Technical Report Final

Executive Summary

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.

1.     Introduction

1.1.        Background Information

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.

1.2.        Problem Statement

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.

1.3.        Purpose Statement

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.

2.     Proposed Solution

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.

2.1.        Extensive Green Roof

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.

3.     Benefits of Proposed Solutions

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.

1. 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.

2. Improving surrounding air quality

The green roof captures harmful fine dust particles from the air and improves the quality of the air.

3. 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.

4. 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.

5. Providing ecological benefits

The green roof enhances the aesthetic of the estate and reduces the sunlight glare as it does not reflect it.

6. 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.

4.     Proposal Evaluation

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.

4.1.        Structural Limitations

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.

4.2.        Cost

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.

 

4.3.        Maintenance

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.).

6.       Conclusion

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.