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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
... The significant emissions from hospitals increase the risk of climate change related health issues and contributes to the general degradation of the environment caused by climate change (Costanza et al., 2014;Eckelman and Sherman, 2016;Toli and Murtagh, 2020). Urban hospitals provide ideal space for supporting green roofs because of: the ability for hospitals to mitigate environmental concerns affecting public health through ecosystem services provided by the green roofs; the hospitals' goals to improve the health and well being of the community; and the relatively high proportion that have large, flat, unoccupied roof space that is commonly unutilized (Ulrich, 2002;Coutts and Hahn, 2015;Feng and Hewage, 2018). ...
... Green roofs in urban areas, on the other hand, have been documented to reduce a roof 's surface temperature as well as the rate of solar radiation transferred, in addition to cooling the air through evapotranspiration. Collectively, these actions reduce the UHI effect (Rakhshandehroo et al., 2015;Bevilacqua et al., 2017;Feng and Hewage, 2018;Cai et al., 2019). The naturally occurring insulating properties of plants and vegetation create a barrier between the sun and the building, limiting the amount of solar radiation that is absorbed and released as wasted energy (Shafique et al., 2018). ...
... The naturally occurring insulating properties of plants and vegetation create a barrier between the sun and the building, limiting the amount of solar radiation that is absorbed and released as wasted energy (Shafique et al., 2018). The rate of solar radiation transferred onto building roofs with green roofs ranges from 6-30% in the summer and 10-80% in the winter based on the density and type of plants and the amount of evapotranspiration occurring (Rakhshandehroo et al., 2015;Feng and Hewage, 2018). The reduced solar radiation transferred, in addition to the cooling effects from evapotranspiration, result in green roofs having surface temperatures less than half that of a traditional roof (Bevilacqua et al., 2017). ...
Article
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If worldwide healthcare was a country, it would be the fifth largest emitter of greenhouse gases on the planet. The increase in global temperatures, combined with the negative impacts of urbanization, has made it more important than ever to introduce green spaces where possible. With climate change worsening, human health, both physically and mentally is on decline, making the effects of climate change especially pressing to the stability of healthcare systems. In order to mitigate the lasting impacts of climate change on healthcare facilities, a holistic solution is needed. Access to green space in hospitals has been shown to reduce emotional distress, improve mental health, increase socialization and community connection, increase physical activity, decrease cardiovascular and respiratory diseases, decrease pain management needs and hospital stay lengths and increase both patients' and staffs' overall satisfaction at the facility. Beyond benefiting those interacting with the hospital, green roofs have the ability to reduce the urban heat island effect, improve stormwater mitigation, increase biodiversity, and absorb toxins and pollutants through air filtration. Additionally, green roofs can offer lower maintenance costs and higher energy savings than traditional roofs, and improve patient satisfaction, which can result in future funding opportunities. However, the upfront and upkeep costs of installing a green roof can vary and must be considered before implementation. In this review, we explore the symbiotic relationship between urban green roofs and hospital/patient wellness through the lens of sustainability, which includes environmental, societal, and economic impacts. We review scientific journal articles investigating benefits of green space and green roofs and highlight examples of green roofs on hospitals in the United States; together, these approaches display the environmental, societal, and economic benefits of green roofs installed on healthcare facilities. This review offers insight to hospitals, decision makers, and government systems on the importance of green roofs in urban areas and how these infrastructures can support the economic growth of the institute. Using our framework, decision makers and planners for urban hospitals can evaluate how the addition of green roofs to their healthcare facilities can contribute to increased environmental resiliency, community health, and patient satisfaction.
... The analyses of green roof life cycles, however, face challenges that on occasions limit their ability to provide a clear overview of their functions and impacts or inhibit the comparison of their results and the drawing of common conclusions. These challenges include the multi-disciplinary nature of green roofs' technology and industry, the frequent lack of local research and data (Shafique et al., 2018), the variance of their properties and performance based on region-sensitive factors such as local climate, vegetation characteristics and construction practices (Theodosiou, 2009), material and labour costs (Ulubeyli et al., 2017), market maturity (Feng and Hewage, 2018) and others. In addition, many green roofs benefits and challenges (air quality improvements, noise reduction, eutrophication potential, recreational benefits) are frequently hard to evaluate qualitatively and quantitatively both under an environmental (Shafique et al., 2018) or economic lens . ...
