While a demolition contractor clears debris and stabilizes the site of what the owner claimed was the largest sloped green roof in North America, a forensics team is investigating why the structure suddenly collapsed on the afternoon of Feb. 13.

Roof collapse, St. Charles, Ill., snow, ice, green roof, Aquascape, structural collapse
Photo: Courtesy Aquascape
Freeze-thaw cycle following major snowfall apparently triggered collapse of large green roof near Chicago.

The 700-ft by 50-ft area of roof that collapsed was attached to a warehouse. There were no injuries or inventory damage, said Ed Beaulieu, vice president at Aquascape, a garden pond construction and supply company headquartered in St. Charles, Ill.

“It happened on Sunday afternoon at 3:30 p.m. when no one was there—a good thing since normally cars and people are coming in and out of the garage,” he says.

The collapse likely resulted from an ice dam at the base of the roof that prevented drainage of snow melting over the parking structure, according to a company press release.

The collapse occurred at the beginning of a warming trend following a severe snow storm, Beaulieu says. On February 1-2, St. Charles received 20.6 inches of snowfall in less than 24 hours accompanied by freezing temperatures and followed by temperatures in the 40 degree F range that caused a quick thaw, he recalls.

A team of investigators, including local building inspectors and structural engineers from Texas, has been on site for the past few days, taking pictures and gathering information for analysis, Beaulieu says. Robinette Demolition, Oakbrook Terrace, Ill., is shoring up and stabilizing the building before the forensics team completes its work.

The firm did not remove any snow from the roof prior to the collapse, Beaulieu says. The green roof was planted with native Illinois prairie plants in six inches of soil, he says.

“We couldn’t estimate how much snow accumulated since we couldn’t see the roof,” he says. Due to the unique wedge shape of the building, the top of the roof is only visible from a development south of the building, Beaulieu says.

The 260,000-sq-ft building has a 770-ft-long sloping roof that slopes upward from the parking garage where the collapse occurred, Beaulieu says. The roof experienced no problems during several other recent rain events, including one with about eight inches of rain in 24 hours—a 100-year storm event—and tornado-level winds that took down a building across the street, he says.

Aquascape’s building, completed in 2005,was designed by Artisan Design Build in Monroe, Wisc. and Tricon in Dubuque, Iowa was general contractor.

Beaulieu arrived at the collapse at 5 p.m. after receiving a call from the fire department. “I was shocked,” he says. “It never entered my mind that something like this would ever happen.”

Aquascape is searching for a temporary facility where its 100 employees can work during reconstruction, Beaulieu says.