components on currently underutilised and neglected space.

Due to the novel structure of a green roof, their shallow substrate and varied water availability, they are not able to recreate the exact ecosystem which their respective building may have replaced. However, they can create important ecological stepping stones for plants and animals. These green ‘refuges’ can help connect plants and animals between more substantial or remnant ecosystems and in the process facilitate ecosystem functions such feeding and reproduction. This green roof ability has been shown to be very important for urban populations of birds and insect.

Green roofs can also play an import part in helping to conserve species that may be vulnerable in the surrounding urban landscape. With appropriate design, plant selection and installation of habitat components, such as hollow logs, green roofs can support a large variety of plant and animal species. Further, the fact that many green roofs may be inaccessible to the general public can benefit conservation objectives.

Thermal regulation

With the combination of a growing media and vegetation, green roofs can provide substantial thermal mass to a building. This helps reduce fluctuations in temperature, making climate regulating equipment such as air-conditioners more efficient.

By replacing a poorly insulated and highly temperature conductive roof surface with a green roof, many positive thermal outcomes can be achieved. The mass of a green roof, its transpiring vegetation, layers of trapped air, reflectivity properties (albedo) and a water holding substrate all help to either reduced the amount of heat energy adsorbed by a building or the amount lost. Overall, this delivers a building with better thermal performance, reducing the both level of temperature regulating required (e.g. air conditioners) and improving the efficiency at which they run through reduced ‘leakage’. Green roofs are extremely effective at reducing a building’s cooling requirements. This is due to their ability to not only decrease the amount of energy adsorbed, but also transform heat energy through the process of evapotranspiration of the vegetation and evaporation from the growing media.

With a major proportion of a buildings energy requirements dedicated to heating or cooling a building, improvements in thermal regulation can produce significant energy savings. Since the vast majority of Australia’s overall electricity is generated from fossil fuels, green roofs can be an important tool in reducing the nations C02 emissions.

Carbon sequestration

Plants and growing media can both sequester and store carbon. By increasing the area which is covered with these components, green roofs too can be responsible for removing carbon form the atmosphere.

Carbon Sequestration is the process of taking Carbon dioxide (CO2) out of the atmosphere and storing it for a period of time. By supporting both vegetation growth and a ‘living’ growing media, green roofs have the ability to sequester carbon.  The amount of carbon which is ‘taken up’ by a green roof and the period for which it is held by the roof is dependent on many factors. The section below gives some basic information on the main factors which influence carbon sequestration on a green roof. It’s important to remember when talking about carbon sequestration that carbon is not just held in the visible biomass of a plant, the branches and leaves, but also in the soil. Soil carbon includes living components, e.g.  Soil organisms, fungus, bacteria and plant roots, as well components that are ‘dead’, such as logs, leaf litter and deceased organisms.

Plant species

 The amount of carbon a plant can take up is highly dependent on the species, its growth habitat, life cycle and interactions with other components in the ecosystem. For example, green roofs that support larger species such as trees and shrubs have the potential to sequester and store more carbon then one composed entirely of low growing ground plants, such as sedums. The function of a plant is also affected by its surrounding environmental conditions. Plants sensitive to drought grown on a green roof more likely to dry out may be less effective in taking up carbon then those species which are more drought tolerant.

Growing media depth

The growing media plays an important role in the carbon cycle. A major limiting factor of green roof substrates is their depth. Depth may play the following roles in an influencing a green roofs sequestration abilities.

Temperature

Shallow profiles can increase the temperature of the growing media. This in turn can ‘speed up’ the rate at which things decompose. The faster decomposition occurs, the more carbon is lost to the atmosphere.

Water content

While the amount of water available in the growing media is very important for plant survival, it is also influential on the processes that take place within the soil (or growing media) profile. The bacteria, fungi and organisms which are involved in the carbon cycle all have optimum conditions at which they operate. Extremes on either side will alter the capability of the green roof to act as a carbon sink.

Available volume

The depth of a green roof’s growing media obviously affects the total volume of the media’s profile. The relative volume of the profile will affect its ability to hold water, support root growth and harbour soil organisms and micro flora—all of which influence a green roof’s capabilities as a carbon sink.

Storm water treatment and management

One of the most influential benefits of a green roof is their ability to reduce both the volume and intensity at which rain water is delivered to the stormwater network. This alleviates environmental degradation of creeks and streams while decreasing the likelihood of flash flooding, which damages infrastructure and homes. Water originating from a green roof is also likely to be less polluted, providing further environmental and human health benefits.

Urbanized areas are characterised by a large percentage of impervious land. When this impervious surface is connected to drainage infrastructure such as storm water drains it can have serious consequence for the streams and rivers which receive this water, as well as risking lives and property. Green roofs actively manage the volume and duration which storm water is delivered to drains, while also filtering out many undesirable components.

