New World Development says two blocks under construction at the Pavilia Farm III residential estate above Tai Wai MTR Station will be demolished and rebuilt after the wall base failed concrete strength tests.
The demolition will cause a nine-month delay to the occupancy date for 846 affected buyers, who can choose to complete the purchases or cancel the transactions immediately with compensation.
There will be 47 to 57 floors in the towers when completed.
The estate is a joint development between New World Development and the Mass Transit Railway Corp.
New World received a report from the project contractor, Hip Seng Group of Companies, on Saturday that it found during an inspection on the same day that the concrete strength in sections of the wall base beneath towers one and eight did not meet design requirements.
Three days later, New World reported the matter to the MTRC and the Buildings Department.
It decided to demolish and rebuild the structures.
New World says it has instructed the contractor to "thoroughly investigate the cause of the incident, including if there was any human negligence and supervisory liability." The developer has also replaced the supervision team of the project.
It is understood more than 10 floors have been built on the towers.
After the problem was found, the developer had considered conducting reinforcement works, instead of tearing down the buildings.
But New World said it wanted to ensure the building quality was good and to provide peace of mind to buyers, and decided to demolish and rebuild the floors that have already been built.
It said the construction quality and structural safety of buildings in the first and second phases of Pavilia Farm meet legal and statutory requirements.
The MTRC said it is highly concerned about the matter and has requested New World submit a full investigation report, as well as to take appropriate follow-up action to ensure the buildings meet the requirements of the approved design, and to take into consideration the interests of affected purchasers.
The MTRC has also requested New World to ascertain the quality of the other towers in the development.
The Buildings Department said it has started an investigation into the incident and requested relevant parties to submit a detailed report.
It will see if there is any contravention of the Buildings Ordinance and appropriate follow-up action will be taken depending on the investigation result.
It also confirmed that there is no obvious danger at the two towers after an inspection on Wednesday, but it has requested that additional testing be conducted on the remaining five towers, where superstructure work was completed, and submit a detailed report to the department.
The department was first notified on June 18 that the strength of the concrete from the core samples taken from the reinforced concrete columns between the seventh and eighth stories of tower eight was lower than the specified grade strength. It then ordered a suspension of superstructure work on tower eight.
On Tuesday, the department received another notification that a similar situation was found in the reinforced concrete load-bearing walls of tower eight and some of the reinforced concrete columns and load-bearing walls of tower one.
So the superstructure work for tower one was also suspended.
Ray Su Kai-leung, an associate professor at the University of Hong Kong's civil engineering department, believed the developer had no choice but to demolish the two towers as the concrete strength problem of the wall base would affect their structural safety
He also said it was difficult to conduct reinforcement works on the buildings as it will reduce the usable area of the buildings.
"Additional support would take up some space. The space beneath is valuable, where it could be used as a car park or driveways," Su said.
He also said the incident is rare as the quality of concrete in Hong Kong is good, and the concrete is ready made at the concrete companies before being transported to the construction site.
Pavilia Farm III, which offers 892 units, has received an overwhelming response from buyers and 666 units have been sold since sales started in early June, bringing in more than HK$9.4 billion.
Phase III of the project also received a record high 30,500 subscriptions when the subscription period ended last month.
Prices for the latest batch of the phase three flats started at HK$7.4 million, or HK$18,760 per square foot.
A first-time home buyer, Lam, who purchased a HK$12 million two-bedroom unit at Pavilia Farm III, said he will not cancel the deal as he tried to buy a flat there in the first and second phases but failed.
He now has to extend the rental period of the Ma On Shan flat he is living in.
Another buyer, Chan, said that she is still worried and demanded the developer provide the findings of its investigation.