Willis Tower Windows Broken By Rooftop Pebbles, Officials Say

06/22/2010 11:01 am ET | Updated May 25, 2011

CHICAGO — Chicago officials say white pebbles spread on rooftops to reflect sunlight are to blame for some broken high-rise windows in last week's violent storms.

The white pebbles are put on roofs to lessen the need for air conditioning in the buildings.

Jose Santiago, director of Chicago's Office of Emergency Management, said Monday that the 77 mph winds that hit the city Friday afternoon picked up an unusual number of the pebbles and pelted them against windows.

One of the buildings where windows were broken was the 110-story Willis Tower, long known as the Sears Tower.

Two windows in the imposing black building were broken.