Okay, we may be jumping the gun on this one, as the Bullitt Center isn't slated for completion until this fall. But when you lay claim to the title of the world’s greenest, most energy efficient commercial building before the doors even open, you'd better have your ducks in a line. The Bullitt Center in Seattle -- the headquarters of the Bullitt Foundation, a non-profit dedicated to safeguarding the natural environment of the Pacific Northwest -- will be the largest structure ever built to the ultra-green standards of the Living Buildings Challenge. This building standard, appropriately enough, was developed by the Cascadia Green Building Council, which is also based in Seattle -- it mandates (among other things) net zero energy usage and on-site sewage treatment. That means that staff members and visitors to this six-story, 50,000-square-foot building going up at the intersection of Seattleʼs Central Area and Capitol Hill neighborhoods will have to take the stairs, and get used to composting toilets. The building was meant to serve as a “living laboratory” for cutting-edge sustainable building technologies and practices.