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Economic Benefits and Costs of Green Roofs

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Reflections Green roofs are well-known as a sustainable construction practice. Economical benefits of green roofs have been widely discussed by many researchers. This chapter starts with an extensive literature review on the benefits and costs of green roofs. The quantitative estimates of individual and public benefits of green roofs were conducted, and lifecycle costs of green roofs from cradle to grave were analyzed. The net present values per unit area of a green roof were accessed by considering the individual benefits, public benefits, and lifecycle costs. A comparable assessment was performed to evaluate the payback period of green roofs in different markets. The analysis demonstrated that the lifecycle cost of green roofs can be paid back by individual benefits in a mature market. If the public benefits are added into the assessment, the lifecycle cost of green roofs can be retrieved in most of the markets.
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Chapter 4.5
Economic Benefits
and Costs of Green Roofs
Haibo Feng and Kasun N. Hewage
Chapter Outline
Introduction 307
Individual Benefits of Green Roofs 308
Energy Reduction in Heating and
Cooling 308
Membrane Longevity 308
Acoustic Insulation 308
Aesthetic Benefits 309
LEED Certification Bonus 309
Public Benefits of Green Roofs 310
Reduction of Stormwater Runoff 310
Improvement of Air Quality 310
Mitigation of Urban Heat Island
Effect 311
Increment of Urban Biodiversity 311
Life Cycle Cost of Green Roofs 311
Initial Cost 311
Operation and Maintenance (O&M)
Cost 312
Disposal Cost 312
Green Roof Cost Benefit Assessment 313
Net Present Value and Payback
Period 313
Scale of Implementation 314
Green Roof Policy Initiatives 315
Conclusion 315
References 316
INTRODUCTION
Green roofs are well-suited for urban areas, as they provide excellent value
for money at both individual and public levels in comparison with other cur-
rently available green or gray infrastructure. However, the high initial invest-
ment required for green roofs acts as a barrier to their market penetration. In
general, individual benefits of green roof include reduction in energy use for
heating and cooling, membrane longevity, acoustic insulation, aesthetic bene-
fits, and LEED certification bonus (Berardi, 2016; Clark et al., 2008; Nurmi
et al., 2013; USGBC, 2015; Bianchini and Hewage, 2012). Public benefits
include reduction of stormwater runoff, improvement of air quality, mitiga-
tion of urban heat island effect, and increment of urban biodiversity, etc.
(Driscoll et al., 2015; Connelly and Hodgson, 2008; Rosenzweig et al., 2006;
Brenneisen, 2006). The costs in green roofs involve their initial construction,
operations, maintenance, demolition, and disposal (Bianchini and Hewage,
307
Nature Based Strategies for Urban and Building Sustainability.
DOI: https://doi.org/10.1016/B978-0-12-812150-4.00028-8
©2018 Elsevier Inc. All rights reserved.
2012). The objective of this chapter is to present the economic benefits of a
green roof in terms of its public and individual benefits, summarize the total
costs of a green roof throughout its lifecycle, and estimate the payback
period based on the benefits and costs.
INDIVIDUAL BENEFITS OF GREEN ROOFS
Energy Reduction in Heating and Cooling
Green roofs reduce energy consumption in space heating through shading,
evapotranspiration, insulation, increase in thermal mass, and reduction of
heat loss through radiation. Green roofs can also be more efficient in pre-
venting heat loss in the winter compared with conventional roofs (Liu and
Baskaran, 2003; Berardi, 2016). The reduction in energy bills is usually the
most convincing factor for building owners to install green roofs. For exam-
ple, an experiment conducted in Ottawa found that a 6-inch extensive green
roof reduced heat gains by 95%, and heat losses by 26% compared to a con-
ventional roof (Liu, 2002). Another study on a two-story building was con-
ducted by Florida Solar Energy Center. Its findings revealed that 18% of
energy used for space cooling was saved by a green roof compared with the
conventional roof, and 44% was saved when the plants were more estab-
lished (Sonne and Parker, 2006). The economic benefit of reduction in space
conditioning demand has been quantified by a previous study, which demon-
strated that a green roof can save $0.180.68 m
2
in cooling, and 0.22 m
2
in heating annually (Bianchini and Hewage, 2012).
Membrane Longevity
Green roof technology increases the lifespan of a building’s roof by protect-
ing against diurnal fluctuations, UV radiation, and thermal stress. Studies
have revealed that the lifetime of roofing membrane can be easily lengthened
up to 4050 years by green roofs (Clark et al., 2008), while a conventional
roof’s lifespan ranges from 10 to 30 years (Oberndorfer et al., 2007). The
cost of replacing a conventional roof at the end of its lifespan is estimated at
around $160 m
2
(Bianchini and Hewage, 2012). The benefit of installing a
green roof is the cost of installing a conventional roof 20 years in the future,
which is at $160 m
2
.
