material use 176 5.13 GREEN ROOFS AND WALLSGreen Roofs and WallsFrom the turf roofs of Viking dwellings in Green roofs are an accepted part of modern PERFORMANCE SUMMARYScandinavia to the ‘hanging’ gardens of building in Europe where some city and even The benefits of green roofs include:ancient Babylon, green roofs have a history national governments have mandated theirreaching back thousands of years. Modern use (Linz, in Austria requires green roofs on all > Longer roof lifespan.green roofs and walls are building elements new residential and commercial buildings with > Improved sound insulation.designed to support living vegetation in rooftops larger than 100m2, German greenorder to improve a building’s performance. roof building has been encouraged by the > Reduced heating and cooling requirements.Also know as ‘living’ roofs and walls, they Federal Nature Protection Act, the Building > Reduced stormwater run-off.are emerging as important additions to Code and state-level nature protectionthe palette of construction techniques for statutes). Australian examples are less > rapping of gaseous and particulant Tcreating healthy, ecologically responsible common but in 2007 a national organisation pollutants.buildings. was formed to promote green roofs and Alleviation of urban heat islands. Brisbane City Council included green roofs in its proposed action plan for dealing with Increased biodiversity. climate change. Many of these benefits also apply to green walls. Earth-sheltered houses have green roofs Green roofs are sometimes referred to as and anyone who has grown climbers across the fifth façade. There are two kinds of green a vertical trellis has had some experience in roof: intensive and extensive, each of which is creating green walls. The growing interest in appropriate for different purposes. The intensive green roof and wall construction has been roof is typically much heavier, supports more encouraged by the increasing availability of substantial vegetation and is more expensive technologies that make their construction than ‘extensive’ roofs that are often light easier and more economical. enough that they can be retrofitted to existing Green roofs are particularly effective in buildings without the need to upgrade their denser, more urban environments, where structural capabilities. they can compensate for the loss of productive landscape at ground level. ‘Green wall’ techniques can be used on homes Extensive green roofs in suburban settings as part of aesthetic Shallow growing medium – 50 to 200mm. enhancement and improving the overall climate responsiveness of individual dwellings, oof structure similar to conventional RA green roof is a roof surface, flat or pitched, and even to treat wastewater. roof coverings.that is planted partially or completely withvegetation and a growing medium over a Vegetation limited to shallow rooting plants.waterproof membrane. They may be ‘extensive’ Relatively economical.and have a thin growing medium (up to200mm deep) with ‘ground cover’ vegetation, Relatively easy to retrofit.or ‘intensive’ and have a soil 200mm deepor more supporting vegetation up to the sizeof trees. Green walls are external or internalvertical building elements that support a coverof vegetation which is rooted either in stacked 50-200mmpots or growing mats. growing medium – mostly inorganic geotextile drainage layer root barrier metal / lightweight roof deck
5.13 GREEN ROOFS AND WALLS 177 material useIntensive green roofs Appearance filters, trapping dust and absorbing pollutants like formaldehyde. Deep growing medium – 200mm or greater. Green roofs can look like anything from a lawn Requires stronger roof structure. to a forest. Extensive green roofs that use a Wide range of plantings possible. thin layer of growing medium to support ground Structural capability cover plants with short roots are generally Relatively expensive. Green roofs are usually flat but may also be designed with building performance in mind curved or sloping. Supporting structures Difficult to retrofit. rather than aesthetic concerns. Sloping and have to carry all the loads associated with the curved extensive green roofs may be seen from vegetation, its supporting medium, and the ground level. waterproofing and protective layers beneath – Intensive roofs can support quite substantial, plus any live loads from people using the roof. highly visible vegetation, cascading over the Extensive green roofs, in particular, can create sides of the building or as shrubs and trees dessicated, harsh environments for vegetation. rising above the roofline. These are commonly Often situated in urban areas, such roofs referred to as roof gardens. By creating a 200-350mm (typical) maybe more require low maintenance vegetation tolerant of landscaped surface green roofs can radically heat, cold, drought and wind. Although there change a building’s ‘roof line’. is limited experience in Australia of such roofs, Green roofs and external green walls (which can it is likely that many native plants from coastal be small and incidental or large and dramatic) and arid inland regions are suited to use in such extend the scope for creating pleasant urban demanding environments. environments by introducing plants and Green walls may be freestanding structures or greenery that are visually restful or refreshing. dependent on the building’s main structures for Proven therapeutic effects include increased support using trellises, cables or frames. paving productivity and reduced absenteeism. growing medium – lightweight manufactured soil geotextile drainage layer root barrier Thermal mass waterproof membrane (may incorporate root barrier) concrete slab There is little thermal mass in the vegetative component of green roofs and althoughIn between these types there are semi- there may be some mass in the soil, theextensive (extensive with areas of deeper soil) usual growing medium is lightweight and isand semi-intensive roofs (intensive with areas of