Millennium Tower Sinking: Causes, Settlement, and the Fix

San Francisco’s Millennium Tower, a 58-story luxury condominium at 301 Mission Street, has been sinking and tilting since before it opened in 2009 because its foundation was built on friction piles driven into sand rather than anchored to bedrock. The problem produced roughly $500 million in settlements, a $120 million engineering fix completed in September 2023, and steep losses in unit values that residents are still absorbing.¹

Why the Tower Started Sinking

The 645-foot building sits on a 10-foot-thick concrete mat supported by roughly 950 precast concrete piles driven about 80 to 90 feet down into a layer of dense sand. Bedrock lies more than 200 feet below street level, and the piles were never extended to it. They were designed to carry the tower’s weight through friction with the surrounding soil.²¹

Below that sand lies a thick deposit of compressible marine clay called Old Bay Clay, running from roughly 90 to 220 feet down. Under the tower’s weight, the clay began to squeeze out water and consolidate. The original geotechnical analysis had predicted just one to four inches of settlement over the entire lifetime of the building. The clay compressed far more than that.²

A second factor was contested throughout the litigation. Engineers for the homeowners’ association alleged that construction of the neighboring Salesforce Transit Center dropped groundwater levels by as much as 20 feet, reducing the buoyancy holding the tower up and increasing the effective load pressing down on the clay. Repeated dewatering episodes at the tower’s site and adjacent sites between 2006 and 2018 compounded the problem, and deep excavations next door caused lateral soil movement that contributed to the tilt.³ The Transbay Joint Powers Authority, which oversaw the transit center, denied responsibility.⁴ The HOA’s engineers went further, calling the original foundation design “inadequate to support dead and live loads.”¹

How Far It Sank Before Anyone Was Told

The tower was already in trouble before residents moved in. By 2009, an investigation tied to the neighboring transit center found the building had sunk 10 inches, four inches beyond the total settlement predicted for its entire life. A February 2009 letter from a San Francisco Department of Building Inspection official raised questions about the sinking. The DBI certified the building for occupancy anyway that August.⁵⁶

An independent safety review in 2014 concluded the sinking posed no immediate safety risk. Then in June 2015, tenants learned the tower had sunk 16 inches and was tilting several inches to the northwest. By 2016, the European Space Agency estimated the building was dropping about two inches per year.⁵ Residents later alleged that developer Millennium Partners had known about the excessive sinking as early as 2008 and failed to disclose it to buyers.⁷

The Lawsuits and the $500 Million Settlement

By late 2017, roughly 20 parties had filed claims arising from the tower. Residents brought a class action in San Francisco Superior Court in August 2016 against Millennium Partners, alleging the developer knew about the sinking before selling units. San Francisco City Attorney Dennis Herrera filed a separate fraud suit that November.⁷⁸

In March 2017, the Millennium Tower Association filed its own suit against the developer, contractors, engineers, architects, and the TJPA, seeking more than $200 million and alleging both nondisclosure of known defects and damage caused by transit center construction. Webcor Builders, the tower’s general contractor, was among the defendants.⁸⁹

In August 2019, the parties reached a tentative global settlement valued at roughly $500 million, resolving claims by 418 of the tower’s 419 unit owners against Millennium Partners, the TJPA, builders, consultants, and representatives of neighboring buildings. The deal funded a $100 million perimeter pile upgrade and paid individual “stigma payments” to homeowners for the loss in property value tied to the tower’s publicity. Specific individual figures stayed confidential.¹⁰ The TJPA was expected to pay a substantial portion while continuing to deny that its construction caused the movement.⁴ The class action received final court approval on August 7, 2020, and the global settlement was confirmed final and effective on October 7, 2020. All claims against the TJPA were dismissed with prejudice.¹¹

The Engineering Fix

Simpson Gumpertz & Heger, led by structural engineer Ronald Hamburger, designed the retrofit. The original plan called for 52 piles drilled to bedrock. After early pile installations caused the tower to sink an additional inch, construction was halted and the design was overhauled.¹²

The revised design used 18 large piles, each capable of carrying one million pounds, installed along the Mission and Fremont Street sides where the tilt was most severe. Each was drilled roughly 275 to 300 feet to bedrock using double-cased, cast-in-place construction with friction-reducing coatings and structural fuses meant to protect the existing foundation. Hydraulic jacks then transferred approximately 18 million pounds, about 10% of the building’s total weight, from the failing friction piles onto the new bedrock-anchored supports. All 18 piles were jacked simultaneously in 100,000-pound increments with real-time monitoring. Shimmick’s Legacy Foundations served as the contractor.¹³¹⁴

The reduction from 52 to 18 piles drew criticism. San Francisco Supervisor Aaron Peskin questioned why the original scope was not better calibrated, and independent geotechnical engineer Robert Pyke suggested the design team was “panicking because they’re out of time and money provided by the settlement agreements.” Peskin also called the cure “a lot worse than the disease” given the extra settlement the early construction triggered.¹⁵

Construction finished in September 2023 at a final cost of about $120 million. Residents remained in the building throughout the two-year job, and the project requires ten years of monitoring.¹

Did It Work?

