Leaning Millennium Tower in San Francisco sinking faster, retrofit halted

A retrofit of the leaning Millennium Tower of San Francisco has been suspended after crews discovered the building was sinking at a faster rate during the construction effort.

The nearly $100-million retrofit was halted Aug. 19, and a two- to four-week moratorium was announced “while we try to understand better the mechanisms associated with the increased settlement rate and available means of mitigating this,” Doug Elmets, a spokesman for the luxury residential building’s homeowners association, said in an email.

“There has been no material harm to the building and it remains fully safe,” Elmets said. KNTV-TV first reported on the suspension of the retrofit project.

One of San Francisco’s tallest skyscrapers, Millennium Tower has sunk since construction began in 2006 and is tilting. The building is ranked as San Francisco’s sixth tallest building, according to skyscrapercenter.com.

Millennium Tower is in the heart of San Francisco’s South-of-Market district, which has transformed over the last two decades from a forgotten part of downtown to a capital of tech money in the city. Just next to Millennium Tower is Salesforce Tower, the tallest building in San Francisco, as is Salesforce Transit Center, an elaborate bus terminal that will someday connect to Caltrain service to Silicon Valley.

A problem for Millennium Tower, some structural engineers have said, is that its foundation reaches only to a layer of sand, just above a layer of clay, instead of farther down into bedrock.

Such a construction practice was common in this part of San Francisco, where the bedrock is quite deep underneath thick layers of soft soil, sand and clay — but that was for buildings that were much shorter and lighter than Millennium Tower.

In October, the homeowners association, Millennium Tower Assn., announced plans for the engineered retrofit of Millennium Tower to “prevent any significant future settlement of the skyscraper.” The plan involved installing 52 concrete piles — or columns — that would anchor the building to bedrock, 250 feet below ground.

In October, the association said that Millennium Tower’s tilting and sinking had virtually halted over the prior two years. “The engineering retrofit will provide long-term assurance of the tower’s performance in the event of any future construction nearby and will potentially reverse a significant portion of its tilt,” the association said in October.

Millennium Tower was developed by New York-based Millennium Partners, which sold off the residential units to people who bought condo units in the building.

Millennium Partners is attempting to build another skyscraper project in Hollywood, a project that has come under criticism after state geology officials have said there are studies that “strongly support the presence of an active ... fault strand entering” the skyscraper site.

Millennium Partners and Los Angeles City Hall have previously rejected the state’s concerns and insisted that the skyscrapers were safe to build. More seismic studies have been ordered for the Hollywood Center site.

Opponents of the developer’s Hollywood Center project said the ongoing problems with Millennium Tower in San Francisco should be a warning sign to Los Angeles to not allow Millennium’s Hollywood project to proceed.

“The ongoing disaster in San Francisco is more evidence that developer Millennium Partners cannot and should not be trusted,” said Robert P. Silverstein, a Pasadena lawyer who represents neighborhood groups opposed to the development.

Millennium Partners declined to comment.