Green roofs, which is to say roofs covered in part or completely by vegetation in a growing medium, are extremely cool. Not only do they look fantastic and reduce energy bills, but they also offer valuable habitat for migrating and resident birds. So why don’t we have more? After watching this short video about green roofs in NYC, I’m looking forward to seeing a lot more urban roofspace converted to greenspace. Does anyone know why this isn’t already happening on a massive scale?