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British Journal of Environment & Climate Change
7(1): 43-55, 2017; Article no.BJECC.2017.004
ISSN: 2231–4784
SCIENCEDOMAIN international
www.sciencedomain.org
Life Cycle Analysis of Green Roof Implemented in a
Global South Low-income Country
Dominique Morau
1
, Tsiorimalala N. Rabarison
2
and Hery T. Rakotondramiarana
2*
1
Research Unit Piment, University of La Reunion, 117 Rue du Général Ailleret 97430, Le Tampon,
Reunion, France.
2
Institute for the Management of Energy (IME), University of Antananarivo, P.O.Box 566,
Antananarivo 101, Madagascar.
Authors’ contributions
This work was carried out in collaboration between all authors. All authors read and approved the final
manuscript.
Article Information
DOI: 10.9734/BJECC/2017/30796
Received 1
st
December 2016
Accepted 8
th
March 2017
Published 30
th
March 2017
ABSTRACT
Environmental protection becomes a global challenge currently. Green roof is one of the innovative
concepts to face this battle. An increase in its use is noticed in urban areas worldwide. But a
question arises: what are the environmental consequences of the green roofs’ life cycle? In this
paper, the environmental performance of two complete systems of lighter and heavier green roofs
implemented in a global south low-income country are analyzed and compared in order to
determine the potential impacts of both types of green roof systems. For proposing solutions
aiming at reducing environmental loads of green roofs, Life-Cycle Assessment (LCA) approach
was used in the present study. For this purpose, the approach consists of the following phases:
definition of the objective, life cycle inventory, characterization of impacts, and interpretation of
results. LCA calculations were done with the help of OpenLCA software. Results show that, non
treated materials and / or imported ones are more environmentally impactful. Hence, it is profitable
to reduce the use of cement, gravel, virgin plastics, and soil as well as imported materials whose
transport is done by plane. In addition, use of natural fertilizer for amending the growth substrate
and water from well for watering the green roof, is also recommended.
Keywords: Green roof; impact; climate change; Life-Cycle Assessment; OpenLCA.
Original Research Article
Morau et al.; BJECC, 7(1): 43-55, 2017; Article no.BJECC.2017.004
44
1. INTRODUCTION
A green roof is a roof supporting a layer of soil in
which grow vegetations. It is a green solution in
urban areas [1]. Existing for centuries before
Christ, this concept is used in many countries
such as Canada, China, United States of
America and some European countries. It has
evolved and brings a lot of benefits: allowing
energy savings for building heating in winter and
decreasing the indoor temperature in summer [2,
3], protecting and extending the life of the roof
membrane against extreme temperatures and
their fluctuations [4]. Its use also improves sound
insulation [5]; a 12 cm thick canopy layer reduces
noises by about 40 to 50dB. Moreover, green
roofs reduce the urban heat island effect as well.
Works of [6] show a mitigating urban heat island
by green roofs compared to roofs that are made
of metal, asphalt or brick. The use of green roofs
significantly contributes to the retention and
purification of rainwater [7,8]. It also allows a
capture of carbon dioxide and an improved air
quality. Besides, a sharp increase of human
activities on the exploitation of natural resources,
manufacturing materials, transportation and
urban construction, can be noticed. The amount
of newly discovered resources continues to
decline due to their limited and non-renewable
characters [9]. Urban buildings are increasing
and creating adverse effects on the environment
[10]. Green roofs can be adopted to overcome
these problems. Particularly regarding
Madagascar, this big island is in a critical
situation from an environmental perspective. The
aforementioned benefits of green roof can
contribute to reducing pollution problems in
urban areas of Madagascar. However, it is
essential to know the consequences of its
implementation and usage.