In a natural forest ecosystem for example, only about 15% of water ends up as runoff after a rain event. The rest is either intercepted by vegetation, percolated to underground water or evaporated back into the atmosphere. The story in highly impervious areas, that is land surface covered with concrete and tiles, is quite different. In such environments water is neither intercepted nor allowed to soak into the soil. Instead, it accumulates quickly on impervious surfaces and is delivered rapidly to creeks and streams. In fact over 90% of water in urban areas ends up as run off. This intense inflow of water physically damages water ways by increasing erosion and dramatically alters the ecological conditions within them. In the process of reaching streams, urban storm water collects various pollutants such as toxic chemicals from cars and industry, as well as fertilizers and animal faeces. These are delivered directly to the waterway without filtration, damaging the complex ecosystem.

Green roofs reduce both the amount of runoff derived from a roof and the intensity at which it is delivered to the storm water network. This is achieved through a variety of means. Firstly, vegetation intercepts rainfall before it makes contact with the ground. Some water is ‘captured’ by the plants and remains on the leaves and stems while other droplets are deflected. Once in the groundwater, the rainwater must percolate through the media before entering the drainage network, this is as opposed to the impervious surfaces where water quickly enters the drainage system straight away. While contained in the soil profile, water may also been taken up by transpiring plants, further reducing the amount of water that enters the drainage system. This also dramatically slows stormwater drainage into natural waterways. A reduction in volume intensity not only improves the health of the water ways but also protects infrastructure and people by reducing the chance of flooding.

Green roofs also act as storm water filters. While contained in the growing media the quality of water can be improved through various both biotic and abiotic means. This includes filtration of particulate matter, reducing total suspended solids (TSS), as well as the adsorption and break down of chemical compounds such as nitrogen and phosphorus. The vegetation on a green roof also aides the removal excess nutrients or unwanted chemicals.

Urban heat Island

The high density of heat-absorbing materials in our cities, such as concrete, has led to these areas experiencing higher temperature then the surrounding countryside. This is known as the Urban Heat Island (UHI) effect. By reducing the area of heat-absorbing materials which are exposed to the sun and cooling their surrounding environment by the process of evaporation, green roofs can reduce the impact of the UHI effect.

A trend notice in the early 19th century and now well documented is the Urban Heat Island (UHI) effect. The UHI is the occurrence of warmer temperatures, especially those recorded overnight, in cities, when compared to the surrounding country side. The main cause of the UHI effect is the high proportion of impervious surfaces and predominance of heat absorbing materials such as concrete, asphalt and steel. During the day, these materials absorbed energy from the sun, As the day cools and becomes night, they radiate this energy back out as heat, warming the air temperature of the city. The multiple surfaces of a building, reduced vegetation-which limits evapotranspiration cooling and the waste heat energy generated from engines and buildings also contributes to the observed warming.  The UHI effect can have many negative impacts on both the environment and those people which live within the cities. This includes increased health risk form amplified temperatures, changes in the local climate (e.g. rainfall, frost days) and inflated energy requirements and hence greater carbon emissions.

Green roofs can be very effective tools in mitigating the UHI effect. They reduce the area of exposed heat absorbing surface (e.g. concrete), they cool the surrounding environment through evapotranspiration and they improve a building’s thermal efficiencies- reducing the requirements for cooling. With evapotranspiration predominantly mitigating the UHI the type of plants used, and more importantly the amount of water available in the growing media, will have a significant impact on the effectiveness of green roofs in cooling a cities temperature.

Single green roofs on their own are unable to have great impact on the UHI, however multiple roofs of the area on a city can. Roof spaces provide a substantial amount of surface area within a city, for example 19% of New York surface area is composed by roof surfaces. If this space were harnessed for green roofs, this would have a measurably significant impact on the UHI effect.

Air quality

Emissions from industry and vehicle transportation generate chemical airborne pollutants and particulate matter. These toxic substances are responsible for serious health problems, as well as damaging ecosystems and the built environment. Through the presence of vegetation, green roofs are able to trap particles and take up gases, removing them from our atmosphere and waterways.

Many large cities are now beset by numerous days of poor air quality. Poor air quality is attributed to both chemical compounds and particulate matter concentrated in the atmosphere above a city.  Emissions from industry and road-based transport contribute significantly to the attributes of poor air quality.

Reduced air quality events present many serious health concerns for those exposed. The elderly and young children are most vulnerable to its ill effects such as respiratory diseases. Increased particulate matter within the air can exacerbate the green house effect, raising temperature in surrounding areas.