Acoustic Insulation
Green roofs improve the soundproofing of a building, and reduce the sound
reflection by increasing absorption (Azkorra et al., 2015). For buildings
located near very strong sources of noise such as night clubs, highways, or
flight paths, the sound insulation created by green roofs can be especially
308 SECTION | IV Nature Based Strategies: Social, Economic and Environmental
useful. There are no reliable estimates in the literature about the economic
value of the sound insulation benefit of green roofs. A commonly used tech-
nique to improve noise insulation is to apply an extra layer of plasterboard
into the ceiling. The noise insulation benefits acquired due to green roofs are
similar or higher than that gained by such an additional ceiling element,
since green roofs have more than one layer (Connelly and Hodgson, 2008).
Material and installation costs are approximately $29 m
2
(h20 m
2
) for
plasterboard. Therefore, the noise insulation benefit of green roofs is also
estimated to be around $29 m
2
in air noise zones (Nurmi et al., 2013).
Aesthetic Benefits
Aesthetics are the most intangible benefit, generally left out in cost-benefit
analyses due to the difficulty in valuing aesthetics in monetary terms. An
individual’s willingness to pay a higher price can be used as a method to
attribute a monetary value to qualitative characteristics such as aesthetics.
Commission for Architecture and the Built Environment in London states
that the price of buildings or houses will increase by 6% if there is a park
nearby, and by 8% if the building has a direct view of the park. Green roofs,
especially if spread over a larger area, has a similar function as a local park.
Accordingly, 2%5% and 5%8% of property value increments for exten-
sive and intensive green roof respectively have been assumed (Bianchini and
Hewage, 2012). The extensive green roof may raise property value from
$2.6 to $8.3 m
2
, while intensive green roofs may increase property value
from $8.3 to $43.2 m
2
. Besides the aesthetic benefits, green roofs can also
provide recreational spaces in urban areas if they are designed for public use
similar to parks.
LEED Certification Bonus
LEED certified buildings are gaining in popularity because of their lower
operating costs, better employee performance (in commercial and industrial
buildings), improved public relations, better health standards, as well as other
community benefits (CaGBC, 2014). The most attractive aspect for owners
is that it increases access to capital. It is estimated that the return-on-interest
of LEED certified buildings improved by 19.2% on average for green retrofit
projects in existing buildings, and 9.9% on average for new green construc-
tion projects (USGBC, 2015). Under the Canada Green Building Council
LEED program, buildings with green roof installations gain one point for
stormwater management, and one point for reducing heat island effect if the
roof covers at least 50% of the building. Another benefit of green roof tech-
nology is that the vegetation and soil media of green roof can be used as a
filter for the storm runoff, so that the water from the green roof system can
be used to irrigate other landscaping features without pretreatment (LEED
Economic Benefits and Costs of Green Roofs Chapter | 4.5 309
Canada, 2009). Under the LEED scheme, this may warrant an additional
point for water efficient landscaping. The ability to reduce energy demand
for cooling and heating, and increased energy efficiency may also garner
additional points for optimized energy performance. Furthermore, potential
points can be gained for reduced site disturbance, protection or restoration of
open space, and innovation in design.
PUBLIC BENEFITS OF GREEN ROOFS
Reduction of Stormwater Runoff
Green roofs can impact the stormwater retention capacity of buildings. Most
importantly, with the presence of green roofs, the rainwater that falls onto
the roof surfaces flows into the sewers at a slower rate, as green roofs are
able to retain water. Depending on regional climate, green roofs can lower
the sewer system capacity requirement, by holding as much as 50%95%
of annual rainfall precipitation (Driscoll et al., 2015; Beecham and
Razzaghmanesh, 2015). An investigation by the city of Portland revealed
that $30 m
2
year
1
is needed to manage the stormwater falling on impervi-
ous areas that do not absorb rainwater (City of Portland, 2008). Based on the
retention performance of green roofs listed above, green roofs will be able to
create $1528 m
2
savings per year by reducing the public infrastructure
management fees.
Improvement of Air Quality
Green roofs are recognized as an air quality control technology. The vegeta-
tion reduces air pollution by actively absorbing many pollutants, and by pas-
sively filtering and directing airflows. It was estimated that eight metric tons
of unclarified air pollutants can be removed per year by 109 ha of green
roofs in Toronto, Canada (Currie and Bass, 2010). Another study conducted
in Chicago estimated that the annual mass of air pollutants which can be
removed by 19.8 ha of green roofs amounts to 1675 kg (Yang et al., 2008).
