This report has been developed in
response to the request for proposal on developing solution of an environmental
problem.
In this proposal, the
team identified that there is a severe need to mitigate the Urban Heat Island
(UHI) effect in Singapore. Neo (2018) claimed that the probability of excessive
heat or sudden and histrionic temperature increase is catastrophic and can
result in increased rates of health issues and mortality.
The team believes that the older
Housing Development Board (HDB) estates have a limited solution to mitigate the
UHI effect. In the best interest of reducing the UHI effect to the residents,
the team proposes a solution to retrofit the rooftop of Multi-Storey Carpark
(MSCP) with a green roof. Not only does the proposed solution mainly reduces
surface temperature, it also enhances surrounding aesthetics, minimises noise,
improves air quality, manages stormwater and provides both ecological and
social benefits when implemented.
Challenges of the proposed solution
include installation, cost, and maintenance. Both primary and secondary
research such as interviews and guidelines found on the NParks website were
used to support the team’s proposal and have been included.
This project has been developed in
response to the request for proposal on developing solution of an environmental
problem.
According to Iso (2019), as the weather gets warmer due to global warming, Singaporeans
tend to rely on cooling appliances for their own purposes. This contributes to
higher air-conditioning demands, which give rise to the increase in greenhouse
gaseous emissions. As a result, a vicious cycle is formed which would further
aggravate the UHI effect should there be no actions taken.
The rise in urbanisation
along with variations in the man-made global warming effects lead to the
increase of the surface temperature. According to Meteorological Service
Singapore (MSS) (n.d.), “Eight of the ten
warmest years on record in Singapore have occurred in the 21st century and all
the ten warmest years are since 1997.” The surface air temperature has increased at an average of 0.25°C per decade
between 1948 and 2017. The graph of the annual surface temperature is shown in
Appendix A.
As demonstrated on the
graph in Appendix A, the rising temperature is an issue of concern and is in
dire need of a solution to address the UHI effect in Singapore. The UHI effect will
continue to exacerbate the frequency of heat waves. Residents from the
vulnerable age groups such as children, elderly, and those with existing
medical conditions, are at particular risk.
Apart from affecting
the residents, the rising of surface temperatures also concerns the government and
they are currently bringing their attention to alleviate the issue. According
to Parliament Singapore (2019), the Environment and Water Resources
Minister, Masagos Zulkifli, addressed the need for mitigating the UHI effect in
Singapore. One of his suggested measures was to integrate
open spaces with greenery “to cool our island” through “shade and
evapotranspiration.”
With the aim to incorporate greenery in open spaces
and reduce surface temperature through evapotranspiration, the team suggest
that green roofing is a viable solution.
According to NParks (2017), green roofing is a method of planting
vegetation on the roof of a building. The plants of the green roof can absorb carbon dioxide, one of the most
abundant greenhouse gases, through the process of photosynthesis. As the plants
reduce carbon dioxide from the environment, they produce more oxygen and
improves the quality of air. In addition, as plants experience transpiration, they
release evaporated water which cools its surrounding environment. This brings
down the need for air-conditioning. This idea is supported by Norquist (2012) that
“a green roof would help reduce the air-conditioning demand.” Apart from
providing a cooling effect and releasing fresh air, green roofs help to reflect
solar radiation which further reduces the UHI effect.
An example of a successfully retrofitted green roof
on a building would be the Chicago City Hall. A green roof was added to the
11-storey Chicago City Hall building to test the benefits that it could provide
after Chicago experienced a heat wave in 1995, which took several lives of its
citizens. According to Dvorak and
Carroll (2008), the main cause of the heat wave was the UHI effect,
which was resulted from the heat in the city absorbed by concrete surfaces such
as its buildings and pavements. Due to the success of the City Hall’s green
roof, Chicago has planted more than 200 vegetated roofs in its city.
From the Chicago City Hall case study, the team sees
the need to incorporate the idea into the estate of HDB. The strategic location
of retrofitting the green roof would be the MSCP which is surrounded by high-rise HDB flats. The satellite
view of the MSCP is shown in Appendix C.
The team did a survey on ten multi-storey car
parks at Pioneer HDB estate during different periods of the day. From their
observation, out of the ten carparks, only one was seen with two cars at the
rooftop. The team
identified that there are a total of 2108 HDB carparks in Singapore, of which
2% of it consists of basement, covered, and mechanised carparks, 51% are
surface carparks and the remaining 47% are multi-storey carparks. These
statistics are presented in Appendix B.
