To date, most LEED certifications in the U.S. have covered new buildings. By the end of 2009, about 46% of cumulative LEED certifications were under the LEED for New Construction (NC) program, with an additional 15% under the Core and Shell (CS) program. CS program certifies the “guts” of a new building project if the builder doesn’t have control complete control over the interior spaces.

In contrast, only about 31% of LEED certified space is under the Existing Buildings Operations & Maintenance (EB) program. (An additional 6% is under the LEED for Commercial Interiors (CI) program, which certifies spaces within new and existing buildings, as well as another 2% under specific LEED applications for schools, retail, and certain other types of buildings).

However, the tides have shifted in the last 18 months toward the existing building stock. In 2009, LEED EB surpassed LEED NC in terms of certified floor area by 15% in the U.S. How can we explain this shift?

One reason is that the last few years have witnessed a trend toward consolidation of building service companies. Many of the largest building service providers in the United States—including CB Richard Ellis, Jones Lang LaSalle, and Hines Corporation—are also the leaders in providing green building services. As a result, the early efforts of these companies to establish themselves as leaders in the green building sector are being amplified through their recent acquisitions as well as their prior service base.

The recession has also driven interest in existing buildings. Just as the recession all but halted new construction, it also drove many building managers to look at ways to reduce operating expenses in their existing building stock. Financing options such as energy performance contracts have helped capital-constrained building managers finance energy efficiency projects for existing buildings even through the recession, and LEED EB certification has accompanied many of these projects.

The recession has also placed pressure on certifying buildings in the slow but competitive rentals market. LEED certification can help differentiate a building from non-certified buildings and, for the few commercial tenants looking to relocate or rent for the first time, a LEED certification is highly attractive.

There is tremendous untapped opportunity for certifying the existing building stock. The momentum that LEED EB has gained even in the recession will only grow stronger as the building industry picks up as whole.