The cost estimate for the air quality benefit of a green roof is calculated
by considering the negative effects of pollutant on health, environment,
infrastructure, and climate change. The cost would be significantly higher in
urban environments, due to the effect on a larger number of people. In North
America, the NO
x
emissions tax is $3375 ton
1
(Clark et al., 2008). In
Europe, the SO
x
cost in a populated area is $2500 ton
1
, and $500 ton
1
for
NO
x
cost (Nurmi et al., 2013). Based on the results from Yang et al. (2008)
and Clark et al. (2008), the benefits from the improvement of air quality
would be around $0.03 m
2
annually assuming all the air pollutants removed
by green roof are NO
x
.
310 SECTION | IV Nature Based Strategies: Social, Economic and Environmental
Mitigation of Urban Heat Island Effect
In urban environments, vegetation has often been replaced by impervious
and dark surfaces. Dark surfaces reflect less solar radiation and absorb more
energy. Due to the lack of vegetation and the presence of dark surfaces, the
urban heat island effect is created. A simulation study in New York showed
that the average roof temperature can be reduced by as much as 0.8Cif
50% of the roof area is covered with vegetation (Rosenzweig et al., 2006).
In Venice, the field observation and simulations results showed that the tem-
perature of a green permeable surface could be 4C lower than the existing
paved roof (Peron et al., 2015). It was also estimated that the urban heat
island effect can be reduced by 12 degrees Celsius if 6% of Toronto was
covered with green vegetation (Peak, 2004). Another report on the
Mediterranean region shows that 10%14% of the electrical energy con-
sumed in cooling residential buildings can be saved by green roofs (Zinzi
and Agnoli, 2012). Green roof performance in reducing the urban heat island
effect varies in different locations, due to the conditions in the surrounding
environment, and changes in building density.
Increment of Urban Biodiversity
Green roofs can help to increase local biodiversity by providing habitats for
different animal species such as birds and insects within a city. A study
conducted in Switzerland found that 79 beetles and 40 spider species were
supported by a single green roof, of which 20 species were endangered
(Brenneisen, 2006). Another study conducted in England on green roofs
which mimic conditions found in derelict sites discovered that these sites are
favored by black redstart, a rare species of bird in the United Kingdom
(Grant and Lane, 2006).
However, creation of a habitat for animals is treated only as a bonus
compared with other quantifiable benefits. It is not easy to quantify the
increase in biodiversity and estimate the corresponding costs and benefits
using a common methodology. While it is difficult to directly quantify the
economic benefits of habitat increase due to green roofs, the resulting envi-
ronmental benefits may be translatable to economic terms based on environ-
mental priorities.
LIFE CYCLE COST OF GREEN ROOFS
Initial Cost
There is a significant price variation among green roofs due to factors such
as type and size, locations of green roofs, and country. The current cost in
British Columbia, Canada for a standard extensive green roof varies from
$130 to $165 m
2
, and the cost of a standard intensive green roof starts from
Economic Benefits and Costs of Green Roofs Chapter | 4.5 311
$540 m
2
(Bianchini and Hewage, 2011). Many factors such as labor and
equipment costs affect the installation price. In Singapore, a green roof price
ranges from $40 to $65 m
2
depending on the type of green roof and struc-
ture of the foundation (Wong et al., 2003). In China, the average price of a
green roof investigated from three provinces is between $48 and $76 m
2
(Jia and Wang, 2011; Liu and Hong, 2012). In a mature market like
Germany, the average green roof costs range from $15 to $45 m
2
. The
lower green roof prices in Germany are a result of ongoing research and
development as well as market penetration spanning two decades. In newer
markets, no economies of scale exist and competition is scarce. Labor is also
more expensive because of the lack of experience and the tendency to use
custom design systems. One way to reduce the initial cost of green roofs is
to adopt the low-cost techniques developed by mature markets. The cost of
green roof generally decreases by 33%50% once the industry has estab-
lished itself (Toronto and Region Conservation, 2007).
Operation and Maintenance (O&M) Cost
Economic and environmental benefits of green roofs rely on their perfor-
mance. Therefore, O&M of vegetative roofs are critical in securing their pos-
itive impacts. The maintenance cost also depends on the size of green roofs,
the characteristics of the building, the complexity of the green roof system,
the type of vegetation, as well as the market O&M price. It is estimated that
annual O&M cost of green roofs in the United States is between $0.7 and
$13.5 m
2
(Bianchini and Hewage, 2012).
