By Jorg Breuning
As of late we have been receiving more and more calls from building owners in distress about their green roofs. The most serious of these complaints being erosion problems on their sloped roofs. Sloped green roofs are a bit more complicated to design, install, and maintain than flat roofs and as a result people who disregard or don't know of the established FLL guidelines for sloped roofs, have created dangerous and costly situations ranging from mudslides to roof collapse.
One of the most infamous of these rooftop blunders was last winter in St. Charles, Illinois. The project was designed to be the largest sloped roof in the US and during a heavy snow storm the roof collapsed. Fortunately no one was hurt however the damage was devastating.
Why did the roof collapse? The problem lies in the drainage. Snow is frozen water and where you have more water accumulating on a roof you will also have greater amounts of snow accumulate. This insufficient or clogged drainage system and poor growing media is the most likely culprit in areas that held water or snow. All this added weight during an extreme winter put the roof way beyond its capacity.
Sadly, this situation and others like it could have been avoid simply by hiring a true expert and checking their performance history for similar projects. To read more about the dangers of improperly design sloped extensive green roofs and how to avoid them click here.
Below the renovated roof after it collapsed. Suddenly the green portion shrinked by at least 1/4.