Life-Cycle Assessment (LCA) increasingly
becomes indispensable for having more
environmentally friendly design of buildings as
reported by review papers [11,12]. Several
studies on the LCA of green roofs are currently
available in the literature. The first two works
implementing LCA methods were conducted by
Saiz et al. [13] and by Kosareo and Ries [14] for
showing the environmental benefits provided by
green roofs in comparison with that related to
conventional roofs. The former, who totally
neglected the disposal phase of green roofs,
found that cumulative annual energy savings
caused by replacing the conventional flat roof
with a green roof, allows reducing environmental
impacts by between 1.0 and 5.3%. On the other
hand, the latter issued that though energy
savings due to green roof’s lower thermal
conductivity are relatively modest with respect to
the overall building energy use, it is significant for
environmental impact over the life cycle of the
building. Peri et al. [15], while applying LCA to
extensive green roof, focused their attention on
the disposal of substrate and on the impacts of
fertilizers used during the operational phase,
which seem to play an important role in the
whole LCA balance. Besides, Tselekis [16]
highlighted the potential energy savings and
environmental benefits due to the use of green
roofs by comparing construction costs and taking
as references the conventional insulated and
non-insulated roofing systems. Hong et al. [17]
applied 16 improvement scenarios based on
green roof systems in combination with energy-
saving measures for various weather conditions
in South Korea; some of these scenarios were
proven to be cost-effective. Blackhurst et al. [18]
used LCA to assess the widespread installation
of green roofs in a typical urban mixed-use
neighborhood by taking into account the market
prices of materials, construction, energy
conservation, storm-water management, and
greenhouse gas (GHG) emission reductions;
results reveal green roofs are currently not cost
effective on a private cost basis, but multifamily
and commercial building green roofs are
competitive when social benefits are included.
In addition, a certain number of LCA were carried
out to evaluate the environmental impacts of
various green roof constituent materials. For
instance, while focusing their LCA work on
polymers whose manufacturing process causes
emission of harmful elements such as NO
2
, SO
2
,
O
3
and PM10 into air, Bianchini and Hewage [19]
reported that the aforementioned air pollution can
be balanced by the green roof’s pollution removal
capacity in 13-32 years. However, they
recommended that low density polyethylene and
polypropylene have to be replaced in the green
roof component materials as their manufacturing
process has many other negative impacts to the
environment than air pollution. Rivela et al. [20],
while applying LCA methods on different green
roof constituent materials, found that the support
layer which is made of concrete slab is the most
impactful in all impact categories with the
exception of the ozone layer depletion category;
the most important impact contribution being due
to thermal insulation made of concrete tile with
extruded polystyrene and to felt wick irrigation
system. Moreover, it is worth noting the work of
Molineux et al. [21] though the utilized method
Morau et al.; BJECC, 7(1): 43-55, 2017; Article no.BJECC.2017.004
45
was not exactly LCA, as they environmentally
characterized four recycled materials that have
been manufactured into useful substrates for use
on extensive green roofs. While choosing the
crushed red brick as an industry standard
substrate control, three alternative pellets made
from: clay- sewage sludge - fly ash mixture,
recycled newspapers’ ash, and carbonated
limestone. Results revealed that these alternative
substrates have great potential in the green roof
market as they are as good, if not better, than the
industry standard, both economically and
environmentally.
Additionally, Chenani et al. [22] implemented
LCA to two types of extensive green roof for
determining the potential environmental impacts
of different layers composing these green roofs.
Their results highlighted that the water retention,
drainage and substrate layers contained the
most negative impactful components. Hence,
they recommended the design of simple green
roof systems whenever feasible as well as the
use of recycled and local materials rather than
virgin ones and those requiring long distance
transports; use of compost on green roof is also
recommendable as composting organic wastes
seems better than landfill disposal; anyway, the
use of Rockwool, virgin HIPS (High-Impact
PolyStyrene) and expanded clay should be
avoided. Rincón et al. [23] assessed, the
environmental impact and the benefits of using
recycled rubber crumbs from out use tires as a
drainage layer in extensive green roofs, with the
help of LCA in which performances of green
roofs versus conventional ones were compared
while considering the production, construction,
operational, and disposal phases of roofing
systems. It was concluded that the studied
recycled rubber is environmentally friendly
constructive material that should be
recommended for use in buildings. Gargari et al.
[24] focused their LCA work on the green roof
soil for assessing the relevance of different
growing medium types on the environmental
impact of a green roof. It was concluded that
adopting a proper design of the growing medium
soil by taking into account all maintenance
operations is crucial for a good green roof
design. For that purpose, more complete
information (such as thermal and water retention
properties) about the growing medium available
on the market are desirable.