Retrofitting the
rooftop of the multi-storey carpark with a green roof would be a viable
solution since nearly half of the HDB car parks consist of multi-storey car
park.
Installing green roofs
at every under-utilised open rooftop of HDB multi-storey car park would reduce
the temperature around the surrounding vicinity. However, there are still a lot of
under-utilised multi-storey car parks, especially at the rooftop. In order to
tackle the UHI effect, the team sees a need for the retrofitting of a green
roof at existing under-utilised MSCPs.
The purpose of this report is to propose to the estate management
department of Housing Development Board (HDB) to adopt green roof at existing
under-utilised MSCPs at the older estate. The implementation of this idea will
help to mitigate the UHI
effect.
The team’s proposed
solution to mitigate the UHI effect in Singapore is to retrofit green roof at
under-utilised top storey of HDB multi-storey car park. Frese (2016) stated
that a green roof relies mainly on sunlight and water to reduce the surrounding
temperature by evapotranspiration.
Some of the
considerations of retrofitting green roofs onto MSCPs rooftop depend on the
structural integrity and the budget allocation of each car park. In an
interview with Miss Nurul Sharfirin, a former Higher Estate Executive of HDB, she
stated that different estates or region would have different budget depending
on its size and maintenance. Most of the time the Town Council (TC) not HDB
maintains the MSCPs. In order to perform modification on an existing structure,
HDB, TC, and Governance, Risk management and Compliance (GRC) will have to
conduct a joint meeting to discuss on the issues or concerns that may arise
from the project.
To have a green roof
that suits the considerations (structural integrity of the MSCPs, cost, and maintenance),
there are two different types of green roofs that the team would like to
propose, namely the extensive and intensive green roof system.
Green Roof
Technology (n.d.) claimed that, an extensive green
roof is the lightest type of green roof. It weighs typically between 74 to 122
kg/m2. This dramatically reduces the amount of structural change that is
required for the car park. The weight of the soil is in proportion to its
growing medium depth which ranges from 3 to 5 inches deep.
Arabi, Shahidan, Kamal, Jaafar, and
Rakhshandehroo (2015) stated that, drought-resistant
plants such as sedums, mosses and, grasses are some of the plants used, due to
them having a shallow root system which requires minimal water. Getter and Rowe
(2006) mentioned that, the variety of plants are kept to a minimum to ensure
that every plant has similar moisture absorption content. They also require
limited fertilisers.
2.2.
Intensive Green Roof
According to Plant Connection Inc
(n.d.), an intensive green
roof can be installed at the better structural integrity of a building as it is
much heavier compared to the extensive green roof. The soil has a depth of 6
inches deep or more and weighs roughly around 100 kg/m2 when it is dry and 150 kg/m2
when fully soaked. Some of the crucial factors that need to be considered are
the irrigation and drainage system as they may overload the roof’s structure.
According to Getter and Rowe (2006), with a deeper soil medium, this system allows the
plantation of the different types of trees or plants of shape and sizes.
Typically, the roof will include benches, walkways and shelters for the public
to rest or even interact with the natural features.
However, this design requires more maintenance
due to the wide variety of plants. This will lead to an increase in pests and
weeds. In addition to that, fertilisers, and the amount of water or irrigation
needed plays a huge part in maintaining this design. It typically stays more
appealing during the dry weather.
The main benefit of a green roof is to reduce the surface
temperature in the estate. In addition, according to Semaan and Pearce (2016), it
provides other benefits such as improving surrounding air quality, reducing
surrounding noise, managing stormwater, providing both ecological and social
benefits.
- Reducing surface
temperature
The green roof reduces the surface temperature at the estate,
provides thermal comfort to the residents and absorbs fewer solar radiations
acting as a buffer in between the sun’s radiation and the concrete surface of
multi-storey carpark rooftop.
- Improving surrounding air quality
The green roof captures harmful fine dust particles from the air
and improves the quality of the air.
- Reducing surrounding noise
The green roof absorbs the sound waves and reduces the noise
level significantly as compared to traditional rooftop caused by the vehicles
in the carpark.
- Improving stormwater management
The green roof holds the water for a period to
reduce or delay the flow of water to the drainage system. It also helps
evaporate the rainwater, by releasing it back into the atmosphere instead of
drains and sewers.
- Providing ecological benefits
The green roof enhances the aesthetic of the estate and reduces
the sunlight glare as it does not reflect it.
- Providing social benefits
The green roof
provides relief from the concrete surface of the rooftop. The presence of green
has a relaxing psychological effect on the residents. It also substantially
enhances residential property value to the estate.
