Nature and Gravity: 1.
I wonder how USGBC will want this little problem factored into the building's life-cycle cost savings? Y'know, all that jack they promise building 'green' will save the Owner?
As an architect, I actually like the idea of 'green roofs', and have since the 70's when I first read about the designs of architect Malcolm Wells. (Back then it was called 'earth sheltered' -ed.) I found the idea of earth sheltering compelling aesthetically, and still do. But nowadays the goal of a green roof' is all about the political, not aesthetic or functional.