Lamnatou and Chemisana [25] undertook LCA to
evaluate environmental impact of a Photovoltaic
(PV)-green roof along with other roof
configurations: PV-gravel, green (extensive and
intensive), gravel. While material manufacturing,
material transportation, use/maintenance and
disposal phases being considered in the LCA,
the results revealed that material manufacturing
is the most energy-demand phase for all the
studied roofs and the additional environmental
impact characterizing the PV-green system in
comparison with the PV-gravel one can be
balanced on a long-term basis. Then, Lamnatou
and Chemisana [26] could determine the critical
point after which PV-green roof becomes more
eco-friendly than the other PV roofs by means of
ReCiPe methodologies [27,28].
As LCA software tools, commercial products,
especially SimaPro [29], are the most used for
the aforementioned LCA studies [13,14,19,23,
24]. As for the present work, environmental
impacts of extensive and intensive green roofs
located in a low-income country were assessed
according to ISO 14040 [30] and ISO 14044 [31]
standards. More precisely, special attention was
paid on the impact of material transportation as
the building location is in Antananarivo
Madagascar. For that purpose, Ecoinvent v3.1
database [32] was used as database tool
while OpenLCA [33] which is open source
software freely available online was utilized as
LCA tool.
Hence, this work aims at providing potential
solutions for improving the environmental
features of the green roof design and the
manufacturing of materials used in its various
component layers by using free LCA tools.
That should enable to identify the best
implementation scenario among various possible
ones.
It is worth reminding that extensive green roof is
lightweight while intensive one is a heavyweight
version. From the bottom to the top layer, green
roofs whose LCA is carried out in this study are
assumed to be made of: a concrete, metallic or
wooden structure for supporting all the other
layers of the green roof, an impermeable
membrane (synthetic rubber), an anti-root
protection (polyethylene), a layer of draining and
filtering (polyethylene), a growth substrate layer
(soil and fertilizer) and a canopy layer (grass,
sedum, shrub). Though polyethylene is among
materials that should be replaced according to
recommendations formulated by [19], it was used
in the present study as there is no low cost
replacement material available in the market on
the basis of the authors’ knowledge.
Morau et al.; BJECC, 7(1): 43-55, 2017; Article no.BJECC.2017.004
46
2. MATERIALS AND METHODS
LCA is a systemic multi-criteria environmental
approach. It only handles environmental impact
of a product and ignores financial, political or
other aspects. It consists of the following steps:
1) definition of the aim and scope of the study, 2)
life cycle inventory, 3) characterization of
impacts, and 4) interpretation of results [30]. It is
based on the inventory of inputs (for example,
raw materials, transport, process of energy
conversion for the manufacturing and production
of the studied product) and outputs (for example,
emission of substances in soil, in water and in
air). Hence, the potential impacts of each
constituent layer of both aforementioned green
roof types are evaluated and compared using
this approach.
2.1 Aim and Scope of the Conducted LCA
The objective of the conducted LCA is to identify
adverse effects of various constituent layers of a
unit surface of green roof that is located in
Antananarivo Madagascar, to the environment,
human health and resource use. Then, solutions
and remedies are especially proposed for
mitigating these adverse impacts.
The functional unit adopted in this study is "the
construction, the transmission and the use of 1
m
2
of green roof for a period of one year, five
years and ten years". A priori we have two types
of green roof having a large difference of
properties in terms of the amount of used
products; the study of both cases allows a
comparison and provides insights that help us
either to improve green roof implementation or at
least to have information for finding which kind of
green roof is more convenient.
With respect to the system boundary, while
mounting and end-of-life phases of the green
roof being excluded, the following ones are
included in the present study: manufacture and
transport of various layers as well as the use of
green roofs. In background, we have: the
extraction of raw materials, energy conversion
and supply, and waste production during the
manufacture of various green roof layers. These
data are already included in our database. Fig. 1
depicts the lifecycle process of green roofs and
the system boundary.
The characterization methodology of impacts we
have used in the simulation is the CML Baseline
method, which is developed by the Institute of
Environmental Sciences (CML) of the University
of Leiden in Netherland, in the OpenLCA
software [33]. This modeling method
corresponds to the first order effects: quantifiable
and relatively straightforward, thus with small
uncertainty but little talking [34].
