Why is the development of green roofs slow in my country?

Since the 1960s, my country has begun to carry out research on roof gardens and roof greening technologies. In the 1970s, my country's first roof garden was built on the 10th floor roof of Guangzhou Dongfang Hotel. It was a roof garden built in synchronization with the building according to a unified planning and design. In 1983, Beijing built the five-star Great Wall Hotel, and built the first large-scale open-air roof garden in northern my country on the low-rise roof on the west side of the main hotel building.

   With the intensification of urbanization in my country, the green space in urban built-up areas is obviously insufficient. The implementation of roof greening, improving urban green coverage, and improving urban ecology and landscape benefits have received more and more attention. As a result, first-tier, second-tier and third-tier cities have successively carried out roof greening construction in various forms.

  Although the relevant concepts are mature and the materials are dazzling and constantly being upgraded, the expansion of the field of green roofs is still relatively slow, and the quality of the completed projects is also uneven. Among them, there are some problems from preliminary planning, design, construction, and even later maintenance. At present, the country is vigorously controlling smog pollution and advocating the construction of sponge cities. Under this favorable situation, how can roof greening take advantage of the situation to achieve greater development, so that "troubling things" will no longer be troublesome?

To ensure engineering quality, technical materials need to be checked

With the continuous improvement of social attention, more and more investors from inside and outside the industry have joined the ranks of the research and development of roof greening technology. Although it started late, after several years of hard work, my country's existing roof greening technology and materials have already competed with developed countries in Europe and the United States. The level is not much different. Compared with the high-level "hardware", the "software" level of professional ability of roof greening skilled workers is shameful. Either based on cost control, or due to lack of awareness, many companies are consciously or unintentionally "omitting" the important basic work of professional technical training.

"Compared with ground greening, our group does not have many roof greening projects every year. As a very professional project, it is very important to pay attention to the construction professionalism of roof greening, but now the company wants to recruit professional construction and maintenance personnel, which is quite difficult. Great." Wang Da, chairman of Jianwang Group, is quite distressed about the current situation of tight roof greening manpower, "The construction personnel are not very professional, which will inevitably affect the control of engineering details and bury hidden dangers to the quality of the project, and there is no scientific management. It is impossible to talk about the preservation and even sustainable development of existing achievements.”

"The quality of roof greening is not high, and it is closely related to the quality of construction and materials." Tan Yifan, director of the Institute of Landscape and Forestry Research, Shenzhen Garden Research Center, said that roof greening is essentially building greening. Therefore, its construction technology and product standards should be It is connected with the safety system and standard system of building construction. However, over the years, many places in China have always attributed roof greening to the category of landscaping, and participated in project bidding together with landscaping. Coupled with the low-cost bid winning model, the unit cost of roof greening has been severely reduced, so it is inevitable to use inferior materials. the result of.

   In addition, at present, there are no clear regulations on the certification of roof greening construction qualifications in China, and the practices vary from place to place. A large number of enterprises without roofing construction qualifications have entered this field, resulting in uneven construction quality. "Although many cities have issued local roof greening construction technical standards, the construction material standard system has not been established, so it is unavoidable that inferior materials are mixed into it." He said.

  Based on this, Tan Yifan believes that, as the competent department of the industry, the Ministry of Housing and Urban-Rural Development should take the lead in doing several things well. First, standardize the engineering attributes of roof greening, strictly distinguish between roof greening and ground greening, list roof greening separately in government investment projects, and formulate independent project cost standards. Secondly, standardize the construction qualifications of roof greening. Generally, landscaping enterprises must have corresponding qualifications before undertaking and constructing. Third, establish a standard system for roof greening products as soon as possible. Fourth, organize professional training and do a good job in industry-university-research linkage. "In short, the Ministry of Housing and Urban-Rural Development should increase the supervision of the industry, and can no longer allow the "barbaric" growth of the roof greening industry."

  Gao Xiang, general manager of Weihai Landscape Group Shanxi Branch, has always had a deep affection for roof greening. He believes that my country urgently needs to formulate roof greening plans. According to Gao Xiang, the implementation of a roof greening project in Germany must first formulate a detailed plan to guide the deployment of pre-construction and post-maintenance. "Roof greening projects planned for 30 to 40 years are very common in Germany. A clear planning goal will not only help to improve the construction level of roof greening technology, but also make the selection of materials more cautious. And this planning goal has an impact on An important factor in the sustainability of the return on investment in green roofs," he said.

