Chicago City Hall’s Green Roof
Two commercial “green” roofs have been in the news this week. One involves a collapse; one involves energy savings.
Green Roof Collapse
The green roof at the Aquascape, Inc. warehouse in Illinois collapsed over the weekend, likely due to melting snow and ice. A 50 foot wide section of th 256,000-square-foot roof (allegedly the largest sloping green roof in North America) collapsed on Sunday, although no injuries were reported. A team of structural engineers from the building’s design firm is investigating the cause. As noted in a company press release, St. Charles, IL, where Aquascape Inc’s head office is located, had been recently hit with a major snow storm where 20.6 inches of snow had fallen in less than 24 hours, followed by above freezing temperatures causing a quick thaw. An ice damn at the base is suspected to have backed the water up over the parking structure causing its collapse.
Solar Roof goes “live”
While Aquascape’s engineers are investigating their roof collapse, there is some good green roof news closer to home. Raleigh-based marble company David Allen Company has recently “flipped the switch” on a photovoltaic solar energy facility that it claims is one of the largest rooftop photovoltaic systems in the Triangle, with 700 solar modules covering 23,000 square feet of the rooftop of the company’s warehouse. The company hopes to offset at least 35% of its current electrical costs, and sell energy to Progress Energy as well, according to Triangle Business Journal.
Legal Implications related to Roof Design?
Both of these roofs bring up legal issues. Was the Aquascape green roof designed appropriately to accommodate loads in a winter climate?
With so many roof collapses this winter (including, of course, the Minneapolis metrodome) , is there, or should there be, a duty on the building’s owner/maintenance crew to proactively remove snow accumulations?
For new solar roofs, such as at David Allen Company, who assumes the risk if the expected cost savings are not realized?
Based on the sheer number of roof collapses this winter, and the number of green projects growing steadily, there is sure to be some litigation addressing at least some of these issues in the near future. Stay tuned.
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Thanks for this very informative post Melissa. No question about how a lot of households are into green roofing now. But whats alarming is the a number of recent green roof collapses in winter.
Thanks for the comment. Yes, the idea of a roof collapse is not an appealing one!
I’m guessing using the snowblower on my roof is out of the question.
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It’s important to note the fact that the portion of the green roof that collapsed was not on the building but was a canopy extending 60 feet out from the building. The building roof didn’t show any damage at all.
This is an unusual situation, the vast majority of green roofs are directly over a structure. This is a also a very large canopy some 500 x 60 feet.
This is a sloped roof and Chicago had 20+ inches of snow, which subsequently, quickly melted. This could have led to the ice dam referred to in the news stories. Because this portion of the roof was not over the structure, it would have a different freeze thaw cycle, which might have contributed to considerable extra weight.
What we should learn from this is that any time there is anything different or out of the ordinary about a green roof (or any constructing element) it’s necessary to pay particular attention to the structural aspects of the design.
The first thing any good green roof designer or contractor does is make sure a structural engineer is completely involved with the project. And when there is an unusual element to the project, he/she needs to be involved start to finish, not just sign off on preliminary plans
Karen:
Thanks for your detailed comment. I was unaware that the collapsed portion was the canopy only. I definitely agree that a structural engineer needs to be involved during the entire project.
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Thanks for the comment, Chris. At some point green may be just another given, with insurance products the norm, but for now it definitely merits close attention.
Great post Melissa. This just points out some of the risks related to some of the laudable “Green” technologies out there. It also points out the need to assure that the contracts in place for a project properly allocate the risks.