... This phenomenon does not apply only to this kind of analysis but has been recorded to influence the effectiveness of other types of economic models too (Kliestik et al., 2018) rendering their adjustment to local conditions necessary (Kovacova et al., 2019). , green roof and individual layer types (Shafique et al., 2020a), market and industry maturity (Feng and Hewage, 2018), material and labour costs, discount rates (Ulubeyli et al., 2017), property values, tax policies, building characteristics, installation costs, energy consumption costs, have a significant effect on the results. In addition, between studies, the variety of methods used, the differentiation in costs and benefits included, the challenges in quantifying and monetizing numerous green roof impacts and functions, all hinder the ability to draw definitive conclusions about their economic viability or compare research outcomes . ...
Article
Green roofs constitute a prominent urban green infrastructure solution and are considered to be able to enhance urban sustainability and resilience. Existing literature, however, lacks a holistic evaluation of their life cycle impacts. In this study, a comparative environmental and economic life cycle analysis between green and flat roofs under Mediterranean climate conditions was conducted, examining all green roof types (extensive, semi-intensive, intensive), two types of drainage layer (granular and synthetic) for each one, all green roof layer materials, life cycle stages (production of materials, use and maintenance, disposal) and their quantifiable costs and benefits, aiming to address this research gap. Dynamic whole-building energy demand simulations were also conducted in its context, which additionally investigated the effect of various factors on green roofs' energy saving potential. Thermally insulated green roofs provided a small improvement in the energy consumption for heating and cooling (up to 8.30% and 3.50% respectively) but significant reductions in total life cycle energy consumption (8-31%), CO 2 emissions (24-32%) and waste production (15-60%) rendering them a cleaner environmental option compared to flat roofs. However, they also produced a very important increase in total life cycle water consumption (279-835%). The extensive green roof types were the ones to perform better in all these indexes. They were also the only type to constitute a better economic choice than a flat roof for the private owner in a low discount rate (0.25%) scenario, both with or without public benefits. As this study shows, the green roofs' potential is not limited only to the improvement of the buildings' energy efficiency, as numerous studies in the field of energy efficiency highlight, but compared to flat roofs, expand to reduce the embodied energy, greenhouse gas emissions and material waste. By means of environmental footprint, they are superior to flat roofs when only energy and emissions are considered, while in regions where water availability is a key environmental factor, this superiority is in question, together with their economic feasibility in countries where this technology is not financially supported.
... Incentives for the wider application of green roofs are required for cities in India that face high temperatures during summers. Nature-based solution can also help build resource efficiency by reducing the urban heat island effect and problems related to urban flooding (Feng & Hewage, 2018). The market for naturebased solutions such as green roofs is low even though there is evidence to show that green roofs reduce the energy used for cooling (Bianchini & Hewage, 2012). ...
Article
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Energy and waste management sectors are considered important for the country’s progress towards adopting sustainable consumption and production (SCP) practices and achieving Sustainable Development Goals. However, the rapid pace of urbanization, energy-intensive growth approaches, and generation of large quantities of waste have led to severe environmental degradation of cities in India. While the government has taken several initiatives for increasing resource efficiency, limited research has been done in an Indian context to explore the policy and institutional factors. The paper focuses on challenges relating to policy enablers within the energy management in buildings and construction and demolition waste sectors; 28 semi-structured interviews were conducted with stakeholders associated with both these sectors. The findings indicate that though India has been integrating climate change measures into its national policies and enhancing the domestic market’s readiness for a circular economy, successful implementation of policy framework(s) urgently requires lifestyle and behavioural changes in the society. The study further identified the role of key stakeholders including government, businesses, and consumers, for transition to a low-carbon economy for both these sectors. This paper presents a bottom-up approach to understand the changes required in the enabling environment for the uptake of SCP practices that can be adapted by other emerging economies in the Asia Pacific region for building resource efficiency. The importance of soft factors relating to institutional capacities and governance structure is raised by the analysis in this paper.
... Thus, these costs were: 8%/year of construction costs for bioretention (Houle et al., 2013;Chui et al., 2016;Wang, Zhang, Lou et al., 2019), 4%/year of construction costs for permeable pavements (Houle et al., 2013;Chui et al., 2016; and R$ 29.75/m 2 .year for green roofs (Acks, 2006;Bianchini & Hewage, 2012;Feng & Hewage, 2018). ...
