Feature image:
![Source: Serge Melki, via Flickr](http://new.usgbc.org/sites/default/files/treasury.jpg?1347379338)
I’m thinking of a Federal building. It is the third oldest federal building in our Nation’s capital. It houses the Federal department in charge of promoting economic growth. And, thanks to a green retrofit, it saves American taxpayers $3.5 million every year.