The vegetation of green roofs has been shown to be able to actively ameliorate negative air quality conditions. Plants are able to trap air born particles, heavy metals and volatile organic compounds, hence removing them from the air. The removal of these compounds by plants also reduces the volume at which these pollutants are deposited onto urban surfaces and subsequently washed into waterways by storm water flows.

Habitat

Green roofs can provide the important living and non-living components needed for the survival of a plant or animal. This involves supplying resources for feeding, reproduction and succession. By fulfilling these demands a green roof can become habitat to a variety of plant and animal species.

Green roofs can create habitat in an environment which had previously been inhospitable to colonization of plant and animal species. A green roof provides three functions which allow the creation of a habitat. They provide of a physical surface and elements for which plants, animals and non-living components can exists, including water and nutrients. They support biotic components such as vegetation and other organisms, which may provide food, protection or breeding requirements. They provide the structure for which an organism needs to complete its life cycle including the abiotic components such as rocks, hollows and pools. Examples of green roof habitat vary from the visually obvious vegetated roofs which support birds and insects, to examples in the U.K which are composed almost entirely of gravel and are homes to specific invertebrates.

Climate change adaptation

Climate change is altering, and will continue to alter the physical environment in which we live. To transition to, and live with these changes, we will need to modify our current infrastructure and lifestyles. By managing the flow of stormwater, increasing a buildings thermal efficiency and reducing energy needs, green roofs can be an integral component in adapting our buildings and cities to the projections of climate change.

The IPCC predicates that climate change will result in altered climatic conditions and cycles. Models by the CSIRO show that in Australia climate change will result in increases temperatures, rise in the frequency and severity of heat wave conditions and deliver more server storms and high intensity rain events. Green roofs can play an important role in helping people, buildings and entire cities to adapt to these new conditions.

Rainfall

While the CSIRO models show that many parts of Australia will experience reduced annual rainfall as a result of climate change, the frequency of intense rainfall episodes may increase. In cities, which are characterised by a high percentage of impervious surfaces, this produces both instantaneous and intense run off. Many cities current storm water infrastructure will be inadequate to handle such volumes and fail, resulting in flash flooding. Green roofs can reduce the amount (volume) of water delivered to the storm water system and increase the time frame over which it is delivered, substantially diminishing the potential for flooding. This effect can be further enhanced by the tendency for green roofs to harvest their own water.

Temperature

With an increase in temperatures and an increase occurrence of high temperature days, incorporating elements which will maintain a buildings comfort level, but reduce its demand on resources is becoming an imperative. Green roofs meet this objective by suppling an important means of passive temperature regulation. In summer time green roofs reduce a buildings temperature through their thermal mass, decreasing the available building area exposed to the sun and by converting heat via evopotranspiration. Evapotranspiration is a process whereby heat energy is used to evaporating water from a plants leaves cooling the surrounding environment. Evapo-transpiration works the same way sweat does on your body.

Cost

A current trend, and one which is set to continue as a result of climate change, is an increase energy costs, especially for electricity. By providing insulation through their mass, reducing solar adsorption and transforming heat via transpiration, green roofs have a positive effect on the thermal performance of a building and it’s interior. This reduces the demand for energy intensive heating and cooling. Green roofs have been shown to be most effective at reducing the effects of high temperatures. This is relevant to many Australian buildings, which spend a large proportion of their energy budget trying to keep buildings cool.

Climate change mitigation

Green roofs can also play a role in mitigating climate change.40% of global GHG emissions are derived from building energy uses. Much of this accounts for energy used to keep buildings warm or cool, this represents a significant amount of CO2 emissions. Green roofs can help to reduce a building’s energy consumption through improving its thermal performance. By reducing the amount of energy needed to maintain a comfortable interior temperature, green roofs can have a direct impact on reducing CO2 emissions. The energy benefits of green roofs are most pronounced in reducing the demand for summer cooling. This is of especially relevant in the Australian-Asian & tropical climates and in Europe / Nth American for winter climates.

Also, since green roofs replace areas devoid of vegetation and soil, they can result in net carbon sequestration. While the amount of carbon may be small an increase in the number of green roofs over the scale on entire city can supply a meaningful carbon sink.

Economical Benefits

Reduced energy demand

The thermal properties of green roofs reduce the temperature fluctuations experienced within a building, especially during warm periods. This improves the internal environment of a building and reduces the demand for climate- modifying equipment such as air-conditioners. With a large percentage of a building’s energy budget directed towards controlling temperature, green roofs can provide significant energy savings.