Fig. 1. Lifecycle process of green roofs and the system boundary
Morau et al.; BJECC, 7(1): 43-55, 2017; Article no.BJECC.2017.004
47
2.2 Life Cycle Inventory
As being mentioned previously, OpenLCA
software [33] was used to achieve all simulation
steps. All used data are identified from different
companies and experts while referring to the
green roof design guidelines that are proposed
by Peck and Kuhn [35] which shows the amount
of materials used in the design of green roofs.
Ecoinvent (version 3.1) database [32] from which
resources come is adjoined into this software.
For carrying simulations, green roof was
assumed to be constituted by some layers as
illustrated in Fig. 2. For the characteristics of
these different layers in the scenarios, we used
data from [36].
Fig. 2. Various layers constituting a green
roof
2.2.1 Extensive green roof scenario
2.2.1.1 Canopy layer
The canopy layer is the most essential part of the
green roof. While the adopted support being
lighter as can be seen in further subsection, the
selected vegetation for this kind of roof is
herbaceous, more precisely grass, as it is very
variable in quantity and grows over time. For
this study, a unit area of the canopy layer is
made of about 1 kg of grass having a thickness
of 0.02 m.
2.2.1.2 Growth substrate layer
The growth substrate layer is also essential for
the green roof as it serves the nutrition of
vegetation and plays an important role in
managing storm water. For this first type of green
roof, the substrate is made of soil that is mixed
with compost in the ratio of 100 kg and 25 kg
respectively, while having a thickness of 0.15 m.
2.2.1.3 Protection layer
The protection layer is composed of two plastic
materials. The first one is anti root barrier made
of high density polyethylene: 0.76 kg of weight
and 0.0008 m of thickness. This layer is needed
to prevent root penetration into the support. The
other one is a layer of drainage and filtration
consisting of virgin polystyrene: 0.68 kg of weight
and 0.008 m of thickness. The filter is used to
filter fine particles from the substrate while the
drainage layer which looks like an egg box allows
the free flow of water.
2.2.1.4 Support layer
Pine wood was selected as material of the
support layer which is vital as it supports all the
above mentioned different layers of the green
roof; it weighs 25 kg (per unit surface) and is
0.15 m thick. Table 1 lists the transport of
materials for extensive green roof.
Maintenance items on the functional unit during
the roof-use are watering and addition of
substrate on the canopy and soil layers. In terms
of resources, 20 kg of fertilizer and 96 kg of
water per unit area of the green roof should be
added. With the help of database, the following
process was considered "Tap water production
underground water without treatment - Rest-of-
the-World (RoW)" and "Field application of
compost-RoW". The quantities of required inputs
are calculated according to the use period of the
considered product.
Table 1. Transport of extensive green roof materials
Layer Transport, freight,
lorry 3.5-7.5
metric ton,
EURO3-RER*
Transport, freight,
lorry 3.5-7.5 metric
ton, EURO3-RoW*
Transport, freight,
light commercial
vehicle-RoW*
Transport,
freight, sea,
transoceanic
ship-GLO*
Canopy - - 30 km -
Substrate - - 20 km -
Protection 225 km 365 km 20 km 8938 km
Support - 168 km 20 km -
*Abbreviations being region codes used by ecoinvent for indicating the geography such that:
Global (GLO), Europe (RER), the Rest-of-the-world (RoW)
Morau et al.; BJECC, 7(1): 43-55, 2017; Article no.BJECC.2017.004
48
2.2.2 Intensive green roof scenario
The component materials of intensive green roof
are listed in Table 2. It was assumed that only
support and protection layers change during
transport.
For the support layer, cement undergoes two
types of transport: one by truck and another one
by commercial car, over distances of 190 km and
20 km respectively. Additionally, we made the
assumption that steel comes from South Africa,
by 4 types of transportation means: rail, sea,
truck and commercial car over distances of 210,
2617.92, 365 and 20 km respectively. Gravels
are transported by road on a commercial
transport route over 20 km.
With respect to the protection layer, after a
commercial car transport of about 20 km to the
airport, it is conveyed by aerial transport from
Europe to Antananarivo of 5655 km of distance,
and then it is again transported by commercial
car over a distance of 50 km.
In addition, 150 kg of fertilizer and 730 L of water
are added to the green roof annually. The
process data that are taken into account in the
present study are related to the production of
cement, steel, gravel, polyethylene, polystyrene,
wool, cracked tile, fertilizer, and bush.
