Safe Design and Management of Vertical Greenery Systems Michael Behm 52 and Poh Choon Hock 53 52 East Carolina University, USA 53 Centre for Urban Greenery and Ecology, Singapore Abstract In Singapore, vertical greenery systems are becoming increasingly popular as a green feature within the urban built environment. These systems can present challenges for workers including safe access and fall protection. There is no guidance internationally and no archival research that evaluates worker safety associated with vertical greenery. Thirteen vertical greenery systems were visited with observations focusing largely on safe access, fall protection, and plant selection. The paper will focus on the observations and the state of safety practices for vertical greenery systems in Singapore. Recommendations are offered for safe design and management, and for plant selection. Innovative designs that promote good practice will be reviewed. This research is part of a larger study focused on the safe design of skyrise greenery with the Singapore National Parks Board and the Centre for Urban Greenery and Ecology. Keywords Green walls, built environment, architecture, engineering, Singapore. INTRODUCTION There is a growing interest in the utilization of greenery systems on the built environment. Proponents of urban ecology promote green facades and living walls as one means to help improve and restore the urban environment (Francis and Lorimer, 2011; Köhler, 2008). The widespread use of vertical greenery systems on the numerous building walls in cities represents a great potential in reducing urban noises generated from traffic and machines, mitigating the urban heat island effect, and transforming the urban landscape (Wong et al., 2010a). Because of the increased use of greenery systems, their design and maintenance have to be investigated more thoroughly in order to determine their sustainability (Emilsson et al., 2007), and to develop standards and guidelines (Dvorak and Volder, 2010). Designing vertical greenery systems can be difficult in urban areas due to the spatial complexity of both the physical and social landscapes, both of which are important in determining whether green walls are likely to be installed, and whether they are likely to be successful (Francis and Lorimer, 2011). Singapore is one of the world leaders in urban greenery including vertical greenery system and is transforming itself from a Garden City to a City-in-a-Garden. The National Parks Board (NParks) has introduced the Skyrise Greenery Incentive Scheme (SGIS); NParks will fund up to 50 percent of installation costs of green roofs and vertical greenery (NParks, 2012). In Singapore, Wong et al. (2010b) found that locally, there is a lack of technical information, maintenance instructions, and information on plants suitable for vertical greenery systems. The NParks Centre for Urban Greenery and 52 behmm@ecu.edu 53 poh_choon_hock@nparks.gov.sg 195
Ecology (CUGE) produces technical guidelines on urban greenery systems, including a guideline on Safe Design for Rooftop Greenery. Vertical greenery systems are not included in that guideline. Wong et al. (2010b) surveyed Singapore architects, landscape architects, developers, governmental agencies, and residents and inquired about perceptions of vertical greenery. All five groups agreed that vertical greenery systems: Can add visual interest to plain walls and roofs while beautifying the urban environment. Allow for the reintroduction of biodiversity into the urban environment as well as help to preserve and protect the habitats of plants and animals. Have therapeutic effects by improving the health of its users. Provide better acoustic insulation resulting in noise reduction in the building s vicinity and interior. Increase a building s property value and marketability. Increase visual interest and beautify the urban environment. Help to improve air quality by acting as a filter trapping airborne dust particles. Result in closer and more frequent contact between city dwellers and greenery, therefore enhancing the psychological well being of city dwellers. Vertical greenery systems must be maintained. Plants need an appropriate amount of sunlight, nutrients and water. Plants on green walls, when given suitable growth conditions (i.e. adequate sunlight, plant nutrients and moisture with sufficient rooting space and growth medium, etc.) will flourish. Given the right environment, some plant species can grow very lush within months and where necessary may need to be appropriately pruned back to meet the expectations of building owners and users. Not unlike general landscaping, plants on green walls will require periodic general maintenance such as weeding, irrigation, fertigation, etc. On the other hand, when the environment conditions are less conducive for plant growth, plant health may decline due to a range of reasons. Dead plants may be required to be removed and replaced with new plants, etc. All of the above-mentioned greenery maintenance activities require workers to access these vertical vegetated surfaces. Plant-selection, plant-health and performance do affect frequency and types of maintenance and inspection activities. The maintenance requirements of vertical greenery systems increase the frequency of risk to workers compared to working at height in normal building work. This paper focuses on upstream design and management planning to recognize those risks and solving them in the design phases of the project. The purpose of this paper is to provide observations and the state of safe design practices of vertical greenery systems in Singapore. Safe design of the built environment is a central theme of this and previous International Council for Research and Innovation in Building and Construction conferences. Isolating individual building elements has previously generated safe design ideas to reduce eventual risk to workers within the built environment. METHOD Thirteen vertical greenery systems in Singapore were visited and evaluated them for safe access, fall protection, and other potential hazards (i.e., mosquito breeding). The sample was a convenience sample; contacts through CUGE were utilized to gain access. Photographs were taken and discussed by the two researchers. The presentation of these findings is part of a larger study on the safe design of skyrise greenery. A manuscript has been submitted to the journal, Smart and Sustainable Built Environment highlighting the quantitative data and broader results. 196
