China's first buildings to feature glass curtain walls will reach the end of their design life in the next few years, prompting experts to call for better maintenance of the structures to prevent accidents.

Glass curtain walls, in which a building's facade is made of sheet glass held in place by framework, began to appear in Chinese blueprints in 1984, and have an average design life of 25 years.

The durability of supporting parts, such as bolts and sealant, is generally 10 to 15 years.

In Shanghai, about 900 of at least 4,000 such buildings are more than 15 years old.

"But that doesn't mean they should be replaced by new ones or demolished immediately," said Lu Jinlong, deputy director of the Shanghai Research Institute of Building Science. "They can be used for some time if regular maintenance is done well."

China builds 70 million square meters of glass curtain walls each year, according to the China Architectural and Industrial Glass Association.

The cost of replacing these could be enormous.

"Who should be responsible for the large sum? The developers or the maintenance companies?" said Li Dexiang, a professor at Tsinghua University's School of Architecture. "The problem is there, but there's no efficient solution yet."

Some buildings with glass facades overseas are still in good condition after 50 or 60 years, thanks to timely maintenance.

"The glass curtain wall of a building in University of Birmingham, in the United Kingdom, has stood since 1966 and is doing well till now," said Ron Fillmore, vice-president of Dow Corning Corp, a maker of the glass for many such buildings worldwide.

But there have been many cases in China of glass curtain walls in high-rises bursting without warning.

In Hangzhou, Zhejiang province, a 20-year-old woman was hit by shards of glass from a window that burst in a glass facade as she walked down the street on July 8. Part of her left leg had to be amputated.

A month later in Yiwu, Zhejiang province, a 20-meter-high glass ceiling in a garment market came crashing down, injuring several children, one seriously.

Shanghai enacted a management regulation for glass curtain wall construction on Feb 1, establishing a fund collected from developers and owners of such properties for maintaining and repairing glass curtain walls.

"However, there's a long way to go between setting up the fund and using it to have the glass curtains in good condition in Shanghai," said Lu, of the building research institute. "Let alone in other cities, which don't have such a regulation or plans."

China released a building code for glass curtain walls in 2003, but no guidelines have been issued on who is responsible for the maintenance.

According to Motian City magazine, there were 350 buildings higher than 152 meters, and another 287 under construction on the Chinese mainland in March.

"The number of completed super high-rises may increase by 10 percent this year," said Wu Chengtao, the magazine's editor-in-chief.

"But the construction of many glass curtain wall buildings takes only the charming exterior into account," he said.

"First, they invest more than hundreds of millions in the construction. The cost for later repair and maintenance comes to no small sum," Wu said.