A 15-story, 43-year-old high-rise building in downtown Palo Alto has received one of the highest federal-standard green-building certifications in the country.

Slightly resembling a large waffle, the Palo Alto Office Center, located at 525 University Ave., is the city's largest building. From the outside, it seems an unlikely model for sustainability.

But the towering cement structure recently received the "Existing Building Gold Certification" by the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) Program.

The building is the first in Palo Alto to receive Existing Building, or LEED-EB Gold certification, according to a release by Joyce Kinnear, utility marketing services manager for the City of Palo Alto Utilities' Department.

Several newly constructed Palo Alto buildings have been recognized by the LEED Program. But the office center's achievement is unusual for such an old building, according to Chris Boreta, real estate manager for CB Richard Ellis, Inc., which manages the building.

The 170,640-square-foot building was constructed in 1966 and houses many law firms and financial businesses.

The LEED program rigorously evaluates businesses and buildings in five green-design categories, including water efficiency, energy and atmosphere, building materials and waste reduction. It is the standard in the United States and some other countries for building sustainability.

The energy-efficiency project began in the 1990s and was initiated by C.M. Capital Corporation, an investment company that owns the building.

Large-scale efficiency conversions included lighting retrofits, elevator modernization and new chillers and boilers.

Tenants have saved more than $1 million in operating costs for utilities overall. Building-waste reductions and increased recycling have reduced trash-compactor pickups from three to one time a week and cut removal costs by 66 percent, Boreta said.

The City of Palo Alto Utilities (CPAU) offered technical assistance and provided $70,000 in project funding through rebates from its energy-efficiency programs.

Changes to the building operation will result in at least 1.6 million kilowatt hours of energy savings annually, with a utility bill reduction of at least $180,000 each year, according to Kinnear.

"This customer's great effort sets the example for others. We hope to partner with more businesses in Palo Alto to add more LEED certification to existing buildings," she said.

Palo Alto Office Center has also earned Energy Star certification for the past two years. Buildings with this rating must have a score of at least 75 points out of 100. Palo Alto Office Center's current score is 93, Boreta said.