With today’s focus on “green” buildings, it’s no wonder that so many of the new towers scraping the Chicago sky are heralded for their benign impact on the environment. But what about the thousands of other high-rises and humbler structures already here?

 

Improving the energy profile of older buildings is a much harder feat. Before virtuous materials and systems can be installed, the old stuff has to be ripped out and hauled off. Managers of existing buildings also have to keep operations humming so as not to disrupt rent-paying tenants.

 

“It can be like performing surgery while the patient is still awake,” says Mark Bettin. Bettin has never performed in an operating room. 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 sub-basements 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.

 

It’s hard to overstate the scale of this undertaking. Straddling two full blocks and reaching up 24 stories, the complex contains 4.2 million square feet—about 400,000 more rentable space than the Sears Tower—and enough to qualify for its own Zip Code (60654).

 

Behind its limestone exterior are 380 miles of electrical wiring and 40 miles of piping and ductwork. The Mart requires 400 employees just to keep the place functioning. With more than 700 tenants, the building’s daytime population numbers 15,000 to 20,000. Every year, 3 million visitors stop in for trade shows and conferences.

 

The new and improved Mart may inspire other building owners to retrofit their properties, in Chicago and elsewhere. Fast-multiplying local and national goals to lower greenhouse gas emissions and energy use are putting existing buildings under greater scrutiny. Commercial buildings consume about 40% of the nation’s energy and generate about the same share of the gases blamed for global warming.

 

Yet new structures, where almost all green construction is happening today, add less than 2% to the total building stock each year. Thus, the only way to hurry along savings is to update the nation’s 4.9 million older commercial structures.

 

The rush to go green isn’t only due to government mandates. If owners of pre-21st century structures want to draw tenants who’ll pay top dollar, their properties must be as inviting as new places. That means installing not only the latest technology, but also green features, such as healthier workspaces stocked with nontoxic furnishings, carpets, and cleaning agents, plus plenty of natural light and ready access to public transportation.

 

Still, upfront expenses — and inertia — often hold landlords back. “Big existing buildings are a great opportunity, but they’re harder to get to,” notes Sadhu A. Johnston, the City of Chicago’s chief environmental officer. “They rarely go through major retrofits, and they’re not coming in for permits, so there just aren’t as many openings for us to point out how to do things differently. They have to go out of their way to go green.”

 

To remake the Mart, Bettin turned to the U.S. Green Building Council in 2005. A nonprofit standards-setting body, the council provides the imprimatur for green real estate, thanks to its Leadership in Engineering & Environmental Design (LEED) designation for new structures and LEED-EB certificate for existing buildings.

 

Think of an application for approval as a multiyear beauty pageant — but instead of points for swimsuits and talent, building managers get points for operational excellence, ranging from how much water they save to how clean they keep the air…