Study on Landscape Construction of Sustainable Urban Rooftop Farms

College of City Construction, Jiangxi Normal University, Nanchang 330022, China

Abstract From the perspective ecological benefit, economic benefit and social benefit, this paper analyzes the necessities of building urban rooftop farm under the demand of sustainable life of urban residents, and puts forward the design strategy of rooftop farm landscape construction, in order to provide a scientific basis for the construction of sustainable roof farm landscape, and to achieve the planning and design of the future lifestyle of urban residents.

Key words Rooftop farms, Landscape construction, Sustainability

1 Introduction

In 2008, the global urban population exceeded the rural population for the first time, which means that from this node, the city has become the main form of human settlement[1]. It is estimated that the world’s urban population will reach 5.5 billion by 2025, 80% of whom will live in urban centers in developing countries[2]. China’s urbanization rate exceeded 50% in 2011 and reached 54.77% in 2014, becoming one of the fastest urbanizing countries in the world[1]. With the aggravation of urban problems, such as land scarcity, energy scarcity, food crisis, and food security, the sustainable development of cities has been unprecedentedly tested. People have realized that it is of great significance to re-develop agriculture in cities[2-3]. In 1998, Professor Dickson Despommier of Columbia University in the United States first came up with the idea of "vertical farms" to produce food for people’s lives in reinforced concrete urban forests. This triggered a great interest and a design boom in the construction industry[3]. Many scholars believe that the development of rooftop agriculture can not only make full use of urban idle space, provide more green space for the city, but also absorb dust in the air, thus reducing the degree of haze pollution. Different from the traditional roof greening, the rooftop farm can make use of the ornamental nature of the crops for the landscape appreciation; at the same time, the utility of the crops can be brought into play, and the actual material output can be obtained[4]. Twelfth Five-Year Plan in China proposes building a green, resource-saving, environment-friendly society, which provides a good opportunity for the development of urban rooftop crops landscape[5].

2 Necessities of building rooftop farms

Rooftop farm, using the roof space to develop agriculture, is a new type of modern agriculture that transfers the cultivation environment of all kinds of crops to the roof of the building and has a certain scale. It is a new type of urban roof greening formed by combining urban green infrastructure, ecological technology, and advanced design concepts. It is a complex closely related to urban planning, green building, landscape ecology, circular economy and community neighborhood[2-3,6]. The roof of most cities in our country has been the passive space in the city for a long time. It is calculated that most of China’s existing roof area of 730 000 ha, is completely idle[7]. Therefore, it is necessary to give full play to the great potential of roof for agricultural production, to use roof space to inject new vitality into the city, and to bring ecological, economic and social benefits.

2.1EcologicalbenefitsofrooftopfarmsRooftop farms can improve heat island effect, save energy and reduce consumption, improve air quality, reduce noise pollution, improve rainwater and runoff, increase biodiversity and so on. And through the vegetation, the soil and so on, it forms an effective ecological environment, and forms a microclimate environment in part of the city, thus bringing the good ecological benefit[6]. First, the emergence of rooftop agriculture has changed the physical properties of rooftop floors, reducing direct sunlight on the floor. At the same time, because the crop transpiration and photosynthesis can absorb the radiant heat energy effectively, the storage heat of the roof is greatly reduced, which alleviates the urban heat island effect[2]. A UNEP study found that if a city’s roof greening rate is greater than 70%, CO2levels above the city would drop by 80%, and the heat island effect would disappear altogether[3]. Second, the rooftop farm crop can also use its evapotranspiration to adjust and store rain water, to ease the drainage pressure of urban drainage pipes, which is an effective sponge body to control urban waterlogging in the construction of sponge cities in our country. Third, crops can also absorb dust over the city and absorb CO2, and release oxygen, play a role in purifying the air. Compared with the ground crops, rooftop crops grow in a higher position, dust reduction effect is better[5]. Fourth, the green planting layer on the roof can isolate the high temperature produced by the direct sunlight, and reduce the indoor temperature during the high temperature period in summer by 5℃ and 6℃. The room temperature can be increased by 2℃ to 3℃ in the cold winter period, which can save at least 50% of the energy used for air conditioning and 50% of the heating energy in winter[4]for the top floor of the building. Fifth, rooftop farm can play a better role in reducing noise. The main sources of urban noise are traffic noise, industrial noise, social noise and construction noise, which also threaten the physical and mental health of urban residents. Rooftop farms can absorb and block noise through foliage. It is estimated that 40 m wide forest belt can reduce noise by 10 to 15 dB, so planting green plants on the roof is an economic and environmentally friendly noise reduction method[2]. Stevenetal. found that the cultivation matrix also has a certain effect of noise reduction, when the thickness is 12 cm, it can reduce the noise by about 40 dB; when the thickness is 20 cm, the noise level can be reduced by 46 to 50 dB[2]. Finally, rooftop farms can create a good micro-ecological environment. It can not only enrich the urban species diversity by attracting birds, insects and so on, but also better control the soil quality, water quality and pest prevention and other aspects because of its relatively independent small ecological circle.