Disposal Cost
There are different disposal options for green roofs at the end of life.
Materials can be landfilled, reused, or recycled. Water retention layer, drain-
age layer, and root barrier layers of green roof can be recycled again at the
end of the lifespan. However, many cities do not have the necessary facilities
for the recycling process. Landfill costs depend on many factors such as
technology, location, size of the facility, and available landfill capacity in a
municipality.
A study indicated that the operations and maintenance cost in landfilling
is on average $56 per ton waste disposed without considering the energy
recovery option (Chang and Wang, 1995). Another report compiled in
Europe did a complete analysis on the green roof disposal cost, including
inert material landfill, sanitary landfill, and incineration with energy recov-
ery. The disposal cost for an entire green roof is estimated at $1120 ton
1
(h784 ton
1
)(Peri et al., 2012). Bianchini and Hewage (2012) illustrated
that the cost to dispose green roof materials is in the range between $0.03
and $0.2 m
2
.
312 SECTION | IV Nature Based Strategies: Social, Economic and Environmental
GREEN ROOF COST BENEFIT ASSESSMENT
Net Present Value and Payback Period
In order to assess the total benefits and costs of green roof, the values
need to be converted into a net present value (NPV) by the means of dis-
counting. The lifespan of a green roof has been estimated as about 40
years minimum and 55 years maximum (Mahdiyar et al., 2016). In this
analysis, 40 years is used to conduct the assessment. Based on the study
from Gollier and Weitzman (2010), 3% of the discount factor was applied
to this analysis. Based on the benefits and costs of green roofs introduced
above, Table 1 summarized all the economic inputs for the analysis and
NPVs as output.
There is a wide range in terms of the values in Table 1, especially the
aesthetic benefits and stormwater runoff reduction benefits, and the life-
cycle costs. One of the reasons is due to the different systems of green
roofs. For example, extensive green roofs have shallow soil roofs with
simple growing plants, and are usually not accessible. Therefore they have
a lower lifecycle cost.
On the other hand, intensive green roofs are similar to a ground level
garden with a deep growing medium and artificial irrigation (Kosareo and
Ries, 2007). Therefore, the initial cost and O&M cost are higher. At the
same time, intensive green roofs have higher benefits in stormwater run-
off deduction due to its deep growing medium, and better aesthetic values
because it acts like a garden. Another reason is the cost and technique
variances between different markets. In the mature market like Germany,
the costs are much lower than the new markets in Asia and North
America, and the benefits generated from green roofs are more than the
new markets because of its mature techniques and great popularity. Some
other reasons are sizes of green roofs, weather conditions, and building
features etc.
As shown in Table 1, the total NPV of individual benefits in 40 years is
between $135.9 and $195.8 m
2
, and the total NPV of public benefits in 40
years is between $478.7 and $751.7 m
2
. Based on the result, it is obvious
that the public benefits are over three times greater than the individual bene-
fits, even though two of the public benefits are not counted in the calculation
due to the unavailable data.
If the total NPV of lifecycle costs for green roofs in 40 years is close to
$42.3/m
2
, which is at the lower side of the range ($42.3978.8 m
2
), it will
only take 13 years of the individual benefits to balance the cost of green
roofs. If the public benefits are considered, the payback period will be
reduced to 3 years. If the total NPV of lifecycle cost for green roofs in
40 years is close to $978.8 m
2
, this cost could still be paid back in its life-
time by the individual benefits and public benefits together.
Economic Benefits and Costs of Green Roofs Chapter | 4.5 313
Scale of Implementation
As shown in Table 1, the values created by the mitigation of urban heat
island effect and increment of urban diversity are not available in this analy-
sis, because the value would be very small if only one or a few green roofs
were installed. However, the benefits of green roof will increase
TABLE 1 Economic Data Input and NPV Output ($ m
2
) for the Cost
Benefit Assessment
Value Time
Frame
(Year)
NPV
($ m
2
)
Economic
Factor
Lifespan (year) \ 40 \
Discount rate (%) 3 \ \
Individual
Benefits
($ m
2
)
Reduction of energy 0.40.9 Annual 15.735
Use in heating and
cooling
Membrane longevity 160 At year 20 88.6
Acoustic insulation 29 One time 29
Aesthetic benefits 2.643.2 One time 2.643.2
LEED certification
bonus
n/a n/a n/a
Total NPV 135.9195.8
Public Benefits
($ m
2
)
Reduction in
stormwater runoff
15 - 28 Annual 477.5750.6
Improvement of air
quality
0.03 Annual 1.18
Mitigation of urban
heat island effect
n/a n/a n/a
Increment of urban
diversity
n/a n/a n/a
Total NPV 478.7751.7
Lifecycle Costs
($ m
2
)
Initial cost 15540 One time 15540
Operation and
maintenance cost
0.713.5 Annual 27.3438.7
Disposal cost 0.030.2 At year 40 0.010.06
Total NPV 42.3978.8
314 SECTION | IV Nature Based Strategies: Social, Economic and Environmental
tremendously if implemented at a larger scale. Intangible benefits such as
aesthetic appeal of green roofs and increased urban biodiversity can be
gained with large scale of implementation (Niu et al., 2010; Nurmi et al.,
2013) . The costs of green roofs will also be reduced with a higher imple-
mentation rate. Large scale of implementation would also reduce the volume
of stormwater entering local waterways, which will lead to lower water tem-
peratures, less in-stream scouring, and better water quality (Spengen, 2010).