consequently more useful as insulation rathershallower soil). than thermal mass. Green walls have a relatively low thermal mass for the same reason. The supporting structure for extensive roofs (andGreen walls green walls) is also usually lightweight, with littleGreen walls are like vertical gardens and may thermal mass, whereas the structures requiredbe inside or outside of a building. In their for intensive roofs almost invariably employmore elaborate form, green walls are ‘living concrete slabs or similar structures with anwalls’ and may incorporate water elements inherently high thermal mass.including ponds and fish. Green walls may alsobe incorporated into the cooling strategy of a Indoor greening can be either an extensionhouse, as a kind of evaporative air conditioner, of the green wall concept or can include the Insulationand they may even be designed as part of a creation of indoor planters as integral parts of Green roofs may or may not include anwater treatment system. Green walls include: the house. Green walls make it possible to have insulating layer in addition to the soil and lots of greenery without using too much floor Green facades – pots with vines on trellises. vegetation, but even without such a layer they space. Imagine walking into a room with plants provide significant thermal insulation. Overall ctive – with soil/growing medium running A covering one or more of the wall surfaces – insulation values depend on the type and up wall. living greenery on vertical surfaces can create thickness of growing medium and the type and Passive – epiphytes. quite striking impacts. extent of vegetation. There is little available Green wall systems range from arrangements documentation for R-values which will, in any of planting pots on layers of custom shelving to case, vary according to the degree of saturation sophisticated vertical layers of growing medium, of the growing medium. geotextiles and purpose made containers. Green walls can be retrofitted to existing Depending on the size of the wall, large or homes to reduce the heat load on façades. small plants can be used and the result can be The simplest kind is a trellis set with a gap manicured and elegant (think of a privet hedge) between it and its supporting wall to create or wild and funky. shade from vegetation with passive cooling Green walls can humidify and oxygenate the from transpiration of the vegetation and Mark Paul air and, depending on the plant species, can convection of heat up through the gap. further improve indoor air quality by acting as
material use 178 5.13 GREEN ROOFS AND WALLSIn warmer weather, green walls act like green Fire and vermin resistance The potential for food production on green roofsroofs by reducing the surface temperature of a is being actively investigated in Australia. Led by The soil of any green roof is fundamentallyconventional wall through evapotranspiration Central Queensland University (CQU), research fire resistant. The different kinds of vegetationand shading. Walls that use irrigation and includes using urban organic wastes via that might be found on a green roof rangehydroponic techniques provide additional vermiculture for production of vegetables and from shallow-rooted succulents that burncooling through evaporation. development of urban rooftop ‘microfarms’. very poorly and offer good fire resistance, toShading windows by deciduous vegetation more substantial plants on intensive roofs The heat island effect is reduced by green(bioshading) reduces cooling demands by that can include shrubs and even trees. roofs. Researchers at the Welsh School oflimiting solar gain in the summer whilst allowing Although very dry vegetation can present a Architecture recently concluded that green roofsdaylight in during winter. The insulating and low hazard, the amount of dry vegetation on an and walls can cool the local climate around athermal absorption properties of green roofs extensive roof is unlikely to support more building in a city by between 3.6°C and 11.3°Calso reduces the urban heat island effect. than low intensity fires. and the hotter the climate, the greater the cooling effect. The capacity of any roof-top vegetation toSound insulation support on-going conflagration is limited and a By lowering ambient roof temperatures, green green roof can be expected to have very good roofs enable solar panels mounted over themIn busy urban settings the acoustically to operate more efficiently, with energy outputs fire resistance, particularly if it is vegetatedabsorbent nature of soil and vegetation of green up to 15 per cent more than from panels on with succulents or when the growing mediumroofs can insulate against the noise of heavy asphalt or gravel covered roofs. is saturated. There are no relevant Australianvehicles like trains, trams, buses and trucks. codes as yet, but as an example, German Electromagnetic radiation can be reduced byOne office building under the flight path of San building codes provide for 600mm fire breaks more than 99 per cent with a 100mm substrateFrancisco’s International Airport, planted with a every 40m. Fire activated sprinkler irrigation can depth.mixture of indigenous grasses and wildflowers, further reduce risk.has been designed to achieve noise Habitat can be created to increase biodiversitytransmission reductions of up to 50 decibels. Vermin are offensive animals, insects and and attract wildlife including rare or migratory worms that are not wanted in human birds. Encouraging birds, butterflies andAn extensive thin green roof just 100mm deep environments. They have not been identified bees has been a significant aspect of somewill reduce noise transmission by at least five as a problem for green roofs, perhaps because overseas suburban green roofs, whilst a largedecibels. a green roof represents a deliberate effort to US manufacturer has a bee farm on the four incorporate living material into a building and hectare green roof above its new truck factory.Durability