Allana Buick & Bers, a forensic engineer hired by the Millennium Tower Association, says the cracked window glass in Unit 36B of the San Francisco residential building was caused by an exterior impact. The glass damage, which occurred Sept. 1, is “unrelated to building movement and settlement,” says an Oct. 2 letter from the condominium owner’s association to the city’s Dept. of Building Inspection. ABB, which studied the exterior from October 2016 through February and again in September, said there is no need for further investigation of the curtain wall. The 58-story tower—the tallest reinforced concrete structure in the western U.S.—has settled 18 in. and tilted 2 in. since its completion in 2009.