PLYMOUTH – Old homes and historic buildings in the state are also the original "green" buildings, close to 200 community leaders learned yesterday.

Taking advantage of natural sunlight, thick walls, high ceilings and shade to cool in the summer, these structures are more energy efficient than structures built in the mid 1900s.

The only buildings more energy efficient than buildings built before 1920s are those built after 2000, Emily Wadhams, vice president for public policy with the National Trust for Historic Preservation told those attending the New Hampshire Preservation Alliance's spring conference held here yesterday at Plymouth State University.

Keeping those structures in New Hampshire rather than seeing them torn down is a goal of the Alliance, whose work includes developing leadership and technical assistance for communities to conserve history.

On a community scale, investment in older structures can reduce demands for new roads, utilities and other services that add to energy consumption, Wadhams said.

House sites took advantage of protection from wind and weather and orientation to the sun to capture natural factors. Enhancing these with modern-day energy efficiencies can be done, she noted.

Wadhams urged that investment in older buildings in communities needs to be a major component of sustainable living and historic preservation adds to a community's character and its attraction to visitors.

The Alliance chose Plymouth for this year's spring conference to highlight things that are being done in the community and at Plymouth State University to further those goals.

The conference, which continues today, includes a tour of the town's historic Boston & Maine railroad station, which has been renovated into a senior center, and a tour of the university's Mary Lyon Hall, which was recently renovated to combine energy efficiency and historic preservation.

Plymouth State University is also, for the first time, offering a four-course graduate certificate in historic preservation that can be pursued alone or as part of a master of education in heritage studies degree.

W. Rhett Lamb of the Keene Planning Commission made a number of observations for local preservationists as part of the conference yesterday.

He said the key to preservation is to develop a list of what you have, be deliberate and patient, make sure to tell the story and put time and energy into public outreach.

Lamb said he has successfully used pictures from the mid-1800s to show what was there.

"A lot of times we are dealing with incremental change," he said, urging patience.

Lamb recommended preservation groups submit an annual report at town meeting and be there annually to "keep it in front of them."

He urged leaders to identify and retain a core group of volunteers and keep them active doing research on inventory of what is there to help build the case for preservation.