RESULTS AND DISCUSSION The design of vertical greenery systems needs to consider safe access and fall protection for both installation and maintenance activities. Because there are many equipment types that can be utilized to access high vertical areas, the access design and area around the vertical greenery system must be accounted for and be congruent with the height of the green wall. Designers should involve installation and landscape maintenance company representatives during the design phase to understand the equipment available, its dimensions, and cost. Throughout the site visits, 100 percent access to all vertical green areas was a concern. Even when it appeared that an aerial lift could access the greenery, there were sometimes concerns about accessing the top corner, for example, due to a desk, lighting fixture, or other building components blocking access to a specific location. Generally speaking, accidents are rare events, and it is these specific situations which increase risk on an otherwise safely designed system. Due to the height, varying angles, and corners that appeared out of reach or difficult to access, the researchers felt that workers might take short-cuts in order to maintain all areas. This should be a focus of safe design. Cameron et al. (2007) noted that during maintenance tasks of short duration and often precarious nature of access to the task, the risk of falls is high. Due to the temporary nature of some maintenance tasks, workers can be tempted to take on unacceptably high risks especially if the task duration is short. Some access can be from the roof with gondolas as would be utilized for window cleaning. This can be quite expensive. In discussions with one safety manager representing the owner of a green wall in the design phase, the gondola system seemed to be the only method for access. Thinking about how the vertical greenery will be safely maintained in the design phase will allow the designer, owner, and other team members to consider all options. In the design phase, the dimensions of equipment necessary for access of all areas should be specified. One facility manager recommended that a designated storage space be designed into the building specifically for the purpose of storing necessary equipment. The manager s rationale was that then there would be no assumptions as to the type of maintenance equipment needed and safety would be considered and perhaps other options developed. These storage and equipment specifications should be communicated to the building owner so that their facility staff can understand the requirements. Installation and maintenance companies can build safety into their bids for the kinds of equipment that will be needed for safe access. Workers access can be designed in to and behind the vertical greenery system. Numerous examples of this type of access were observed; this is a preferred method for safe access. One example is an indoor green wall with the plants growing up a roped trellis from planter boxes. Access is through a locked entrance on to a built-in platform. Maintenance is performed from the platform as shown in Figure 1. Figure 2 shows the vegetation from a frontal view with the platform in the rear. 197
Figure 1. Platform for maintenance Figure 2. Front view Figure 3 shows the entrance way with a door to an access platform behind another interior green wall with planter boxes. A vertical cat ladder allows worker to access each floor. Figure 4 shows a close-up view of the planter boxes with ladder on left. Figure 3. Access area behind greenery Figure 4. Planter boxes; cat ladder Figure 5 shows an exterior vertical greenery system with catwalk behind plants that grow up a steel mesh. A walkway is provided for good worker access. The letter A depicts the area that the worker would stand to maintain the plants; the planter box provides a barrier and acts as fall protection at that point. However, the system is not continuous; gaps exist with no guardrail and are shown by the letter B in Figure 5. The worker needs to use this area to get to each planter box, and no work is performed here, thus the frequency risk of falling is low. However, there are no toeboards here that would prevent tools from sliding off the work area falling to the ground below. The frequency risk again is low but the severity risk is high, and could have been eliminated in the design phase with a barrier such as a standard toeboard. 198
Figure 5. Platform access Another interior vertical greenery example is highlighted in Figures 6 and 7. A small cavity for a worker is designed behind the greenery. The worker accesses the greenery from platform with guardrails as shown in Figure 6. Figure 7 shows the space where the maintenance work is performed and that the worker can access the plants for routine maintenance and re-planting. Figure 6. Access is behind greenery Figure 7. Photo from behind greenery 199