Green roofs provide substantially thermal benefits to a building. Their mass, layers of trapped air, the presence of transpiring vegetation, provided shade and a substrate holding water, allow green roofs to lower the ambient temperature experienced within a building during the day. At night or in winter, these insulation properties reduce heat loss. The reduced need to heat and cool a building can lead to substantial reductions in the amount energy required to run heating and cooling units. Obviously this then reduces a buildings energy costs, saving money.

Increased roof life

Traditional roofing membranes are exposed to an array of damaging components such as Ultra-Violet light and air pollution. The presence of a green roof shields the core roofing membrane from such exposure, increasing its useful life. In fact, many cases studies are showing the presence of a green roof can increase a roof membranes life by 2-3 times.

Standard roofs are exposed to a variety of environmental extremes. They are damaged by wind and wind born particulate matter. They are constantly under attack from destructive ultraviolet radiation. Roofing materials and fixtures face corrosive pressure from pollution or marine air masses and can experience daily and annual temperature fluctuations of up to 1000C.  Green roofs can improve the life roof membrane by eliminating exposure to ultraviolet radiation, wind born particles and mechanical damage. There thermal mass reduces the fluctuations in temperature experienced when compared with a bare roof space.

In many German cities, which have had green roofs in place for over 30 years, the presence of a green roof has been shown to increase the life of a roof membrane by at least two, sometimes three times its expected life. As technology improves and current roofs age, this ratio of benefit may increase even further.

Increased property values

People have a natural affinity and appreciation for ‘natural’ elements such as vegetation. Contact with such components can induce positive emotional feelings. In terms of a property, this can increase its desirability and hence potential price. Since green roofs introduce ‘natural’ attributes to a building, they too can increase a property’s market value.

Green roofs have the potential to add substantial values, on multiple dimensions, to either the sale or rental value of a property. Studies in many western countries, including the U.S.A., U.K and Australia have shown the presence of trees around a property adds value. The value adding was attributed to positive visual amenity which these natural elements generated. Buyer preference for ‘natural elements’ has also been shown apply to green roofs. Green roofs can add value to property depending on its business-related function, for example a restaurant of bar with a green roof may be desirable trait and hence become a marketable attribute. The construction of a green roof also adds more usable floor space to a buildings specification. An increase in marketable floor space can be reflected higher prices.

As consumers become more aware of the value-adding potential of a green roof to a building, the more likely they are to pay a premium for buildings with green roof over those that don’t. Value adding components include the increased life of roof membranes and a reduction in energy costs. The environmental benefits of green roofs are also becoming important marketing tools in their own right. As large companies adopt corporate governance strategies with a substantial focus on sustainability, they are actively looking for ways to meet their environmental objectives. Increasingly, they are focusing on the premises which they tenant or buy. Such companies now have polices which mandate the environmental credentials of buildings they occupy. Buildings with green roofs deliver many of these environmental objectives, and hence are can be more desirable.

Developing industry

The green roof industry is rapidly developing within Australia growing unique knowledge and experiences. As it expands, it provides jobs for a large variety of professionals and contractors. Through the delivery of proven environmental benefits, the green roof industry and the jobs it creates are an important part of the ‘future economy’.

In Australia the green roofs industry is in its infancy, but rapidly expanding. It brings together the fields of architecture, landscape design, horticulture and engineering to deliver valuable social, economical and environmental benefits. Research and development both in the public and private sector continue to deliver new and improve technologies, products and installation methods. Installing a green roof helps to further build and promote this green industry. Continued use of green roofs helps insure that the skills and expertises in the green roof industry are maintained and developed. This leads to stronger industry and better outcomes for those requiring, designing or installing a green roof.

Alternative approach to planning/architectural requirements

Green roofs supply an innovative and novel solution to various, planning, site or client issues which may develop during a buildings construction or renovation. With their environmental credentials and amenity attributes, green roofs can provide multiple benefits while addressing and solving potential barriers.

Green roofs offer an exciting and unique design solution to many planning or client requirements. In many environmentally and atheistically sensitive sites, such as National Parks, green roofs have been successfully employed to meet strict design stipulations. With the use of indigenous plant pallets, they have been able to dramatically reduce building’s visual and environmental impact, such as a toilet block.  A significant example is the Wonthaggi desalination plant, which when completed (expected early 2012) will boast a 27,000 m2 extensive green roof (the largest in the Southern Hemisphere), reducing the large industrial plants visual impost on the surrounding costal landscape.

With increasing pressure for both new and retrofitted buildings to meet energy usage standards green roofs can be an important components of achieving a desired/required environmental outcome. In Melbourne, the Grocon Pixel Building set about to be Australia’s first carbon neutral, office building, during design it became obvious that a green roof would help it meet this objective. Green roofs can supply alternative responses to variety of planning requirements, such as open space provisions, storm water management and community space.

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