and moisture resistance create habitat in which there is less imbalance between humans and other fauna. Green roofs can reduce the costs of dealingGreen roofs can extend the life of their with the predicted nationwide increase in peaksupporting structure and substrates. By rainfall events associated with climate change inpreventing direct solar impact on water-proofing Breathability and toxicity Australia by providing storm-water retention andmembranes, for instance, a green roof protects slowing the run-off of rainfall. Student research Vegetation in urban areas can filter out fineagainst damage from ultraviolet radiation at the University of Queensland has shown airborne particles which then wash off into theand from constant heating and cooling of the that run-off reductions of up to 42 per cent is soil and foliage can absorb gaseous pollutantsmembrane. A vegetated roof can extend the achievable with only 100mm of soil planted with so it can be reasonably assumed that greenlife of a conventional roof by at least 20 years moderate growth turf, and that as the soil depth roofs provide the same services. Studies haveand reduce regular maintenance costs. Similar and vegetation water use is increased, so does shown that green roofs can trap up to 95 perbenefits derive from using green walls that add retention capacity. cent of heavy metals in the local atmosphere.an extra ‘skin’ of protection to a building. Domestic greywater treatment has beenGreen roofs should be designed to last at least achieved in Australia using a green wall50 years. Replacement of any components of Sustainability (environmental consisting of a series of three planter troughsgreen roofs are relatively costly so key structural impacts) which act as filters, removing nutrients, pollutingconsiderations include: Green roofs and walls contribute towards compounds and organic matter from the water. a wide range of sustainable development [See: 7.4 Wastewater re-use] Longevity of the structure. objectives, including: Appropriate drainage. Waterproofing. Stormwater management. Buildability, availability and cost Climate change mitigation and adaptation. Construction techniques are well understood and documented internationally with an onservation and enhancement of C increasing number of proprietary green roof biodiversity. systems available and Australian experience is Retention and binding of contaminants (bird developing rapidly. Green roofs present higher droppings or atmospheric pollution) can assist construction costs than conventional roofs removal of harmful pollution from run-off into with limited short term return on investment. aquatic ecosystems. Long term returns are potentially very good. Without legislation to encourage green roof construction, Australian uptake of the
5.13 GREEN ROOFS AND WALLS 179 material usetechnologies will be driven by building rating additional READINGsystems that value green roofs and recognitionof improved market values. There has been limited reference material published in English, and, as yet, no substantial publicationsIndividual properties benefit from reduced that deal specifically with Australian conditions.maintenance and running costs and in Dunnett N and Kingsbury N (2004), Planting GreenNorth America and the UK green roofs are Roofs and Living Walls, Timber Press, US.synonymous with quality, which is reflected in E arth Pledge (2005), Green Roofs: Ecological Designincreased property values. and Construction, Schiffer Publishing, US. Green Roofs Australia www.greenroofs.org.auTYPICAL CONSTRUCTION S nodgrass E and Snodgrass L (2006), Green RoofOn top of the structural components, there are Plants, Timber Press, US.typically seven layers to a green roof: W erthmann C (2007), Green Roof: A Case Study,1. aterproofing membrane (either built-up W Princeton Architectural Press, US. roof, single-ply membrane or fluid-applied membrane. Modified bitumen or plastic Principal author: sheeting most typical). Paul Downton2. oot barrier (polyethylene sheeting, copper R or copper compounds in the membrane).3. Insulation (optional).4. rainage layer (synthetic drainage mesh, D granular aggregate).5. Filter fabric (geotextile).6. rowing medium – also known as planting G Things to watch out for medium or substrate (manufactured soil, crushed brick or other inorganic material). When installing a green roof it is important to consider:7. egetation (shallow-rooted on extensive V roofs, deeper-rooted on intensive roofs). he climate zone. [See: 4.2 Design for T Climate]Green walls are constructed with plantsrooted in sheets of fibrous material which may Micro climate and roof orientation.be fixed to a wall or frame, or they may be Local habitats and species.constructed more like vertical arrays of pots orplanters. Some proprietary green wall systems Design issuescome in the form of modular panels. Plants Structure.may be pre-grown in these panels or plantedafter the panels have been installed. Membranes.Materials include steel for supporting Mats.frameworks, HDPE plastic for plant Drainage.containers, and geotextiles. In exteriorapplications, irrigation may be from the Trellises.top via soaker hoses or similar. Interior Plant selection.applications may use drip trays. Integration with building functions generally.Both green roofs and green walls need toallow for irrigation of vegetation without loss The correct growing medium for the climateof soil and to provide reservoirs of water to and plant selection is essential, particularlycarry plants through periods of low water for extensive roofs. Plant selection for greenavailability. roofs requires careful consideration as different conditions apply to vegetation on the roof compared with ground level and long term plant maintenance is essential. Maintenance demands are reduced by integrated irrigation, but a small green wall needs no more tending than more conventional indoor plant arrangements. Larger installations may include programmable and automated watering systems.