When a friend from college got his doctorate in soil sciences, he asked to be called Dr. Dirt. Now that he’s been a professor of environmental sciences for years, we like to call him Dr. Sustainability, and the last time a bunch of us got together he was the go-to guy for all our questions.

“Hey, doctor, paper or plastic?”

“Doc, is it better to use the hot air dryer or the paper towel dispenser to dry your hands?”

“Hybrid or good gas mileage?”

“Hey, what about all these new LEED-certified buildings popping up on college campuses?”

The good doctor is not always predictable. He approves of LEED certification, of course, but wonders whether unnecessary — and unnecessarily large — buildings are being put up when existing buildings could be retrofitted and reused at less cost, and with less waste.

“When’s the last time you saw a college knock down a building?” the doctor asked, and because we’re an argumentative bunch, a few who also work at colleges gave examples of, say, old fieldhouses and office rows coming down for a gleaming new LEED building.

Still, the doctor’s point is interesting. LEED stands for Leadership in Energy and Environmental Design, and the official certification, which comes one year after the building is occupied, indicates that it was built with recycled or sustainable materials and that it operates in ways that conserve energy and water. That might include situating the building to take advantage of natural light, recycling waste water for utilities, using natural and renewable building materials and super-insulating walls to cut down on heating.

I guess the doctor worries that LEED buildings are a fad, and that unneeded buildings are going up so that a college can say it has one or so a business can look like a more responsible citizen of Earth. Some of the buildings are excessively large, and the stated energy-use savings are in comparison to mega-office complexes.

A better way to save energy, water and money might be to find creative ways to reuse existing buildings — adding insulation, enlarging windows, installing solar panels or changing the roof. Building recyclers could plant trees for summer cooling and install motion-detector lights that turn off automatically when the building is not in use; they could zone heating, and use thermostats to lower the temperature at night.

These are the kinds of changes we can make in our own homes. When your incandescent light bulb blows, replace it with a compact florescent bulb. Close your drapes or shades at night in the winter to keep heat in the house. Put up your storm windows, weatherstrip around doors. Turn off the water while brushing your teeth. Small changes, small improvements can add up to big savings, especially when you multiply it over the multitudes.

If a brand-new building is warranted, LEED guidelines seem like the way to go. Using sustainable materials and creating energy-efficient buildings powered by renewable sources clearly makes sense in the long run. But I wonder why so many closed supermarkets and drug store buildings stand vacant or are bulldozed as new ones go up. Isn’t there some way to reuse existing buildings? And does everything need to be so big?

High energy costs might be a reason the McMansion era is winding down, and new houses are getting smaller again. Still, Americans seem to need more space than people in other countries. Here, a 2,000-square-foot house is considered modest for a family of four. But the typical American lives in twice the square-footage than most Europeans, according to dozens of sources, including the Worldwatch Institute and the U.S Department of Energy.

Maybe, the doctor says, we should consider living just a little smaller.

As for our other questions, bringing your own shopping bag eliminates the need for either paper or plastic. The doctor drives a fuel-efficient small Honda, but lives close to work in a walkable/bikeable town.

And dryer or paper towel? The good doctor says he just wipes his hands on his pants. Lucky he’s no longer working in soil.

Margaret Hartley is the Gazette’s Sunday and projects editor. This column originally appeared in Sept. 28 on the Gazette’s Environment page.