Article
High rates of soil imperviousness, intensified by urbanization, have been contributing strongly to the occurrence of floods all over the world. To mitigate these impacts, Low Impact Development (LID) techniques seek to preserve the hydrology of urban catchments closer to pre-development conditions by using distributed stormwater control systems. Nevertheless, the application of these techniques is associated with a variety of challenges, including the design of the LID controls, due to the significant number of variables involved and the need to attend to multiple objectives simultaneously. In this context, the application of hydrologic simulation models integrated with optimization techniques has been recently explored as an alternative to assist in planning LID scenarios. This work aims to verify the applicability of an adaptation of the Genetic Algorithm NSGA-II, together with the hydrologic model SWMM, to assist the optimal design of a LID scenario seeking to reduce the stormwater runoff and the total costs on different return periods. This scenario has considered the combined implementation of permeable pavements, green roofs and bioretention cells. The results showed that the model was capable of finding a great variety of optimal solutions on various levels of runoff reduction, at different costs, for all return periods considered. Regarding the applicability of the optimization model as a LID design method, some limitations were found related to practical applications and possible oversizing of the subjacent layers of the LIDs. Therefore, suggestions on how to improve the model have been made to solve the identified problems.
... When it comes to the opportunities offered by GR projects, they are known for their contribution to reducing the adverse impacts of the construction industry on the environment such as urban heat island and greenhouse gas and CO 2 emission. However, these opportunities are offered if GRs are installed on a large scale (Feng & Hewage, 2018;Versini et al., 2020). In addition, some opportunities might be applicable to GRs designed for specific GRs. ...
Article
A green roof (GR) provides numerous social, environmental, and personal benefits through its lifespan, while exploiting these benefits is associated with several uncertainties. Since these risks to GR adoption have not yet been investigated and analyzed comprehensively, this research is aimed at developing an original risk assessment model to ensure the objectives of GR adoption are fully achieved. To this end, two novel approaches were employed, namely Monte Carlo-DEMATEL and fuzzy parsimonious analytic network process to determine the inner dependencies among the risk factors and rank them based on their relationships and importance, respectively. The findings showed that “irregular maintenance” and occurrence of “fire” are the most influential threats, while “flash flood reduction” and “achieving green building certificate award” are among the most influential opportunities. Moreover, it was shown that although “tax abatement” and “monetary loss” are the most important opportunity and threat, respectively, the ranking order of risk factors varies among an intensive GR and an extensive GR. Finally, it was concluded that with such analyses, the decision-makers have clear insights on the most influential positive and negative risks for managing purposes. The novel methods used in this research can be replicated to achieve more accurate and efficient results.
... Concerning the economic aspects, previous studies [69,70] performed at the single building level have demonstrated that, although GRs are often not a cost-effective solution on private single houses, they become economically more competitive on a larger scale, especially when aesthetic and social benefits (such as UHI attenuation, greenhouse gases emissions and storm-water runoff reduction) are also taken into account. ...
Article
The effects of climate change on the built environment represents an important research challenge. Today, green roofs (GRs) represent a viable solution for enhancing energy and urban resilience in the face of climate change, as they can have a positive impact on the building's indoor thermal comfort and energy demand, as well as inducing various environmental benefits (easing urban heat island effects, improving the management of runoff water, reducing air pollution, etc.). Thus, it is important to be able to assess their effectiveness, both today and under future climate conditions, in order to evaluate whether they can also provide a valid long-term solution. In this paper, a simulation approach is proposed to evaluate the energy and indoor-comfort efficacy of GRs installed on a cluster of buildings with respect to climate change and demographic growth. To illustrate the proposed methodology, it has been applied to two European urban environments characterized by very different climatic conditions (Esch-sur-Alzette in Luxembourg and Palermo in Italy) considering their behaviour over a period of 60 years (2020, 2050, 2080). Results showed that, with respect to standard existing roofs (i.e., without the presence of green coverage), and considering the rising temperatures due to climate change, during cooling seasons GRs enabled significant energy savings (ranging from 20% to 50% for Esch-sur-Alzette and from 3% to 15% for Palermo), improvement of the indoor comfort (reduction of the average predicted mean votes − PMVs) and attenuation of the ceiling temperatures (2–5 °C for both contexts) of the buildings' top floors.
... The CBA method is one of "the most widely applied tools for economic analysis" (Balanay and Halog, 2019). In terms of NBS, CBA has been used in assessing nature-based solutions; for example, Feng and Hewage (2018) applied CBA based on life cycle costs, individual and public benefits to assess the payback period of green roofs in different markets. Calculation of Payback period and net present value revealed that there are individual and social advantages to green roofs. ...
