France has recently passed a law decreeing that all new buildings in commercial zones must have roofs partially covered in either plants or solar panels.

This follows Toronto's 2009 bylaw requiring green roofs on new commercial, institutional, and many new residential buildings.

Green roofs help save energy by heating buildings in the winter and cooling them in the summer, as well as filtering air pollution and mitigating urban noise. 

This is a narrowed version of a law which activists had originally called for, green roofs on the entirety of all buildings.