Aquascape's head office had "the largest sloping green roof in North America, planted with native prairie grass and flowers and a complete irrigation system." Who would think that a firm that makes water gardens could be so big, to have a quarter of a million square feet under that roof. Jetson Green described it as a "virtual prairie meadow in the sky."
Last Sunday, a section of it collapsed; the company says it "was likely the result of an ice dam that prevented water from the rapidly melting snow from draining off the roof."
See photo of the collapsed roof in the Chicago Tribune here
Green roof fans quickly responded in support of the concept. From the Tribune:
"There's really nothing about the inherent design of a green roof that should make it more susceptible to this kind of collapse," said Joseph Clair, director of energy and sustainability at the Illinois Institute of Technology. "Green roofs have been installed in this country and other countries that have snow for hundreds of years."
Sloping green roofs are also probably even safer than flat ones, as there is less worry about drains clogging. But if there is a roof overhang or an unheated area (part of the green roof went over a parking garage) then water can build up behind the dam and cause a lot of damage. We don't know exactly what happened here; (the VP of the company says "I honestly don't think we can make that assessment yet. I do know that the structural members were greatly increased over what would be used in a standard building.")
But a lot of green roof architects and engineers will be watching very closely.
More in the Chicago Tribune