[The place to go for information about the energy and emissions impact of buildings in the overall scheme is Ed Mazria's Architecture 2030. Other articles on Post Carbon Cities that have to do with greening existing buildings:
http://postcarboncities.net/node/185
http://postcarboncities.net/node/1439
http://postcarboncities.net/node/2287

This article EXCERPTED: read the complete article here. -Ed.]

By Amy Cortese

Just about every month, a glitzy tower rises somewhere in the country, boasting the latest in "green" design and technology. To many people, that is an encouraging trend, especially when considering that commercial buildings account for more than 60 percent of the nation’s electricity consumption, according to government estimates, and generate 30 percent of all greenhouse gas emissions.

Yet these buildings represent a small fraction of the nation’s estimated 4.5 million commercial properties, many of which were erected decades ago before sustainable, or green, designs became de rigueur. This vast stock of older buildings presents a much bigger opportunity to cut down on energy consumption and carbon emissions that contribute to the warming of the planet.

The real estate industry has recently begun to turn its attention to "greening" existing buildings. The United States Green Building Council — whose Leadership in Energy and Environment Design, or LEED, program has become the de facto standard for sustainable building — has guidelines that address older buildings. Called LEED for Existing Buildings, or LEED-EB, the three-year-old program provides a laundry list of steps that building owners and managers can take to operate and manage their properties more efficiently.

"With an existing building, you have to make the most of what you’ve got," said Doug Gatlin, the vice president for market development at the Green Building Council. "We recognized that most buildings are not going to go through a gut rehab," he said, adding that there were basic actions building managers could take to greatly improve a building’s energy efficiency and effect on the environment.

Like the certification program for new buildings, the program for existing buildings assigns points for various steps, including efforts in recycling, water and energy efficiency and air quality. (If a building will be more than half vacant during a renovation, the council considers it new construction.) There are four levels of certification, from basic to platinum, which is awarded to the highest-scoring buildings.

...

LEED-EB is just gathering steam in the broader market. "We’re seeing a lot of companies that want to be LEED-certified across their portfolios," [Doug] Gatlin [vice president for market development at the Green Building Council] said. The council is working with 40 or so big companies — including CB Richard Ellis, Cushman & Wakefield and corporations like Citigroup, to apply LEED standards across their buildings, he said.

Photo credit: Seth Gaines
The Jean Vollum Natural Capital Center is a Portland landmark; originally built in 1895, it was renovated to the LEED Gold standard in 1998.