Article
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The transition from the current linear model of abstraction, use and discharge of water into recycle-reuse under the circular economy (CE) principles is momentous. An analysis of recent literature about the economic impact of linear to circular (L2C) transition is made. The review investigates the economic implications (i.e. cost-benefit) of deployment of enabling technologies, tools and methodologies within the circular water systems. The study is enhanced by presenting the results of our investigation into the policy impact (push-barriers) of L2C transition. As the vehicle for the L2C transition, Nature-Based Solutions (NBS) and its economic and policy implications is discussed. A framework is proposed for the monetary assessment of the costs of investment in NBS technologies, infrastructure and education against the environmental and socio-economic benefits within the policy frameworks. This framework may build the early foundation for bridging the gap that exists for a systematic and objective economic impact (cost-benefit) analysis of L2C transition in the Water sector. This framework will lead to a generic multi-parametric cost model of NBS for Circularity Water Systems.
Chapter
Green roofing is a nature-based solutionNature-Based Solutions (NBS) to urban environmental problems and an alternative for urban designers to provide additional spaces for outdoor activities and entertainment under the trend of urban open space reduction. However, several barriers hinder green roofing implementation, including lack of government policy, unsound technological development, high initial cost and long payback period, and individual unwillingness. Governmental policy is the most effective strategy for sustainable initiative implementation by overcoming their barriers. Therefore, this chapter aims to reveal policy and regulatoryRegulatory landscapes for green roofing. In particular, the analysis is conducted in China, a country undergoing rapid urbanisation and severe environmental, economic and social challenges in cities. In particular, this chapter presents an overall picture of policy and regulatoryRegulatory landscapes for green roofing in mainland China across the national, provincial, and city scalesCity-scale, considering mandatory and guiding terms. The analysis indicates that there is no specific national document for roof greeningRoof greening promotion. Nevertheless, in the central government's guide, opinion, notice, and technical standards and specifications, roof greeningRoof greening is advocated in other projects, such as environmental protectionEnvironmental protection, green buildingGreen building, sponge city, and urban landscaping. Roof greeningRoof greening is mostly mentioned for green space or landscape benefits, but other functions have not been particularly defined. Roof greeningRoof greening has been more clearly framed in province-level technical guideTechnical guide/specification, legislated regulations, governmental opinion, provincial plan, and economic support. The results indicate that the provincial policies and regulations are uneven in geographical distribution, mainly in the east part of mainland China. Technical guideTechnical guide/specification is the main approach to promoting green roofsGreen roof, followed by the legislated specification, governmental opinion, and provincial plan and economic support. However, among the 25 provinces that have suggested green roofGreen roof implementation, only ten provinces have clarified the specific requirements of intensive and extensive green roofsGreen roof. In addition, incentives for green roofGreen roof implementation have been analysed, indicating that urban greeningUrban greening conversion is the most common way to green roofing promotion at both province and city scalesCity-scale, followed by the fiscal subsidiesSubsidies and then awards. City-level incentives are more inspiring, sounder, and more comprehensive than province-level incentives. In addition, the results indicate that while the Urban GreeningUrban greening Ordinance exhibits a strong top-down impact on provincial legislated specifications, the policy and regulatoryRegulatory landscapes for green roofGreen roof implementation show a strong bottom-upBottom-up pattern from cities to provinces and then to mainland China. Overall, this chapter is of significance to the understanding of the policy and regulatoryRegulatory landscapes for green roofGreen roof implementation and provides a reference to the next-step reformReform of the current policy system.
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Urban greening is an effective mitigation option for climate change in urban areas. In this contribution, a European Union (EU)-wide assessment is presented to quantify the benefits of urban greening in terms of availability of green water, reduction of cooling costs and CO 2 sequestration from the atmosphere, for different climatic scenarios. Results show that greening of 35% of the EU’s urban surface (i.e. more than 26,000 km ² ) would avoid up to 55.8 Mtons year ⁻¹ CO 2 equivalent of greenhouse gas emissions, reducing energy demand for the cooling of buildings in summer by up to 92 TWh per year, with a net present value (NPV) of more than 364 billion Euro. It would also transpire about 10 km ³ year ⁻¹ of rain water, turning into “green” water about 17.5% of the “blue” water that is now urban runoff, helping reduce pollution of the receiving water bodies and urban flooding. The greening of urban surfaces would decrease their summer temperature by 2.5–6 °C, with a mitigation of the urban heat island effect estimated to have a NPV of 221 billion Euro over a period of 40 years. The monetized benefits cover less than half of the estimated costs of greening, having a NPV of 1323 billion Euro on the same period. Net of the monetized benefits, the cost of greening 26,000 km ² of urban surfaces in Europe is estimated around 60 Euro year ⁻¹ per European urban resident. The additional benefits of urban greening related to biodiversity, water quality, health, wellbeing and other aspects, although not monetized in this study, might be worth such extra cost. When this is the case, urban greening represents a multifunctional, no-regret, cost-effective solution.
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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.