Green Roof Policy Initiatives
Based on the analysis above, the public benefits of green roofs are over three
time larger than the private benefits. Therefore, municipal authorities should
play a key role in promoting green roofs in urban areas and residential neigh-
borhoods through policy and regulatory measures.
In Toronto, Green roofs are required on all new institutional, commercial,
and multiunit residential developments. The incentive offered for green roof
is $75 m
2
up to an upper limit of $100,000 (City of Toronto, 2016). In New
York, green roof tax abatement is implemented, so that each square foot of
green roof can get a rebate of $5.23, up to $200,000 per project (NYC,
2014). In Singapore, the National Parks Board aims to increase greenery pro-
vision by funding up to 50% of the installation cost of rooftop greenery
(National Parks, 2011). In Tokyo, it is mandatory for a new building to cover
25% of roof with greenery (Growing Green Guide, 2013).
In Munich, all building roofs with a surface area larger than 100 m
2
should be landscaped. This policy was implemented around 20 years ago,
and it makes the green roof a recognized construction standard in Munich
(IGRA, 2011). As a world leader in green roof development, Germany’s
experience shows that it is necessary to introduce a green roof policy rather
than rely solely on the goodwill of building owners (Ngan, 2004).
CONCLUSION
Green roofs have personal and social benefits. The cost benefit assessment
showed that the lifecycle costs of green roofs can be retrieved in most of the
markets around the world. The payback periods in the mature markets and
markets with average initial costs are shorter than the lifespan of green roofs.
With a larger implementation scale, the social benefits of green roofs will be
increased tremendously. Governments should play a key role in promoting
the green roof construction by providing incentives to transfer the social ben-
efits into private investors, such as tax abatement, direct cash rebate, low
interest loans, etc. These incentives will also expand the public benefits, and
lower the lifecycle cost of green roofs.
Economic Benefits and Costs of Green Roofs Chapter | 4.5 315
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318 SECTION | IV Nature Based Strategies: Social, Economic and Environmental
... There are two different perspectives in financial-feasibility analyses of GR installation: 1) private perspective, 2) social perspective, where the economic feasibility of GR adoption has been investigated in different climates by the prediction of net present value (NPV) and payback period (PBP) (Ávila-Hernández et al., 2020;Bianchini and Hewage, 2012;Mahdiyar et al., 2016;Teotónio et al., 2020Teotónio et al., , 2018Ziogou et al., 2018). In the study conducted by Feng and Hewage (2018), the cost-benefit assessment showed that lifecycle costs of GRs can be retrieved in most of the markets around the world. It was concluded that NPV for GR installation is always positive and this value of GR social benefits could be much more than private ones, especially when it is used in a large scale. ...
... The costs consist of disposal charges and increased air pollution through the production of plastic layers of GRs (Peri et al., 2012). The social benefits are effective when GRs are installed on a large scale in urban areas (Feng and Hewage, 2018;Versini et al., 2020), while their effect could be either short-or long-term. According to Shafique et al. (2020b), the reduction in air pollution, UHI effect, and energy consumption are short-term effects, while the decrease in greenhouse gas emissions is considered as a long-term effect. ...
... It has been proved that initial cost (IC) and maintenance cost (MC) are among the most critical issues in GR installation (Berto et al., 2018;Besir and Cuce, 2018;Feng and Hewage, 2014;Gargari et al., 2016), and significantly affect the cost-related analysis. Various values are reported by the researchers as the IC and MC of IGR and EGR, based on the location of the research (e.g., (Berardi, 2016;Feng and Hewage, 2018)). Mahdiyar et al. (2016) conducted a study in Kuala Lumpur and investigated the IC and MC for both types of GRs. ...
