Architects are calling the third version of the popular green-building rating system, Leadership in Energy and Environmental Design, a signif­icant improvement over earlier releases.

LEED 2009, which covers new construction, schools, core and shell, commercial interiors and existing buildings, “is a step forward,” says Greg Mella, a principal of SmithGroup, Washington, D.C., and a member of the American Institute of Architects committee on the environment.

Under LEED 2009, rolled out late last month by the U.S. Green Building Council, credits are standardized on a 100-point scale. Credits also have been reweighted.

Mella deems that important because it recognizes the connection between energy conservation and climate change. For example, for new construction, LEED 2.2 offered 25% of its points in the “energy and atmosphere” category; LEED 3.0 offers 31%. Weightings for sustainable sites and water efficiency also increased, whereas weightings for materials and resources and indoor environmental quality are de-emphasized, says the architect. The revised weighting is consistent with AIA’s position on sustainability, tasking architects to move toward designing carbon-neutral buildings by 2030.

Prior to LEED 2009, the rating system was identical for all projects throughout the U.S. With LEED 2009, for instance, a project in Arizona can earn bonus points if it addresses water efficiency,which is appropriate considering the shortage of water in the region, says Mella. A project in Washington, D.C., can earn more points if it addresses stormwater management, which is appropriate considering the impact of the district’s combined sewer overflow on Potomac River water quality, says Mella.

George D. Halkias, a principal in the Pittsburgh office of architect L. Robert Kimball & Associates, also lauds the changes to LEED, but he thinks regional credits need even more focus. For example, Pittsburgh and Philadelphia are treated the same when they shouldn’t be, he says. “It’s a huge change, but I don’t think it is quite done yet,” he adds.

Prerequisite

LEED 2009 has added a prerequisite: All LEED projects must reduce indoor potable water use by at least 20%. LEED’s prerequisites ensure that every LEED-certified project addresses fundamental sustainable design issues, such as energy efficiency, water conservation and fundamental building commissioning. LEED’s prerequisites distinguish this rating system from other systems that have no prerequisites, says Mella.

The new LEED has updated its references to the American Society of Heating, Refrigerating and Air-Conditioning Engineers’ standards, referencing 2007 standards in place of 2004 standards. “As standards like ASHRAE 90.1 raise the bar on performance, LEED’s adoption of more recent standards also raises the bar,” says Mella.

Calling the LEED 2009 changes “significant,” Mella maintains the rating system’s materials-and-resources section still needs work. LEED 2009 continues to use single-attribute criteria for recognizing sustainable building products and materials. AIA wants green-building rating systems to use life-cycle assessment data as the basis for decision-making.