HOK and Devrouax +Purnell teamed up to design what could be the first LEED certified Major League Baseball stadium around.* As the new home of the Washington Nationals, the stadium has a slew of green features such as high-efficiency field lighting, a 6300 sf green roof, state-of-the-art wastewater system that uses sand filters, and an in-house recycling center. Originally, architects estimated an extra cost of $10-20 million for certification, but it ended up being only $2 million. Plus, the up-front costs are expected to be returned in lower operating costs. For a frame of reference, though, the owners agreed to spend $611 million for the stadium.