The external walls of many high-rise buildings in Shanghai use large-area glass curtain walls. Photo by Zhou Xin
Recently, some readers reported to this newspaper that some glass curtain walls of the World Financial Center reflect strong light. Not long ago, the planned Shanghai Tower, the tallest building in China, published an environmental assessment report online, in which "the influence of reflected light from glass curtain wall" attracted people’s attention.
The glass curtain wall causes strong light reflection and causes light pollution, which has become a problem that cannot be ignored in urban development. Is it a light and beautiful building material "angel" or a "devil" that causes light pollution?
The reporter recently visited the main argumentation and examination and approval department of "light reflection influence".
The inner ring line was once banned, but the effect was not obvious.
In the Building Energy Conservation Section of the Shanghai Construction Industry Management Office and the Office of the Science and Technology Committee of the Shanghai Municipal Construction and Transportation Commission, two responsible persons mentioned one thing in unison-in 1999, the Standing Committee of the Municipal People’s Congress promulgated the Regulations on the Management of Construction Engineering Materials in Shanghai, which stipulated that the Municipal Commission for the Establishment of Diplomatic Relations should compile a "prohibited and restricted catalogue" and publish it after approval by the municipal government.
In 2000, the first batch of "Prohibited and Restricted Catalogue" was published, and the glass curtain wall was among them. At that time, it was clearly stipulated: "It is forbidden to design and use glass curtain walls within the inner ring road, except for the podium of the building; Between the inner ring line and the outer ring line, the area of glass curtain wall shall not exceed 40% of the construction area of the outer wall. Construction projects using glass curtain walls should be implemented after environmental assessment by the environmental protection management department and approval by the planning and construction management departments. "
However, the development of glass curtain wall has not stopped because of the publication of the catalogue. Wu En, deputy director of the Office of the Science and Technology Committee of the Municipal Commission for the Establishment of Diplomatic Relations, explained: "Before the publication of the catalogue, many construction projects have passed the examination and approval. This legitimate reason makes these projects exempt from the catalogue."
At present, there are many glass curtain wall buildings on both sides of the road, many of which were built after 2001 and are within the inner ring. It is forbidden to stop, ostensibly because of the "time difference" of project approval, but in fact it has a compelling reason.
What materials can be used for high-rise buildings without glass curtain walls?
An expert from Shanghai Environmental Monitoring Center, who asked not to be named, believes that the widespread use of glass curtain walls is mainly aimed at the "helpless actions" of the city’s super high-rise buildings. This expert has participated in the examination and approval of many important construction projects in the city. She said that although the regulations on restrictions on the use of glass curtain walls have been issued for many years, it is "unrealistic" to completely ban them. Mr. Shen, the head of the Building Energy Conservation Section of the Shanghai Construction Industry Management Office, said: "The’ one size fits all’ approach is not appropriate."
"The glass curtain wall is really necessary, and some of its advantages are irreplaceable by other building materials." Wu En explained that especially for super-high-rise buildings with more than forty or fifty stories, the load-bearing requirements for the foundation are relatively high. Under the same circumstances, light glass curtain walls have to be used as the external wall. "If a building with a height of one or two hundred meters does not use glass curtain walls, what better materials can it use?"
In addition to being light, the glass curtain wall also has the advantages of beauty, earthquake resistance, high permeability and rapid construction. Since the early 1970s, Shanghai has tried to integrate it into urban architecture for the first time. It has been more than 30 years since then, and its technology has passed the standard and its safety factor is high, which naturally makes it the first choice for many architects and developers.
Light pollution is difficult to avoid, but it must be strictly controlled.
Glass curtain wall is sometimes a "double-edged sword". On the one hand, glass can be recycled, which makes it stand out from many light materials such as aluminum; On the other hand, strong light reflection causes pollution, which attracts more and more attention.
"Admit its necessity, and we can’t ignore the negative effects." Wu En introduced that the municipal environmental protection department has issued regulations that when glass building materials are used for building exterior walls, glass with low reflectivity should be used, and the visible light reflectivity should not exceed 15%.
"The implementation of the regulations is good, but the 15% standard cannot solve the fundamental problem." Yuan Bo, an expert from the Science and Technology Committee of the Municipal Commission for the Establishment of Diplomatic Relations, explained that even if the reflectivity is reduced by half, it will still cause strong light reflection to some extent. "Technically, the ideal reflectivity can be controlled to 3%, but this kind of glass costs three or four thousand yuan per square meter, which is several times that of ordinary glass."
"When the light is sufficient, the glass curtain wall partially reflects a small amount of strong light, which is difficult to avoid. This is not terrible. The key is that it cannot be reflected to nearby residents’ homes and affect their lives. " Wu En introduced that this is what the Science and Technology Committee focused on.
The demonstration is generally divided into two steps: first, draw detailed drawings according to the surrounding conditions of the building, and then analyze the various angles that the glass curtain wall may reflect light, and whether it will affect residents. "When the building is built, it will definitely be too late, and it must be involved when reviewing the construction sketch. If it is not up to standard, the drawing review will not pass. "
"As long as light pollution is found during the demonstration, even if it only affects one or two residents, we will never let it go and must solve it in time." Wu En explained, "There are two commonly used remedies: adding a light shield on the outer wall to reduce continuous total reflection; Stick a film on the glass surface to reduce glare. In the event of a dispute caused by light pollution, it is generally negotiated by both parties, with economic compensation as the mainstay. At present, there is no clear mediation method and compensation provisions. "