What's an ecoroof you ask?
It's a vegetated rooftop achieved through planting carefully selected vegetation in specially designed soil layered over drainage material, all atop a conventional roofing membrane. It costs more than a traditional roof, but has many other benefits...triples roof life, reduces runoff, saves energy, absorbs carbon dioxide, gives off oxygen, etc. etc.
And it's going up atop Portland's Central Library. Tours of the library’s new roof may be offered to the public once the project is completed, said John Cabrera, a spokesman for the library.