In this section, the
challenges, as well as the feasibility of the proposed solutions, will be
discussed.
Even though this
proposed solution could help to mitigate the UHI effect, there are a few
concerns that need to be considered. These primary concerns include structural
limitations, cost, and maintenance.
As seen from the Figure 3 in Appendix C, an average car-park can contain about 74
numbers of cars per storey and as mentioned by Miller-Wilson (n.d.), the
average weight of a car is approximately two tons.
Salter (2010) argued
that, an extensive green
roof does not pose any weight problem since it is light. However, the intensive
green roof could alter the structural weight of the car-park due to some of its
properties. The planting medium of this design ranges in between 6 to 18 inches
deep and subsequently, the weight of the plant increases after some of the time.
In addition, during the wet season, this design could potentially be fully
soaked which further stresses the loading capacity of the car-park. Since the
car-park rooftop has a flat surface, planting the green roof would not cause a
problem.
As argued by Castleton, Stovin, Beck, and Davison (2010), although
the green roof helps to reduce the energy cost in the surrounding, it is rather
costly in installing and maintaining the green roof. The table below shows some
of the factors that need to be considered.
Table 1: Cost factors between installation and maintenance.
Installation
of Green Roof
|
Maintenance
of Green Roof
|
1.
Purchasing of different types of soil and plants.
2.
Buying of planting materials and necessary equipment.
3.
Installing cost for the irrigation and drainage system.
4.
Purchasing of fertilisers
5.
Transportation cost.
6.
Hiring green roof professionals.
|
1.
Purchasing of pesticides and herbicides.
2.
Repairing cost of leakages from water or sprinkler.
3.
Replacing dead plants.
4.
Regular inspection and cleaning cost for the green roof.
5.
Transportation cost.
6.
Hiring green roof professionals.
|
NParks
(2012) asserted that, maintaining the green roof is a time-consuming and
tedious job as it ensures sufficient irrigation and fertilisers for the plants
to grow well. In addition, daily inspection is required to check for any types
of damages to the plants or leakages from the water tank or sprinklers. Pests
and weeds will also affect the growth of the plant. If the green roof is not
maintained regularly, it will result in an increase in plant losses, and the
cost of replacing it would be significantly high. Furthermore, the green roof
may turn into an untidy and unhygienic place.
5. Methodology
and Procedure
5.1.
Primary Research
The team conducted an
interview with Dr Kum Yung Juan, who is an assistant professor in the Singapore
Institute of Technology (SIT) to understand better about the challenges and
limitations of retrofitting a green roof. In terms of engineering, it was
concluded that there were no restrictions in retrofitting a green roof in the
rooftop of the MSCPs as the rooftop can withstand a heavy load approximately
148 tons (mentioned in 4.1.).
From the discussion,
the team was clear that the aspect of retrofitting the green roof on existing
MSCPs was possible. However, the team was not sure of the bureaucracy and
management structure of HDB, the stakeholder. In order to understand how
HDB operates when dealing with the estate management of buildings and
amenities, the team conducted an interview with Miss Nurul Sharfirin, a former
higher estate executive in HDB. The team was provided with information on how
HDB plans for an estate as well as maintaining existing MSCPs.
5.2.
Secondary Research
The main source of our secondary
research is from NParks (n.d.). This website provides information on skyrise
gardening, planning, design and safety considerations, types of plants to
consider, frequently asked questions and case studies of other projects that
adopted the green roof concept. Additional sources include online publication,
handbooks and websites which supported the contents in this report are Bringing
Greenery Skywards (2017), Guidelines on Planting of Trees, Palms and Tall
Shrubs on Rooftop (2012), Frese (2016). As for
figures, they are sourced from Meteorological Service Singapore (n.d.).
Wong and Yu (2005)
observe that the UHI effect is a reciprocal effect of rising surface air
temperature. The lack of natural landscape on buildings lead to an increase of
the surface air temperature as the heat gets trapped in between buildings.
Since urbanisation is projected to accelerate in the coming years, mitigation
measures must be implemented to curb the UHI effect. With the presence of the green
roof on MSCP, it can significantly reduce the UHI effect in the estate. Not
only does the proposed idea of retrofitting a green roof on MSCP reduces noise,
improves air quality, manages stormwater, provides both ecological and social
benefits, it also reduces the surface temperature through evapotranspiration
which eventually reduces the UHI effect in the estate. In addition, a green
roof creates beneficial means to both the community and the environment.