2.3 Impact Assessment
This step converts inventory data in indicators
that characterize the potential effects on human
health and on the environment of the considered
product during its life cycle [28]. We used the
latest version of CML Baseline method. It
presents ten categories of environmental
impacts, but we only present 3 that are of interest
and relevant to the case of Madagascar as
shown by Table 3.
Table 2. Component materials of intensive green roof
Layer Product Material Weight
(kg.m
-2
) Thickness
(m)
Support Concrete
Cement
Steel
Gravel
75
25
150
0.15
Protection
Anti-root barrier
Recycled LDPE (Low
Density PolyEthylene) 0.175 0.0002
Drainage and
filtration Recycled HIPS (High-
Impact PolyStyrene) 1.252 0.05
Water reserve Hydrophilic mineral wool 6 (dry)
46 (saturated) 0.0275
Substrate Mixture of recycled
soil and organic
fertilizer
Crushed tile
Poultry manure 200
50 0.40
Canopy Vegetation Low growth bushes 10 1
Table 3. Descriptions of selected impact categories
Category of impact Indicator Unit Description
Climate change
GWP100 (Global
Warming Potential) Kg CO
2
eq. The product’s impact on
global warming over 100
years.
Depletion of abiotic
resources
Fossil fuels MJ Characterization of
emissions of greenhouse
gases in the air.
Human toxicity HTP inf. (Human
toxicity Potential) Kg 1.4-
dichlorobenzene
eq.
The potential effect on
humans of toxic
substances emitted into
the air, water and soil.
Morau et al.; BJECC, 7(1): 43-55, 2017; Article no.BJECC.2017.004
49
We chose the Global Warming Potential (GWP)
with a 100 year time horizon as it is the most
widely used indicator. It represents the duration
of human life and was selected in the Kyoto
Protocol Article 5-3. We also need a long time
span to see the change caused by global
warming (for example: increase of sea levels).
3. RESULTS AND DISCUSSION
3.1 Phase 1: Production of Various Green
Roof Constituent Layers
Simulation results obtained from OpenLCA [33]
are presented in Table 4 which compares
production impacts of various constituent layers
of both considered green roof types.
Compared to wood use, cement production
impacts 53 kg CO
2
equivalent more while steel
manufacturing causes only 5.3 kg CO
2
equivalent of additional impacts. In terms of
resource consumption, cement production
consumes 15 times more compared to steel
fabrication. On human toxicity, cement
production is always the most impacting with a
value of 5.288 kg 1.4-dichlorobenzene
equivalent. Generally, impacting substances are
those that are released during various stages of
production or transport rather than those
contained in the product unless they are toxic
ones. Cement is produced by combustion of
limestone and other additives at very high
temperatures. Such combustion rejects flying
ashes and fine mineral particles which can be
carcinogenic to humans [37].
Table 4. Comparison of production impacts of both green roof types’ layers
Layer Category of impact* Climate
change -
GWP100**
(Kg CO
2
eq.)
Depletion
of abiotic
resources
(MJ)
Human toxicity -
HTP inf.**
(Kg 1.4-
dichlorobenzene eq.)
Support Woodwool production-RoW* -15.861 11.087 0.368
Gravel production, crushed-RoW 0.657 8.026 0.631
Cement production, pozzolana
and fly ash 11-35%, non-US** 89.148 318.375 7.931
Steel production, low-alloyed, hot
rolled-RoW* 2.905 36.949 2.777
Substrate Field Application of compost-
RoW* 19.982 260.66 10.479
Land already in use, arable land-
GLO* 40.625 84.084 10.372
Field application of poultry
manure –RoW* 4.136 257.329 13.172
Concrete roof tile production-
RoW 59.7 357.748 17.224
Protection
Polyethylene production, linear
high density, granulate-RER* 1.494 50.589 0.064
Polyethylene production, low
density, granulate-RER* 0.333 10.303 0.018
Polystyrene foam slab
production, 100% recycled-RER* 0.461 6.477 0.142
Polystyrene, high impact –RER* 2.307 51.446 0.215
Woodwool production-RER* -3.45 5.929 0.266
Canopy Grass production, permanent
grassland, organic, extensive-
RoW*
-2.746 1.081 1.081
Grass production, organic,
intensive –RoW* -6.277 2.471 0.029
*Geographical codes used by ecoinvent [32]: GLO (Global), RER (Europe), RoW (Rest-of-the-world);
** GWP100 (Global Warming Potential), HTP inf. (Human Toxicity Potential), US (United States)
Morau et al.; BJECC, 7(1): 43-55, 2017; Article no.BJECC.2017.004
50
For the protection layer: materials that are used
for extensive green roof are more impacting
compared to those related to intensive green
roof. Indeed, high density materials which require
more resources are employed for extensive
green roof. These materials are more impacting
due to their impurities which contain noxious and
polluting substances. The use of recycled
materials and low density has less impact. For
example, polystyrene which comes from
benzene hydrocarbon is toxic if inhaled.
