Many high-profile tenants won't even consider moving into a property without the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) certification, said Allan Skodowski with Transwestern management group. They may not even know what the certification means, he said, but they demand it nonetheless.

"They say 'We want LEED,'" Skodowski said, "and that's it."

Nine of Transwestern's properties received certification this year. A combination of energy efficient light bulbs and other green equipment helped those buildings slash energy consumption. On average, they've seen a 2 percent drop in energy costs, even as electricity rates jumped between 10 percent and 40 percent, Skodowski said.

Leasing rates have not risen as a result of the changes, Skodowski said, yet at the same time occupancy rates have not fallen. That's a victory for an industry hit hard by the recession. Vacancy rates at office buildings nationwide have gone from 10.9 percent at the end of 2007 to 12.4 percent in the first quarter of this year.

"If one extra tenant comes and looks at the building, if the owner gets an extra penny or so a foot, then at the end of the day it's paying for itself," Skodowski said.

A recent analysis by real estate researcher CoStar Group, Inc. found that green-certified buildings had fewer vacancies than other buildings with similar age, size and location.

The CoStar study, which included about 3,000 green-certified offices, found that buildings with the council's certification enjoyed higher occupancy rates (90.3 percent) than their peers (84.7 percent) in the first three months of 2009.

Certified buildings have fetched higher lease rates for several years. The CoStar report said the buildings rented at an average of $38.86 per square foot in the first quarter of 2009 compared with $29.80 per square foot for their peers.

"This isn't just a 'We are doing the right thing' movement," said Marc Heisterkamp, U.S. Green Building Council's director of commercial real estate. "In the end, the numbers pencil out."

At the Empire State Building, Malkin proposed a top-to-bottom renovation that included a $13.2 million investment in new green technologies. The goal was to sufficiently reduce greenhouse gases without spending more than he could justify to his investors.

What the owners settled on was a series of upgrades that include retrofitting all 6,500 windows. Under every window, radiators will be padded with extra insulation. The building's lighting, cold water and ventilation systems also will be upgraded.

The renovation should take 18 months. Afterward, the owners expect an annual energy savings of $4.4 million, enough to pay off the new technologies in about three years.