"To successfully implement green roofs, we need to change our thinking and concepts." Gao Xiang emphasized that green roofs are not simply raised "ordinary" gardens, they are not natural landscapes, and there is nothing comparable in nature. . They are artificially designed and constructed systems, and as such are currently unknown to most designers, architects and constructors. "We have not yet been able to master and adapt to the special constraints of roof greening, including the necessary conditions for plants, which requires practitioners to conduct more in-depth research on roof greening construction technology and plants."

Plant selection should be based on planting experiments

During recess, many teachers and students of Shanghai Changning Experimental Primary School will come to the newly built roof garden. There are not only colorful flower beds, cool and beautiful water features, but also the fragrance of various plants that make people quite nostalgia. This garden is just a miniature version of the Shanghai rooftop garden. In the 1980s, the three-dimensional greening in Shencheng started. Today, the three-dimensional greening has accumulated to 2.2 million square meters, including 1.89 million square meters of roof greening, which is equivalent to the area of ​​20 people's parks. Not long ago, the "Amendment to Shanghai's Greening Regulations" was passed. This regulation, which has been implemented since October 1 this year, clearly stipulates that the city's new public buildings and the reconstruction and expansion of existing public buildings in the central city shall not exceed 50 meters in height. The flat roof is greened.

  Hu Yonghong, executive director of Shanghai Chenshan Botanical Garden, said that the scope suitable for building green roofs is limited, and only one permafrost layer problem can explain its limitations. "The type of roof greening should be determined according to the actual situation in each place. In particularly cold areas, roof greening is not recommended, otherwise the thicker planting soil layer to avoid the permafrost layer will impose more stringent requirements on the roof load. "

   As for the selection conditions of plant materials, the first point Hu Yonghong emphasized is that he should not only focus on landscape effects. "The primary function of green roofs is rainwater collection, which relies on the soil layer to store and intercept rainwater. Therefore, designers should calculate the thickness of the soil layer based on the local maximum daily rainfall and other data, rather than arbitrarily doing it." Thickness considers plant type. For example, in a soil layer with a thickness of 40 cm, you can choose to plant small shrubs, which can meet the needs of root growth. The trees need a soil layer thickness of at least 70 cm. Secondly, in order to reduce human disturbance, the plant material should have good drought tolerance. Third, plants must have developed root systems, strong growth potential, and certain functions such as dust retention. "Finally, the soil matrix type is selected according to the plant species. There are three necessary conditions, light weight, good water permeability, and certain water retention. Only in this way can a scientific planting system for roof greening be formed."

   The recommended list of plants currently appearing in local roof greening technical specifications, or based on the accumulation of materials used in existing projects, or based on the types of landscaping plants, lacks reliable data support. Experts call for simulating roof conditions and conducting plant planting experiments according to the above process, so that the data obtained from this will be more reliable and safer.

  Gao Xiang said that the main component of the roof greening cultivation substrate is light inorganic substrate, so it cannot support the normal growth of most large root plants. Therefore, plants such as sedum, which can survive with little water and nutrients, are widely used in green roofs. In addition, the biggest feature and advantage of sedum is that its pores are not blocked by dust and particles, and they can endure the heavy load brought by dust and particles, which is unmatched by many plants.

Dialectically view maintenance burden and advocate simple greening

   In recent years, the high maintenance cost and cumbersome maintenance work of roof greening have become a major criticism. "The problem of high maintenance cost of roof greening should be viewed dialectically." Tan Yifan analyzed as an example, the maintenance cost per square meter of ground greening occupying valuable land resources in the central area of ​​the city is 20 yuan, while the cost of land occupation is zero per square meter of roof greening. The maintenance cost per square meter is 30 yuan. "In terms of unit price, roof greening does not prevail, but its functions in building energy saving and prolonging the life of building roofs are very important." He emphasized that there is no saving and efficient practice in reality, so foreign The experience is to develop simple green roofs with low maintenance and low water consumption.

  Gao Xiang believes that problems such as high maintenance costs and cumbersome maintenance work are mainly caused by garden-style roof greening projects. "Garden-style roof greening requires a combination of trees, shrubs, flowers, and grass to create a high-value landscape. These plants require manual professional maintenance, and the cost is naturally not low. And many people ignore a key issue. This maintenance cost is likely to be Much more than the energy-saving benefits generated by the project, such an approach of putting the cart before the horse is worth rethinking.”

In Chicago, Boston and other areas in the United States, the local government believes that garden-style roof greening is suitable for private buildings and commercial buildings, and is not suitable for large-scale promotion. Therefore, when formulating subsidies and incentive measures, only ecological roof greening is implemented. Subsidies and incentives, so This greening model can be rapidly promoted in North America. In Europe, ecological green roofs also occupy an "absolute advantage".