The results are mixed. In June 2023, the project team declared that settlement had been arrested along the north and west sides, and city officials announced the tower had stopped sinking and tilting.¹⁶ By early 2024, monitoring showed the building had recovered roughly one inch of its nearly 29-inch northwest tilt.¹⁷

That one inch was only about a quarter of what the engineering model had predicted. Monitoring data also show the tower’s center is still settling at roughly a tenth of an inch per year, a pattern engineers call “dishing.” Foundation expert Harry Poulos noted that while the rate is not large, it is “not heading in the right direction.” Pyke warned the dishing could crack the underside of the foundation, letting water reach and corrode the steel reinforcement inside. Pyke has also suggested that a buried wall under the east side of the foundation, meant to separate the tower from an underground garage, may be preventing the expected tilt correction by carrying weight the model assumed would shift. Hamburger has maintained that the “remainder of the building continues to settle as we always anticipated.”¹⁷

City-appointed technical experts had already concluded in July 2017 that the settlement and lean “have not compromised the building’s ability to resist strong earthquakes and have not had a significant effect on the building’s safety.” The piles retained sufficient compressive and tensile strength to resist forces from a maximum considered earthquake.² After the fix was completed, the DBI approved the foundation stabilization and a voluntary seismic upgrade as code-compliant.¹⁸

Cost Overruns Passed to Residents

The HOA had been allotted $150 million from the settlement to cover the retrofit, legal bills, and reserve restoration, funded in part by the compensation homeowners received for lost property value. Overruns of roughly $20 million strained that budget. The developer and contractor contributed $10 million toward the excess, leaving a $6.8 million gap. The HOA levied an emergency assessment of $10 per square foot of condo space, due October 1, 2023.¹⁹

Owners were furious. Mehrdad Mostafavi, who had vacated his unit because of sewage backup caused by the building’s tilt, said he had already spent his retirement savings on separate repairs and “cannot accept paying even more money.”¹⁹

What It Did to Unit Values

Prices in the building collapsed. A unit that sold for $1.5 million in 2015 was later listed for $800,000, a 47% drop. Another that originally sold for $1.1 million was listed a decade later for $649,000, a 41% decline. Two-bedroom units set record lows of $650,000 in 2023 and $800,000 in 2024.²⁰

The Grand Penthouse, bought in 2016 for $13 million, was listed for $14 million in May 2023 and sold for $9 million in January 2025. Realtor Gregg Lynn called it the highest resale of a downtown San Francisco condo since 2018, and the buyers’ ability to secure a $5 million mortgage was cited as a sign lenders will again finance units in the building. As of mid-2026, seven units were publicly listed, ranging from $650,000 to about $5 million.¹⁸

The Regulatory Failure

The Department of Building Inspection knew something was wrong long before the public did. DBI officials later testified there was a “buzz” within the department as early as 2009 that the tower was sinking more than forecast, yet no public action followed for seven years. Former deputy director Raymond Lui said that after receiving a response from the developer’s engineers, the department “felt that they had it under control.” The agency relied entirely on assurances from the developer’s paid consultants, a practice assistant director Ron Tom later said “is not going to continue.”⁶

The DBI did not open a formal investigation until August 2016, after an anonymous 311 complaint, 15 days after the sinking became public through media reports. The department also failed to keep key documents, including a January 2009 developer letter admitting the tower had already sunk more than eight inches. Peskin said he was “rather shocked” the DBI’s records retention policy “had not been brought into the dawn of the 21st century,” and the Board of Supervisors later approved a code change requiring the city to retain all documents generated after building permits are issued.⁶²¹

1
Simpson Gumpertz & Heger. Millennium Tower
2
City and County of San Francisco. Millennium Tower Safety Review Report
3
ASCE Library. Millennium Tower Settlement and Tilt
4
San Francisco Chronicle. Settlement Reached in Millennium Tower Suits
5
Business Insider. Millennium Tower San Francisco Tilting Sinking Timeline
6
San Francisco Examiner. SF Building Inspectors May Have Known of Millennium Tower Issues Since 2009
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ABC7 News. Timeline: Issues With SF’s Tilting, Sinking, Cracking Millennium Tower
8
Forbes. Legal Headache Becoming Migraine for Millennium Tower’s Developers, Homeowners
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Bloomberg Law. Zurich Beats American Financial Unit in Millennium Tower Lawsuit
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NBC Bay Area. Parties Reach Half-Billion Dollar Global Settlement in Legal Fight Over Sinking Millennium Tower
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Jones Day. TJPA Reaches Global Settlement in Millennium Tower Litigation
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NBC Bay Area. San Francisco Millennium Tower Fix
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Engineering News-Record. Project of the Year Finalist: 301 Mission Perimeter Pile Upgrade
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Engineering News-Record. Millennium Tower
15
ABC7 News. Millennium Tower San Francisco Sinking Fixing
16
San Francisco Examiner. SF Millennium Tower Stopped Sinking, Building Officials Say
17
NBC Bay Area. San Francisco Millennium Tower Foundation Sinking
18
KTVU. SF Luxury Millennium Tower Penthouse Sells for $9M, Millions Less Than Original Asking Price
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NBC Bay Area. Millennium Tower Residents Billed for Fix
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SFGate. Millennium Tower San Francisco Price Drop
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NBC Bay Area. Document Retention Reforms Inspired by Millennium Tower Debacle Move Forward