Don't laugh just yet - I hear this comment often! And its true, vegetated roofs have a mind of their own. But today I am writing because I was meeting with one of the professors at one of the universities last week. We were discussing a stormwater research project. Near the end of the meeting the conversation turned to the many BMPs referred to in the proposed new Florida stormwater rule, one being Green Roofs.
The professor, with humor in his/her voice, spoke of the green roof project the university architect designed and how after installation the roof looked beautiful.
Continuing, the professor added that the roof had changed so much over the past year that most associated with the project were shocked.
I've seen this occur on every vegetated roof here in the Southeast US. The maxim is: Unless you have an endless budget for maintenance and unlimited time to work with the roof, expect change.
Through design you can minimize the change but you should still expect change.
The winds, rain and birds bring seed material. New aggressive pioneer species pop up right and left. The harsh environment knocks back the carefully tended to plants installed during the initial planting. Harsh winds desiccate some of the plants. Others wilt or develop dampening off with the high heat and humidity. A vegetated roof generally has a mind of its own and you must ask if you have the time and energy to fight.
Again, I remind all I am speaking from a Florida and humid Southeastern US perspective. Green roofs may behave different up north, I do not know.
So, I smile when I hear someone say, usually while shaking their head, that a vegetated roof has turned into something they did not expect.
We are compiling a database of plants suited for Southeastern US roofs and will be posting before the end of the year - would love your feedback.
Happy Green Roofing!