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.
5.1. 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.
