The sudden crack in a 36th floor window at San Francisco's Millennium Tower has been determined to be caused by "exterior impact," according to an investigation report from the Millennium Tower Association.
The report conducted by Allana Buick & Bers, a consultant hired by the homeowners association, also concludes the cracked window "is unrelated to building movement and settlement."
City officials recently declared the luxury high rise safe after investigating the cracked window. The window in unit 36B suddenly failed on Sept. 1, forcing the building to be surrounded by scaffolding to protect pedestrians.
A consultant’s preliminary report suggested the window failure could be the result of the tower’s tilting triggering separation of the outer façade, or curtain wall, from the concrete framework of the building. That problem was highlighted earlier this year, when NBC Bay Area reported how Paula Pretlow, who owns unit 31B, had learned that a consultant worried about the risk caused by gaps they found inside her walls – between the glass and steel façade of her unit and the concrete interior structure.