“Going green can be costly, and there’s a lot to learn,” said Katie Ginsberg, who owns a four-bedroom 1960s Colonial in Chappaqua, N.Y., ”so we decided to start small and go from there.”

Defining “small” as a 600-square-foot home office built over the garage, Ginsberg and her husband, Peter, included a number of environmentally friendly elements in the addition: walls heavily insulated with fiberglass and spray foam; surfaces coated with paints that do not emit volatile organic compounds; countertops of concrete and recycled glass; and floors of bamboo, a rapidly renewable product, instead of wood.

Ginsberg estimated the costs at 10 to 15 percent higher. Adding foam, for example, is costlier than using fiberglass alone, and the recycled glass and stone mixture for the countertops was pricier than granite.

But though the ultimate energy savings leave them satisfied with the end result, the Ginsbergs are among many homeowners to learn firsthand what the challenge of going green can represent. As Stephen Tilly, a Dobbs Ferry, N.Y., architect who designs green renovations, put it, “There’s a lot of misinformation out there about green.”

Some of that misinformation can be traced to what Adiel Gavish, the program director for the nonprofit Federated Conservationists of Westchester County, calls greenwashing: the misrepresentation of products or actions as green, when they really are not. “That’s the downside of green becoming such a hot topic,” Gavish said.

Filtering out the buzz to find the most suitable approach is often the hardest part for homeowners, she added.

Some, like Richard and Maryann Ellenbogen, of Pelham, N.Y., have taken an all-or-nothing approach. On a sunny day at their new Mediterranean-style home, the electricity meter runs backward, thanks to a bank of solar panels. Three geothermal wells help cool the house in summer and heat it in winter. And a water-reclamation system recycles rain and water from the heating and cooling systems for use on the lawn.

At 8,900 square feet, the house far exceeds the size standards set by the U.S. Green Building Council, a nonprofit organization dedicated to sustainable building design and construction. But with thermostats in every room and “an ungodly amount of insulation” pumped into the walls, Ellenbogen said, the cost of heating “is a lot less than it is for many smaller nongreen homes around here.”

In explaining how easy the house was on the environment, he noted that it had been built mostly with steel and concrete; wood was used only for doors, windows and molding.

But to Tilly, the Dobbs Ferry architect, “the greenest thing is to take an existing building and recycle it.”

He is designing the renovation of a 110-year-old farmhouse in Katonah, N.Y., for Jeff Tannenbaum and his wife, Nisa Geller — whose purchase of the house kept the land from being subdivided.

In Tilly’s view, “it’s anathema to take reasonably good houses and tear them down and scavenge them for parts.” He is a committee chairman for the Association for Preservation Technology International, in Springfield, Ill., whose mission is to conserve historic structures and their settings.