2.2EconomicbenefitsofrooftopfarmsRooftop farms can save money on roof maintenance. For bare roofs that are not planted with greenery, if the service life exceeds 10 years, water leakage will occur, and the maintenance cost of repeated leakage repair will remain high[2]. The roofs planted with greenery will form a protective layer, which can effectively avoid the adverse effects of temperature difference between day and night, acid rain and ultraviolet radiation on the roof of the building. It can experience years or even decades of no leakage, extending the service life of the building[1-2]. Second, rooftop farms can save money on construction. The cultivation matrix of the roof crops can be used as the additional insulation layer on the floor, which can improve the thermal environment of the indoor space of the building, reduce the use of air conditioning in summer and winter, and thus save expenses. Third, the production of rooftop farms can bring economic benefits. Compared with the ordinary green roof, which has the natural disadvantage of only input and no output in economy, the rooftop farms can recover the construction cost and even produce economic benefits under the condition of reasonable operation. Fourth, rooftop farms can save the cost of transporting vegetables. Rooftop farming, this form of crop cultivation, can avoid the loss of vegetables in long-distance transport, thereby providing the public with fresh vegetables, and reducing the cost of transportation of vegetables. Finally, rooftop farms may lead to real estate appreciation. Studies by British scholars show that rooftop gardens in the UK can increase the value of a house by 10% to 30%[7].

2.3SocialbenefitsofrooftopfarmsRooftop farms are, to some extent, an effective means of alleviating current social problems. Compared with the traditional agricultural landscape, the rooftop farm can not only save the urban land and play the role of landscape ecology, but also give full play to the sense of responsibility and enthusiasm of the citizens to the society, and promote the communication between the neighbors in the urban community in a positive way, so as to ease the pressure of city life. At the same time, the roofs of urban buildings are mostly bare concrete, and some of the roofs of buildings also have the phenomenon of reflecting dazzling light, causing serious light pollution[8]. Rooftop farms can make rational use of urban roof space, enrich the level of urban landscape, and at the same time weaken the boring feeling brought by the building, and make the city more natural and humane.

3 Landscape construction strategy of rooftop farm

3.1SafetyconsiderationsSafety is the primary consideration in the design of rooftop farms. First of all, we should consider increasing the load bearing capacity of the roof loaded with plants, and ensure that the building can bear the load to meet the demand. Roof crop landscape is usually constructed in two ways: soil cultivation and box cultivation[5]. The selection of planting bed, soil cultivation or box cultivation, water planting or spray culture, and the determination of the depth of soil cover should be based on building loads. Secondly, the safety of roof waterproofing should be ensured. The construction of rooftop farm requires higher load and waterproofing of the building, so it is necessary to avoid destroying the original waterproof layer when building rooftop farm, and to set up isolation layer, filter layer and drainage layer according to the actual situation of the farm. For example, in Shanghai’s "Sky Vegetable Garden (V-Roof)" project, the rooftop of farms is accessible rooftop with a load bearing capacity of more than 300 kg. Portable planting boxes are used as basic planting equipment on rooftop farms. The planting boxes are filled with organic light soil, weighing 50-100 kg/m2, in accordance with roof load-bearing requirements[7]. The rooftop farm landscape pieces also need to be able to withstand the temperature changes of sudden cold and heat of the roof. Plastic steel or aluminum frames and materials suitable for all kinds of weather can be used on roofs. At the same time, as a result of the strong roof wind, light furniture needs to be fixed, in order to eliminate hidden dangers[6].

3.2SelectionofvegetationThe vegetation selection of rooftop farms should take full account of the different climatic characteristics, the surrounding environment and the special habitat conditions of roofs. According to the variety and growth characteristics of crops, the different farm landscape in four seasons can be created to achieve the double value of production and aesthetics. Rooftop farm plants that can be selected, cover garden plants and crops. Garden plants can create a landscape, increase the richness of space, such asOxaliscorymbosa,Zephyranthescandida, andCampsisgrandiflora[6]. Crops can be reasonably selected according to time and demand. According to the growth characteristics of crops, the crops in spring are relatively short, the landscape level is relatively single, the farm is mainly green, but there are also varying degrees of changes. In summer, crops grow rapidly, and the height of tomato, zucchini and other crops will obscure the view, at this time, the farm landscape layer is much richer, and color is also varied. In autumn, the fruits of the crops can bring vitality to the rooftop farms. In winter, other plants are needed to replace crops to maintain the fertility of the soil and sustain the rooftop landscape. In the process of vegetation allocation, the changes of color, shape, volume and location of crops should be fully considered, so as to create rooftop farms with productive and aesthetic value[5]. It not only reflects the cultural characteristics of agricultural landscape space, but also combines the agricultural landscape and garden landscape as a whole, giving different landscape construction ideas to the overall design, guiding the use groups to start thinking, play imagination, and integrate into nature.

