Linda Mack: If you favored preservation before ...

"The greenest building is the one already built."

With that catchy slogan, historic preservation has staked out its place in today's most dynamic design movement -- the search for sustainability.

Behind this initiative is Richard Moe, a Minnesota native and president of the National Trust for Historic Preservation, a nonprofit advocacy group. Moe has announced his retirement after 17 years of heading the trust. He was in Minneapolis this week speaking to architects and preservationists on the topic "Old is the New Green."

About 10 years ago, the Green Building Council came up with a ratings system that rewarded such environmentally sound features as using local materials, energy-efficient windows and alternative-energy sources such as solar or geothermal. Called LEED, for Leadership in Energy and Environmental Design, this system has changed the way new buildings are designed. Like Olympic athletes competing for gold medals, architects strive to design projects that will achieve LEED status.

The TCF Bank Stadium at the University of Minnesota, for instance, earned LEED Silver; it used recycled steel, reduced storm water runoff and recycled construction waste. Macalester College's recently opened Markim Hall won LEED Platinum, the highest status, for its native landscaping and aggressive energy efficiency. Even the new Walser Subaru dealership in Burnsville trumpets its LEED certification.

But there was one problem with the original LEED system: It only addressed the design of new buildings.

Enter Moe, who from his office in Washington, D.C., looked across the street at the headquarters of the U.S. Green Building Council and saw a chance for a powerful partnership.

Since then he has been on the hustings preaching the importance of preservation in reducing our carbon footprint. Among the points he emphasizes are these:

•Existing buildings embody the energy it took to manufacture and transport the materials used to build them. Demolishing buildings means that energy is lost.

•While the design of new buildings is important, they represent a tiny fraction of our building stock. More than two-thirds of our buildings were built between 1946 and 1989, when building performance was ignored.

•On the other hand, pre-World War II buildings tend to be made of durable materials and use natural ventilation. For instance, the Eastern Market in Washington, D.C., was naturally air-conditioned when it was built in 1873: Air entered basement windows, then moved over the ice that kept the produce cold, up through main floor and out through high windows and a roof vent. In the 1970s, the windows and the vent were closed in a typical "modernization."

•Studies have found that old-fashioned wood windows are more sustainable than new-fangled aluminum ones, which must be replaced rather than repaired when they wear out.

•Old-fashioned walkable communities are more sustainable than sprawling new ones that require firing up an engine to run a small errand.

LEED has revised its guidelines to recognize the value of reusing existing buildings. To foster further compelling research, the trust has opened a Preservation Green Lab in Seattle to develop pilot projects that show how retrofitting buildings can save energy. Online resources such as the Preservation Nation website offer weatherization tips for owners of older homes and discussions about how to update houses without destroying important features.

Moe deserves credit for many superb initiatives at the National Trust: stopping the plans to build a theme park near Virginia's Civil War battlefields; opening a field office in New Orleans after Hurricane Katrina to prevent the demolition of thousands of reusable houses; jump-starting a movement to preserve modern architecture by buying Mies van der Rohe's Farnsworth House; restoring the Lincoln Cottage in Washington, D.C., and helping to build local and state groups such as the Preservation Alliance of Minnesota.

None is likely to be as far-reaching as infusing the environmental movement with the value of preserving what we have already built. It will be a lasting legacy.

Linda Mack is a former architecture columnist for the Star Tribune.