Article
Green roofs (GRs) have several private, environmental, and social benefits, though financial issues have been considered a major barrier to its widespread use. The lack of knowledge and information regarding the value and applicability of each such benefit has resulted in limited adoption of GRs in Malaysia. Hence, the aim of this research is to analyse the financial feasibility of GR installation, considering social and private perspectives (where the applicability of benefits varies across various scenarios). To do that, the applicable short- and long-term costs and benefits of GRs were identified through reviewing the literature. Then, the variables’ values were investigated and calculated using Monte Carlo simulation. GRs’ net present value (NPV) and discounted payback period (DPBP) were analysed in different private scenarios to derive its financial feasibility out in Kuala Lumpur. Additionally, projected social benefits were analysed to indicate the government’s financial benefit from GR adoption. The results showed that NPV for the private sector could be up to $1072.44m2 and $735.11m2, while it is most likely around $390.78m2 and $258m2 for intensive GR (IGR) and extensive GR (EGR), respectively. Most probably, the DPBP would be between one and nine years and one and six years for IGR and EGR, respectively. Additionally, considering the social benefits of GR, IGR has the potential to offer up to $314m2; the amount is much lower for EGR at $55m2. Moreover, it was found that energy saving is the most influential variable affecting NPV in private and social perspectives. Finally, it was concluded that GR installation could be financially feasible if all private benefits are applicable. Since GR has social financial benefits, the initial costs could be partially covered by the government as an incentive for GR installers.
... However, CBA is considered as one of "the most widely applied tools for economic analysis" (Balanay and Halog, 2019) and it is used to economically evaluate NBS. For example, Feng and Hewage (2018) used CBA to assess the payback period of green roofs in different markets, considering life cycle costs, public and individual benefits. CBA considering public and private costs and benefits was also deployed by Reddy et al. (2015) to assess water shortages risk of alternative scenarios (including NBS). ...
Article
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Water has been pushed into a linear model, which is increasingly acknowledged of causing cumulative emissions of pollutants, waste stocks, and impacting on the irreversible deterioration of water and other resources. Moving towards a circular model in the water sector, the configuration of future water infrastructure changes through the integration of grey and green infrastructure, forming Nature-based Solutions (NBS) as an integral component that connects human-managed to nature-managed water systems. In this study, a thorough appraisal of the latest literature is conducted, providing an overview of the existing tools, methodologies and indicators that have been used to assess NBS for water management, as well as complete water systems considering the need of assessing both anthropogenic and natural elements. Furthermore, facilitators and barriers with respect to existing policies and regulations on NBS and circularity have been identified. The study concludes that the co-benefits of NBS for water management are not adequately assessed. A holistic methodology assessing complete water systems from a circularity perspective is still needed integrating existing tools (i.e. hydro-biogeochemical models), methods (i.e. MFA-based and LCA) and incorporating existing and/or newly-developed indicators.
... Their presence has a positive influence on people's quality of life and well-being [45]. The benefits also derive from the presence of animal and plant species (biodiversity) [46] that live in these green spaces and the possibility of being able to observe them closely. In particular, green roofs are appreciated because they are: green spaces located at high altitude with panoramic views of the surrounding urban environment; -spaces where plants and plant species are cultivated, even edible plants, and it is possible to observe animal species (e.g., birds); -social gathering and meeting spaces (especially in the presence of cafes, restaurants, etc.). ...
Article
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A wide diffusion of green envelopes in cities can be an opportunity to improve urban environment conditions and reduce negative effects of climate change. The green roof system is a widespread solution adopted all over the world due to the relative simplicity of installation and the large private and social benefits provided. Despite this, some factors hinder the diffusion of the green roof system, not only economic factors (due to the higher installation costs compare to a traditional roof solution), but also technical factors connected to lack of knowledge. The present paper investigates the factors influencing designers in the choice of a building roof systems, comparing a traditional solution and a greening system. The involvement of architects, engineers, and researchers allows the selection of the most important factors. Results of the study identifies their priority, and through a sustainability-based multicriteria analysis, the role played by each one in the decision process. This approach provides interesting hints to identify effective strategies to support a wider diffusion of greening systems for urban resilience.
... Intensive roofs are characterized by their greater weight (200-500 kg/m 2 ), high capital cost ($540/m 2 ), high irrigation requirements, fertigation, and maintenance requirement. On the other hand, extensive green roofs are often not accessible, consisting of low-growing plants such as succulents, herbs, and grasses (Figure 1b), and are characterized by low weights (60-150 kg/m 2 ), low capital costs (130-165 $/m 2 ), low plant diversify, and minimal irrigation, nutrient, and maintenance requirement [24,25]. A relative comparison of intensive and extensive green roofs is shown in Table 1. ...