3.3FunctionalzoningThe functional zoning of rooftop farms should fully consider the needs of different groups of people in the field of space; in the construction of landscape, we can set up some space with different shape, size and open degree, which can be chosen by different groups.For example, the exhibition area can display the richness of species through vegetables, flowers, and medicinal plants, creating different perceptual experience spaces, enriching visitors’ multidimensional feelings, and giving consideration to both function and beauty. Vegetable planting area is set up to achieve the real production function, which can produce fresh vegetables, and also can increase the value of land use, reduce the necessary economic expenditure. Rental areas can meet the needs of some people who are eager to experience planting on their own. In the city, there are few places where people can engage in planting activities, the actual planting activities can not only increase the hands-on ability, but also play a certain educational role[6]. For example, the Guangsangyuan Agricultural Popular Science and Culture Park, Futian District, Shenzhen City, has provided 500 planting beds for planting pollution-free vegetables, as well as materials and tools such as vegetable seeds, organic fertilizers, hoes, and sharp shovels for the citizens[5].

The functional zoning of the rooftop farm should also take into account the design form, so that the overall design of the roof is full of landscape feature. Through the creation of different visual, olfactory, auditory space, it can meet the needs of different groups for exploration and space. The design forms are mainly linear space and curved space. The linear space can create a quiet and open atmosphere. The curved space gives people a smooth, natural feeling. For example, the design of Gary Comer Youth Center Roof Garden in the United States uses geometric shapes to divide the entire roof, and the combination of lines and circles enhances the rhythm of the entire roof[5]. Tianyou Landscape Rooftop Farm in Tianjin uses the landscape elements of crops to break the traditional plant landscape construction methods. The roof space is reasonably divided into four areas: nursery area, exhibition area, activity area and mass production area. so it gives full play to the functionality of each space[4]. With the combination of landscape and agriculture, the interaction between user and landscape is enhanced.

3.4EconomicandtechnologicalmeansThe landscape construction and operation of rooftop crops need to be supported by corresponding economic and technical means for maintenance. In terms of economic means, we take Brooklyn Farm in New York, USA for example. The farm is a for-profit rooftop farm that produces about 2 268 kg organic food each year[5]. The farm uses organic farming to grow crops and raise poultry and bees. The harvested produce is not only sold at the local agricultural trade fair, but also made available to CSA members and several restaurants, with a total of 54 431 kg vegetables sold so far[5,8]. In addition to making farm produce, Brooklyn Farm also provides consulting and installation services on rooftop farms to organizations and individuals from all over the world[5]. This kind of management mode is the guarantee that maintains the rooftop farm to be able to run for a long time. In terms of technological means, the rooftop farm’s automation irrigation, supporting, pest control, energy saving and other aspects need advanced technology for maintenance and innovation. Rain water circulation system on roof can carry out rain water collection and the automation seepage irrigation, so as to enhance rain water use efficiency, and alleviate the urban waterlogging. The kitchen waste, human excreta, sludge and waste water produced in the city can be used as valuable organic fertilizer rich in a variety of nutrients after bio-safety disposal[1]. The relatively independent environment of the roof makes pest control more controllable, and we can use natural insecticides or insecticidal equipment with physical properties. With the combination of rooftop farm and photovoltaic module, we can make full use of solar energy to solve the power supply of rooftop farm and realize the self-sufficiency of electricity. These application technologies are important technical support for the construction and implementation of sustainable urban rooftop farms.

4 Conclusions

The construction of ecological and land-saving city has become an inevitable choice for mankind to cope with the challenge of ecological environment deterioration, to get rid of the plight of cultivated land and food shortage, and to explore the sustainable development of human society. The construction of rooftop farms meets the needs of sustainable urban development. Rooftop farms play an active role in society, economy, ecology, culture and so on. In the design, we should regard it as a kind of social landscape and endow it with more comprehensive functions, while considering its economic and ecological benefits. Looking from the present situation of development, the roof farming in our country started relatively late, on the basis of the joint participation and active cooperation of the government, enterprises, organizations, residents and other actors, we should optimize and support the relevant policies and regulations, management systems, technical means and so on in an all-round way, in order to build a suitable environment for the survival and development of rooftop farms, and provide a guarantee for the sustainable development of urban rooftop farms.