San Francisco's Millennium Tower may no longer be 645 feet tall and its residents are not happy. The massive residential tower catering to San Francisco’s wealthiest is sinking into the ground.

Millennium Partners, developer of the 58-story tower, informed the homeowners association that the settling (sinking and tilting) of the tower was more than was originally expected, reports the San Francisco Business Times. The residents are hiring engineers to begin their own investigation into the causes.

The developer noted heavy construction in the Transbay Transit Center (which involves underground construction work) has caused the Millennium Tower to settle 16 inches so far. Millennium Tower was expected to sink by 12 inches over its entire lifetime.

The tower’s homeowners association sent the Transbay Joint Powers Authority damage claims alleging that heavy construction weakened the ground, resulting in the excessive sinking, according to Curbed. The TJPA pushed back against claims it was responsible, blaming the developer and calling the building’s concrete structure too heavy and foundation too weak.

“Full responsibility for the tilting and excessive settlement of the building lies with Millennium Partners, the developer of the Tower,” reads the TJPA statement. It offered comparisons with similar projects in the vicinity, such as Salesforce Tower, which it states invested in stronger foundations and do not seem to suffer from these problems.