How do you make an old building green?

But as engineering vice-president at Merchandise Mart Properties, he has just finished a three-year, multimillion-dollar odyssey to cut the massive structure’s consumption of energy, water, and materials. The effort required overhauling decades-old practices and technology, from replacing most of the Mart’s 4,000-plus windows and upgrading rusty motors deep in its subbasements to taking better care of dust mops. The reward: At 78 years of age, the Merchandise Mart is now the biggest green building in the world.

BusinessWeek examines the process of making the Merch Mart LEED-certified with the help of the Delta Institute. Via Coudal.