Some vertical greenery walls can only be accessed and maintained from the front (these vertical greenery systems are installed against a blank wall surface). For walls that can only be accessed and maintained from the front, those designed on or close to ground level are less difficult to access and thus do not discourage more frequent maintenance. As the height of the vertical greenery wall increases, aerial lifts of varying sizes will need to be utilized to reach the tall areas; therefore the design should consider the type of lift necessary when designing to allow for such space. Safe design can allow for sufficient room so that all areas of the greenery can be safely accessed by an aerial lift, etc. When designing for the maintenance activities, ensure the access space for aerial lifts or other devices is flat and free of unique hazards (slopes, water, etc.) that might hinder movement of the bucket truck, aerial lift, etc. Traditionally, solving fall protection and access issues focuses on getting employees to the greenery (ladders, aerial lifts, etc.) and protecting them once there (anchor points, harnesses, etc.). However, designers should consider options such as moving the greenery to the worker rather than thinking about moving workers to the greenery. For example, on a tall vertical greenery system where aerial platforms would be inconvenient, the greenery systems was placed on hinged type doors which open behind the system to a secured access platform to allow for safe worker access. Another innovative design was on an exterior vertical column on a sixth floor balcony. Rather than bringing the worker outside the guardrail system to access the vegetation using cumbersome fall protection systems, the column rotated and thus the worker could access each of the six sides safely from the terrace. PLANT SELECTION Plant selection should respect the site s microclimatic conditions. Every location is unique with its distinct environment and microclimatic conditions, which must be considered when selecting plants for green walls. For example, a green wall surface may be shaded by surrounding buildings and urban forms and do not receive generous amount of sunlight. In such an environment, sun-loving plants will not grow well and shade-loving plants may be more suitable. Some green walls installed at higher altitude may be exposed to more wind loads. Exposed to wind draughts, moisture is lost at a faster rate and the selected plants will need to be more drought-tolerant. It is to be noted that plant species appropriately selected for the given site conditions will have a higher chance of survival. Plant selection should respect the envisaged green wall design. Plants come in a variety of shapes, colors, sizes and grown-forms. For example, climber-plant will need supports that assist its general upward growth towards the sunlight overhead due to phototropism. Trailing-plant cascades beautifully downwards and is best planted on a raised planter or location to allow the foliage to drape. Upright shrubs, when planted on a green wall, tend to grow and extend outward before arching gently towards the sunlight overhead. Some fine-leaf ground covers on a green wall acquire a lush undulating billowing form with adequate growth over time. With plant growth, the plant forms change with time. There will be times when the achieved plant forms are less desirable and may need to be managed via judicious clipping in order to be more aligned with envisaged green wall design. Different plant species will have different maintenance needs at different growth-stages and these will influence the frequencies and types of maintenance and inspection activities on the green wall. MOSQUITO CONTROL Mosquitoes transmit diseases such as dengue fever/dengue haemorrhagic fever, malaria and Japanese encephalitis (National Environment Agency, 1995). Mosquitoes breed in stagnant water. In Singapore s tropical climate, taking precautions are especially 200
important. During the site visits, the potential for optimum mosquito breeding conditions were observed. There was one vertical greenery structure that appeared to be conducive for mosquito breeding due to the shape of the steel structure that supported the plantings. Figure 8 shows the V-shaped angled steel where there was evidence of water pooling (see letter A and arrow in the photo). Future designs should consider alternatives to eradicate water pooling. Figure 8. Potential for water pooling MANAGEMENT AND PLANNING The two main issues identified are site access and fall protection. Management and planning before work will complement safe design strategies. All work should be adequately assessed for potential safety risks before workers come to the built environment site. Proper personal protective equipment (PPE) (harness and lifeline) to utilize any designed-in-place fall protection anchoring points should be arranged for in the work planning. PPE requirements should be conventional (similar to gondolas, roof edge PPE needs.) Work procedures, expectations, tools, materials, handling of materials, material replacement, material volumes, may be different from conventional façade window cleaning. Potential falling plant debris (of various sizes, quantity) may need to be better managed. Perhaps larger garbage bags in the gondolas as they prune and clear out plant debris. These job specific requirements, related to gardening in a skyrise context, may need to be addressed through training of workers as well as written clearly in the management plans. CONCLUSIONS This paper described observations and the state of safety practices for vertical greenery systems in Singapore. Singapore is one of the world leaders in urban greenery including vertical greenery system and is transforming itself from a Garden City to a City-in-a- Garden. CUGE develops research and technical guidance for skyrise greenery. Future revisions of the CUGE Guidelines on Design for Safety on Rooftop Greenery should be expanded to include the observations and recommendations of vertical greenery from this study. Building owners should explicitly request that designers consider safety during the design of vertical greenery systems. Designers should utilize the guidance provided here and also include a safety professional with construction or landscape experience during the conceptual and detailed design. The ideology of safe design of the built environment is congruent with the Singapore Workplace Safety and Health Council s safe design initiatives (Workplace Safety and Health Council, 2008). As urban and skyrise greenery 201
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