Article
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Buildings are one of the biggest consumers of fossil fuels, and thus, contribute largely to greenhouse gas emissions. As a result, a large number of studies have been conducted and innovative ideas or green solutions have been invented, adopted, and implemented across the globe. These solutions are often contextual and heavily dependent on local environmental and socioeconomic factors. Green roofs are such an example. Green roofs (both intensive and extensive) for buildings have been successfully adopted in many countries around the world. Bangladesh, a developing country that can benefit from green roofs, seems to remain in complete darkness regarding its potential. The objective of this study is to identify the reasons why green roofs have not been widely implemented in Bangladesh, especially in the capital Dhaka, even though, theoretically, the climatic conditions of this country favor this technology. This study focuses on the perception of the construction industry to comprehend the possible obstacles they are facing towards using green roofs in their designs. A questionnaire study was conducted among architects, engineers, construction managers, contractors, and owners who are at different levels of experience in their respective fields. The results indicate a gap in knowledge and misconceptions, which are major hindrances to the implementation of green roofs.
Article
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Green roofs, which have various economic, environmental and social effects, have been acknowledged as an alternative green space in urban areas. This study aims to investigate the economic feasibility of green roof projects by conducting a benefit–cost analysis on the case of Jung-gu, Seoul. The analysis estimates and compares five different scenarios applied in the study area with a 20-year operation period in all cases. This set of scenarios aims to compare the most idealistic situation with more achievable and realistic situations, to provide policy implications for green roof initiative projects in Seoul. The analysis consists of estimating six cost items and eight benefit items. Among the benefit items, two non-marketable elements are estimated by the contingent valuation method. The scenario with 100% application of a green roof, has benefits exceeding the costs with a benefit–cost ratio of 1.174. However, the other scenarios with certain prerequisites have a benefit–cost ratio that is very close, but still smaller than 1. Therefore, it is possible to claim that green roof initiative projects are economically viable under specific conditions. However, there are many restrictions to engaging in green roof constructions for entire building rooftops.
Article
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Greenery on buildings is being consolidated as an interesting way to improve the quality of life in urban environments. Among the benefits that are associated with greenery systems for buildings, such as energy savings, biodiversity support, and storm-water control, there is also noise attenuation. Despite the fact that green walls are one of the most promising building greenery systems, few studies of their sound insulation potential have been conducted. In addition, there are different types of green walls; therefore, available data for this purpose are not only sparse but also scattered. To gather knowledge about the contribution of vertical greenery systems to noise reduction, especially a modular-based green wall, two different standardised laboratory tests were conducted. The main results were a weighted sound reduction index (Rw) of 15 dB and a weighted sound absorption coefficient (α) of 0.40. It could be concluded that green walls have significant potential as a sound insulation tool for buildings but that some design adjustments should be performed, such as improving the efficiency of sealing the joints between the modular pieces.
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Green roofs offer various kinds of ecosystem services that are often scarce especially urban areas. These services accrue benefits to urban dwellers. However, ecosystem services do not generally have a market price, thus we had to use ecosystem valuation methods to estimate the benefits. Based on the valuation, the most significant benefits were: an increased lifespan of the roof, energy savings due to increased isolation and cooling, improved storm-water management, better air-quality and sound insulation especially in the air craft noise zones. In addition, other potentially significant benefits include aesthetic benefits, health benefits and improved biodiversity. Only a share of the green roof benefits accrues to the owner of the property while other benefits are distributed among the population of a larger area. We found that private benefits are in most cases not high enough to justify the expensive investment of a green roof instalment since the costs are incurred solely by the private decision makers (e.g. developers, real estate buyers). The cost-benefit calculations hint that with a higher rate of implementation and realization of public benefits, the green roofs would be a good investment. However, because the private benefits are not high enough to justify a green-roof installation for a private decision-maker at the current cost level, the rate of implementation can be expected to stay low without corrective policy instruments.
Article
In Italy, as in the rest of Europe, serious land degradation processes are occurring, mostly due to rural abandonment, urbanization and infrastructure development. In particular Veneto, the region around Venice, has undergone considerable land use and land cover change in the last decades. This work integrates field observations and numerical simulations to study the urban heat island (UHI) effect in the mainland part of Venice. The numerical study was performed using ENVI-met, an environment and micro-climatic simulation tool. Different mitigation scenarios are evaluated in a case study area. The study aims to explore the factors that contribute to urban heat island development proposing practical, feasible and specific solutions for mitigating their effects. The focus of the analysis is, in particular, on the use of permeable surfaces vegetative soil or grassed parking instead of conventional asphalt or cement pavement as soil compensation mechanisms for soil loss. The replacement of traditional roofs with cool or green ones is also considered.