However, the recycled polystyrene is less toxic
as more than 60% of the aforementioned
pollutants are already eliminated in the recycling
process.
With regard to the substrate layer: the choice of
substrate components is an important part in the
implementation of a green roof. It can be noted in
the inventory that the substrate amount of
intensive green roof is twice that of the extensive
green roof. Then in the climate change section,
the use of crushed tile is beneficial as this
material is recycled; it enables to halve the
amount of the required substrate, for example.
Nonetheless, the use of soil is more
advantageous in terms of resource consumption.
This is due to energy consumption related to the
tile crushing. For the choice of fertilizers, here the
use of the material for intensive green roof is
twice that for extensive green roof. However, the
global warming category result shows that the
use of compost is 5 times more impacting than
the use of manure from poultry. For resource
depletion, compost consumes twice more
resource for identical amounts of material
contained in both kinds of manures. All this
comes from the production, transportation and
spreading of compost which requires the use of
mechanical and motorized vehicles which are
major consumers of resources and are sources
of pollutant emissions (carbon dioxide and fine
particles) in large quantities. Compost is not
intended for use on green roofs initially, but it
enables to avoid landfill disposal [22]. Thus, it is
better to use natural products requiring no
treatment as fertilizer.
With respect to canopy layer: for all impact
categories, we can see from these results that
the environmental impacts are proportional to the
amount of used vegetation for the roof type.
Therefore, the intensive green roof presents
more impacts than the extensive one. Inversely,
this latter has negative effects on climate
change, which are advantages.
3.2 Phase 2: Transportation of Materials
to the Building Site
Fig. 3 presents the comparison of material
transportation impacts for both green roof types.
Fig. 3. Comparison of material transportation impacts for both green roof types
Morau et al.; BJECC, 7(1): 43-55, 2017; Article no.BJECC.2017.004
51
For all categories of impact, transportation of the
intensive green roof support layer causes 8 times
greater impact than that related to the extensive
green roof one. For intensive green roof,
transportation of various materials is done by 3
types of transport: aerial, maritime and terrestrial,
which not only involve very high value of climate
change through emission of greenhouse gases
but also consume fossil resources and release
environmental pollutants. Indeed, these
transportations emit into the atmosphere
substances such as nitrogen oxide (NO) and
sulfur dioxide (SO
2
) with different emission rates.
The impact of transportation is here dominated
by maritime transport. To transport the protection
layer, that related to intensive green roof is more
impacting as aerial transport is used.
Emissions from the abovementioned
transportations contribute to increasing the
concentration of greenhouse gases in the
atmosphere. They are responsible for the
retention of heat as well as the diffraction of
radiation contributing to climate change. On
resource depletion, fuel consumption is more or
less proportional to the traveled distance. With
regard to human toxicity, the aircraft causes
higher emissions compared to other types of
transport means. Indeed, today's aircraft release
high amounts of CO in the troposphere and
stratosphere, which is hazardous to human
health.
The travelled distances for the transportation of
the respective substrate layers of both green roof
types are identical but the amounts of
transported materials are different, as
transportation of the substrate layer for the
intensive green roof is twice more impacting, that
is, the impact is double for each impact category,
than that related to the extensive one.
The transportation of the canopy layer is done by
trucks. The impact is dependent on the load and
the distance; the heavier is the load, the more
pollutant is the transportation.
3.3 Phase 3: Use Phase
While the previous subsection results show that
the use of intensive green roof is environmentally
more impactful than the extensive green roof
because of the difference of used materials and
their amounts, the present subsection aims at
scrutinizing the resource consumption according
to the use patterns of both roof types in order to
choose materials that allow saving resource.
