Green Roofs and Walls in Australia

1. material use 176 5.13 GREEN ROOFS AND WALLS
Green Roofs and Walls
From the turf roofs of Viking dwellings in Green roofs are an accepted part of modern PERFORMANCE SUMMARY
Scandinavia 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 their
reaching 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 green
order 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 protection
the palette of construction techniques for statutes). Australian examples are less > rapping of gaseous and particulant
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creating 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
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A green roof is a roof surface, flat or pitched,
and even to treat wastewater. roof coverings.
that is planted partially or completely with
vegetation 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 to
200mm deep) with ‘ground cover’ vegetation, Relatively easy to retrofit.
or ‘intensive’ and have a soil 200mm deep
or more supporting vegetation up to the size
of trees. Green walls are external or internal
vertical building elements that support a cover
of vegetation which is rooted either in stacked
50-200mm
pots or growing mats.
growing medium – mostly inorganic
geotextile
drainage layer
root barrier
metal / lightweight roof deck

2. 5.13 GREEN ROOFS AND WALLS 177 material use
Intensive 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 although
In between these types there are semi- there may be some mass in the soil, the
extensive (extensive with areas of deeper soil) usual growing medium is lightweight and is
and semi-intensive roofs (intensive with areas of consequently more useful as insulation rather
shallower soil). than thermal mass. Green walls have a relatively
low thermal mass for the same reason. The
supporting structure for extensive roofs (and
Green walls
green walls) is also usually lightweight, with little
Green walls are like vertical gardens and may thermal mass, whereas the structures required
be inside or outside of a building. In their for intensive roofs almost invariably employ
more elaborate form, green walls are ‘living concrete slabs or similar structures with an
walls’ and may incorporate water elements inherently high thermal mass.
including ponds and fish. Green walls may also
be incorporated into the cooling strategy of a Indoor greening can be either an extension
house, as a kind of evaporative air conditioner, of the green wall concept or can include the Insulation
and they may even be designed as part of a creation of indoor planters as integral parts of
Green roofs may or may not include an
water 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

3. material use 178 5.13 GREEN ROOFS AND WALLS
In warmer weather, green walls act like green Fire and vermin resistance The potential for food production on green roofs
roofs by reducing the surface temperature of a is being actively investigated in Australia. Led by
The soil of any green roof is fundamentally
conventional wall through evapotranspiration Central Queensland University (CQU), research
fire resistant. The different kinds of vegetation
and shading. Walls that use irrigation and includes using urban organic wastes via
that might be found on a green roof range
hydroponic techniques provide additional vermiculture for production of vegetables and
from shallow-rooted succulents that burn
cooling through evaporation. development of urban rooftop ‘microfarms’.
very poorly and offer good fire resistance, to
Shading 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 of
limiting solar gain in the summer whilst allowing Although very dry vegetation can present a Architecture recently concluded that green roofs
daylight in during winter. The insulating and low hazard, the amount of dry vegetation on an and walls can cool the local climate around a
thermal absorption properties of green roofs extensive roof is unlikely to support more building in a city by between 3.6°C and 11.3°C
also 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 to
Sound 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 them
In busy urban settings the acoustically to operate more efficiently, with energy outputs
fire resistance, particularly if it is vegetated
absorbent nature of soil and vegetation of green up to 15 per cent more than from panels on
with succulents or when the growing medium
roofs can insulate against the noise of heavy asphalt or gravel covered roofs.
is saturated. There are no relevant Australian
vehicles like trains, trams, buses and trucks.
codes as yet, but as an example, German Electromagnetic radiation can be reduced by
One office building under the flight path of San
building codes provide for 600mm fire breaks more than 99 per cent with a 100mm substrate
Francisco’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 biodiversity
transmission 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 and
An extensive thin green roof just 100mm deep
environments. They have not been identified bees has been a significant aspect of some
will reduce noise transmission by at least five
as a problem for green roofs, perhaps because overseas suburban green roofs, whilst a large
decibels.
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 dealing
Green roofs can extend the life of their with the predicted nationwide increase in peak
supporting structure and substrates. By rainfall events associated with climate change in
preventing direct solar impact on water-proofing Breathability and toxicity Australia by providing storm-water retention and
membranes, for instance, a green roof protects slowing the run-off of rainfall. Student research
Vegetation in urban areas can filter out fine
against damage from ultraviolet radiation at the University of Queensland has shown
airborne particles which then wash off into the
and from constant heating and cooling of the that run-off reductions of up to 42 per cent is
soil and foliage can absorb gaseous pollutants
membrane. A vegetated roof can extend the achievable with only 100mm of soil planted with
so it can be reasonably assumed that green
life of a conventional roof by at least 20 years moderate growth turf, and that as the soil depth
roofs provide the same services. Studies have
and reduce regular maintenance costs. Similar and vegetation water use is increased, so does
shown that green roofs can trap up to 95 per
benefits 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 been
Green roofs should be designed to last at least achieved in Australia using a green wall
50 years. Replacement of any components of Sustainability (environmental consisting of a series of three planter troughs
green roofs are relatively costly so key structural impacts) which act as filters, removing nutrients, polluting
considerations 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
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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

4. 5.13 GREEN ROOFS AND WALLS 179 material use
technologies will be driven by building rating
additional READING
systems that value green roofs and recognition
of improved market values. There has been limited reference material published
in English, and, as yet, no substantial publications
Individual properties benefit from reduced that deal specifically with Australian conditions.
maintenance and running costs and in Dunnett N and Kingsbury N (2004), Planting Green
North 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 Design
increased property values. and Construction, Schiffer Publishing, US.
Green Roofs Australia
www.greenroofs.org.au
TYPICAL CONSTRUCTION
S
nodgrass E and Snodgrass L (2006), Green Roof
On 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 Downton
2. oot barrier (polyethylene sheeting, copper
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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
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Climate]
Green walls are constructed with plants
rooted 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 or
planters. Some proprietary green wall systems Design issues
come in the form of modular panels. Plants
Structure.
may be pre-grown in these panels or planted
after the panels have been installed. Membranes.
Materials include steel for supporting Mats.
frameworks, HDPE plastic for plant
Drainage.
containers, and geotextiles. In exterior
applications, 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 to
allow for irrigation of vegetation without loss The correct growing medium for the climate
of soil and to provide reservoirs of water to and plant selection is essential, particularly
carry plants through periods of low water for extensive roofs. Plant selection for green
availability. 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.