Heavy Falls of Hail and Rain Leading to Roof Collapse

The operation of two large and dense weather networks to record and measure rainfall and hailfalls in two urban areas have yielded interesting weather-damage information that may need to be considered in certain structural designs. The Illinois State Water Survey operated a network of 250 hail sensors and recordings raingages in a 2,000-sq mile area surrounding St. Louis during the 1971-1975 period in a study to learn how cities affect the weather with special attention to effects on rainfall. The survey also initiated a multiyear project to study rainfall and hail distribution in the Chicago region with 300 recording raingages and hail sensors in a 4,000-sq mile area. The data from these networks give unique information on the time and space occurrences of rainfall and hailfall rates and amounts. During the operation of these networks two instances of roof collapse have come to our attention without any special efforts to collect such information. Quite possibly, more such roof failures occurred and we were not aware of the occurrences.