As can be seen once more from Fig. 4, for every
category of impact, intensive green roof is
environmentally more impactful than the
extensive green roof for all considered use phase
lifetime span. Besides, impact magnitude on
climate change of intensive green roof for
5-year use phase is almost equivalent to that
related to 10-year use phase of extensive green
roof.
As being outlined previously, maintenance
process mainly consists of adding fertilizer and
watering periodically. The use of fertilizer from
poultry is more advantageous over the compost
use as fertilizer made of chicken droppings is
produced on site without biological treatment
which can lead to high energy consumption.
Moreover, it also is convenient to water the green
roof canopy with well water which can be
pumped, for example, by photovoltaic devices.
3.4 Suggestion of Some Solutions
In this subsection, some improvement solutions
for mitigating potential impacts are suggested.
Some information allowing the choice of
materials and means of transport to be used are
presented as well.
To have a much lighter structure, a steel
structure whose impact has already been studied
by Olmez et al. [38] can be used instead of a
concrete structure. However, it is better to
choose wood for its ability to store CO
2
[39]. The
fact of using less plastic materials reduces the
impact of the protection layer. It is beneficial to
use manually crushed tile mixed with chicken
droppings for the substrate layer. Whatever the
vegetation types, the canopy layer is always of
interest through its capacity of CO
2
storage and
dust collection.
Several means of transport were presented
during the inventory. Air transport is dominant
overall impact categories as it emits GHG and
pollutants up to 8 times greater than maritime
transport for the same quantity of carried loads.
Besides, the amount of GHG emission related to
intensive green roof protection layer is here 8
times greater than that of extensive green roof
one. Although transportation has been included
in previous studies (Kosareo and Ries [14]), its
total environmental impact has not been
quantified explicitly. In the present study, it has a
very important part of impacts. As optimization
solution, production in situ of materials is
suggested.
Morau et al.; BJECC, 7(1): 43-55, 2017; Article no.BJECC.2017.004
52
Fig. 4. Comparison of impacts during use phases of both green roof types
Adding the growth substrate and watering are
always crucial when using green roofs.
Therefore, their impacts are also to be
considered. According to the above presented
results, the impact of the use phase of intensive
green roof is more important than that of the
extensive green roof. Additionally, the poultry
manure remains the best fertilizer as the quantity
of added elements in intensive green roof is
more than those related to the extensive green
roof. One can assert that the impact of each
material depends on its amount, its transport and
especially of its characteristics. According to
Fertilizers Europe and UNIFA (Union des
industries de la fertilisation), finding an
alternative to traditional fertilizer is important as
composting waste products would be profitable.
Hence, there is a sensitization for the use of the
ammonitrate (an ammonium nitrate-based
mineral fertilizer) that could reduce the carbon
footprint by up to 25% [40]. And finally, the use of
well water rather than tap water is advantageous
for saving resource and energy.
4. CONCLUSION
The environmental performance of both
lightweight and heavyweight green roof systems
was analyzed to determine their potential
environmental impacts. For that purpose, the
respective impacts of different materials,
transport and use of layers constituting the green
roofs were calculated using free LCA tools.
Based on the obtained results, it is possible to
develop simple green roof systems using as
less artificial materials as possible. Under the
adopted assumptions in the present study,
recycled products should be used instead of
natural ones.
With respect to materials, it is better to choose
lightweight materials from the support layer to the
canopy layer. Improvements of the most
impactful materials such as those used for the
protection stratum and the substrate layer should
be considered.
As far as transportation is concerned, it is
reasonable to make maximum use of local
products in order to avoid the high environmental
impacts of international transport.
With regard to energy and resource consumption
during the use phase of green roof: it can be
asserted from the obtained comparison results
that there is a huge difference between using
compost and chicken manure as fertilizer in the
substrate layer; it is more beneficial to utilize
chicken manure. Moreover, the use of well water
is also recommended for watering.
Morau et al.; BJECC, 7(1): 43-55, 2017; Article no.BJECC.2017.004
53
ACKNOWLEDGEMENTS
The authors of this work are grateful to
Bienvenue Raheliarilalao for her assistance on
the use of LCA tools.
COMPETING INTERESTS
Authors have declared that no competing
interests exist.
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