Article
Low-energy pollutant removal strategies are now being sought for water sensitive urban design. This paper describes investigations into the water quality and quantity of sixteen, low-maintenance and unfertilized intensive and extensive green roof beds. The factors of Slope (1° and 25°), Depth (100 mm and 300 mm), Growing media (type A, type B and type C) and Species (P1, P2 and P3) were randomized according to a split-split plot design. This consisted of twelve vegetated green roof beds and four non-vegetated beds as controls. Stormwater runoff was collected from drainage points that were installed in each area. Samples of run-off were collected for five rainfall events and analysed for water retention capacity and the water quality parameters of NO2, NO3, NH4, PO4, pH, EC, TDS, Turbidity, Na, Ca, Mg and K. The results indicated significant differences in terms of stormwater water quality and quantity between the outflows of vegetated and non-vegetated systems. The water retention was between 51% and 96% and this range was attributed to the green roof configurations in the experiment. Comparing the quality of rainfall as inflow, and the quality of runoff from the systems showed that green roofs generally acted as a source of pollutants in this study. In the vegetated beds, the intensive green roofs performed better than the extensive beds with regard to outflow quality while in the non-vegetated beds, the extensive beds performed better than intensive systems. This highlights the importance of vegetation in improving water retention capacity as well as the role of vegetation in enhancing pollutant removal in green roof systems. In addition growing media with less organic matter had better water quality performance. Comparison of these results with national and international standards for water reuse confirmed that the green roof outflow was suitable for non-potable uses such as landscape irrigation and toilet flushing.
Conference Paper
In this paper cost-effectiveness assessment techniques were used to evaluate the economic impacts of the widespread emerging of new buildings being aim for green roof projects in a life-cycle scale on three typical rural building stocks. Results show contrast to traditional one the building with green roof bring out more economic benefits by providing a outstanding medium for building energy consumption decreasing, vegetable cultivating to its owner and that the economic benefits of green roof in its life-cycle scale are much bigger than the additional construction investment cost on converting traditional one to green roof building in every research region. After quantitative analysis of the cost-benefits of green roof project in rural region the currently hindering factors of popularizing the project are analyzed and countermeasures are proposed to guide green roof popularizing policy path.
Article
Green roofs have been used as an environmentally friendly product for many centuries and considered as a sustainable construction practice. Economic and environmental benefits of green roofs are already proven by many researchers. However, a lifecycle net benefit-cost analysis, with the social dimension, is still missing. Sustainable development requires quantitative estimates of the costs and benefits of current green technologies to encourage their use. This paper is based on an extensive literature review in multiple fields and reasonable assumptions for unavailable data. The Net Present Value (NPV) per unit of area of a green roof was assessed by considering the social-cost benefits that green roofs generate over their lifecycle. Two main types of green roofs – i.e. extensive and intensive – were analyzed. Additionally, an experimental extensive green roof, which replaced roof layers with construction and demolition waste (C&D), was assessed. A probabilistic analysis was performed to estimate the personal and social NPV and payback period of green roofs. Additionally, a sensitivity analysis was also conducted. The analysis demonstrated that green roofs are short-term investments in terms of net returns. In general, installing green roofs is a low risk investment. Furthermore, the probability of profits out of this technology is much higher than the potential financial losses. It is evident that the inclusion of social costs and benefits of green roofs improves their value.
Article
Green roofs can be classified as intensive and extensive roofs based on their purpose and characteristics. Green roofs are built with different layers and variable thicknesses depending on the roof type and/or weather conditions. Basic layers, from bottom to top, of green roof systems usually consists of a root barrier, drainage, filter, growing medium, and vegetation layer. There are many environmental and operational benefits of vegetated roofs. New technology enabled the use of low density polyethylene and polypropylene (polymers) materials with reduced weight on green roofs. This paper evaluates the environmental benefits of green roofs by comparing emissions of NO2, SO2, O3 and PM10 in green roof material manufacturing process, such as polymers, with the green roof’s pollution removal capacity. The analysis demonstrated that green roofs are sustainable products in long-term basis. In general, air pollution due to the polymer production process can be balanced by green roofs in 13–32 years. However, the manufacturing process of low density polyethylene and polypropylene has many other negative impacts to the environment than air pollution. It was evident that the current green roof materials needed to be replaced by more environmentally friendly and sustainable products.