CNN — (CNN) -- Some would knock on the door, like the unstable man who claimed he was Satan and had come to kill Jesus. Others burst in unannounced, carrying casserole dishes for the church potluck or looking for the spot where they'd been pronounced husband and wife.
The surprise visitors diminished slightly over the years as Alyn Carlson planted trees and built a stone wall around the converted New England church she and her family called home for more than 30 years. The landscaping made it look more like a house than a nondenominational church built in the early 20th century. But transforming a 4,000-square-foot sanctuary into a home has its obstacles.
"A church is made for a specific reason, so you can enter and leave the rest of the world behind," said Carlson, an artist and graphic designer in Westport, Massachusetts. "How can I make a wide-open space cozy and intimate? That was the challenge."
As the concept of adaptive use, or reusing an old structure for a new purpose, becomes more popular, property owners are breathing new life into religious buildings as homes, offices, community centers, bookstores, restaurants, even nightclubs.
"In terms of sustainability, both cultural and environmental, there's nothing better really than adapting an existing structure to a new use. It helps create a stronger community by stitching the history of the community together with a localized framework," said architect Bill Leddy, chairman of the American Institute of Architects Committee on the Environment.
Churches, especially Gothic and Baroque edifices in urban areas, are not the most common candidates for adaptive reuse. Depending on its size, an old church or cathedral can be costly to heat in the winter and keep cool in the summer. If it's old, it might take a lot of work and even more money to upgrade electric systems and plumbing.
But there's something about them -- maybe the vaulted ceilings or the large stained-glass windows and wood-paneled walls -- that ambitious rehabbers and hopeless romantics find hard to resist.
"Churches have a distinctive quality. Many of them are saved not just for the fact that they're sustainable but for the fact that they're unique and historic," said Leddy, founding partner of the Leddy Maytum Stacy Architects firm in California's San Francisco Bay Area.
Their historic value often protects them from being demolished or altered significantly, which can be a blessing and a curse for adaptive use, said architect Craig Rafferty, chairman of the architecture institute's Interfaith Forum on Religion, Art and Architecture. Elaborate facades and features like steeples, altars, religious carvings and large wooden doors might be visually stunning but impractical for secular purposes.
"You need to understand the architectural quality of the space and find activities that are compatible," he said. "If you want a small, intimate cottage, a 300-person church is not the best starting point."
Some congregations outgrow their homes or their needs evolve, especially for progressive congregations looking to turn their houses of worship into a kind of community center or third place for followers, Rafferty said.
Usually, congregations leave religious buildings for financial reasons, when declining membership makes sustaining a property unreasonable or maintenance and upkeep simply become too expensive, said religious scholar Dave McConeghy, who specializes in contemporary American religious history, spatial theory and sacred space.
But even if you take the congregation out of the church, traces of the past linger.
Pableaux Johnson wasn't looking for a new home when he came upon the old Methodist church in southern Louisiana while helping friends move into the home next door. But he was immediately drawn to its clean, simple lines and wondered why no one was using it.
"It was just beautiful. Nobody had used it in years, but it was made out of old grown cypress. Built like a truck," the freelance writer and photographer said. "If someone had bought the thing and torn it down, would've been worth more as scrap."
When he learned that the structure was in danger of being torn down, Johnson, who grew up in the area, saw a "preservation project." Plus, he'd have a place to stay when he came down to visit his father.
"We tried to muck with it as little as possible to be stewards of someone else's history," he said.
It took about two years to clean out and renovate the 1,400-square-foot space, during which he found a rafter with 1904, the year it was built, etched into the surface. With the help of friends, he built a loft for a master bedroom and bathroom. The altar became the kitchen, to honor the importance of communal cooking, food and drink in Southern culture. Out of the pews, he created chairs for a breakfast nook and a long dining table.
He held on to it for about a decade, until his father moved out of the state and he decided to sell it. It was important that he "keep it in the family," so he sold it to a friend who was also from the area.
Historian Rien Fertel was in the middle of his Ph.D. dissertation on Louisiana history at Tulane when he came by to check out the place.
"Here was this little church in the middle of the the original French Louisiana settlements," said Fertel, who grew up in Lafayette. "It just felt right."
Fertel, a history teacher at Tulane, divides his time between New Orleans and the church home in St. Martinsville. When he's not there, he opens it to friends who are writers and musicians looking for a creative retreat, allowing him to honor its history as a gathering place open to the community.
When he is there, he almost forgets that he's in a church until he wakes up to the colored light streaming through the stained glass. That, and when strangers come a-knocking, curious to hear about its history. In those moments, Fertel becomes aware of what it means to own a piece of local history.
"It feels very delicate. Especially with it being a church, you get the sense of everything that has happened here, how many people have used it, the funerals, weddings, the services," he said. "You feel very responsible for everything: the walls, the roof and just every little detail because it's so dang old."
Carlson likens the responsibility of tending to her New England church to caring for an "elderly relative."
"You're always taking care of stuff just to keep it alive and protect it from nature," she said. "It is a building like most old buildings, and it's never going to be finished."
Carlson and her husband, a minister, moved into the attached Sunday school in 1981 after their congregation bought the property. When the congregation decided to sell the property in 1986, the couple assumed the mortgage, paying $60,000 for the 4,000-square-foot structure and three acres of property.
It took several years to transform the sanctuary into two lofts connected by a catwalk. The choir loft became a master bedroom with a bathroom nestled in the steeple. They brought the attached Sunday school down to its foundation and built a combined office and living space for their three children. Then, they began the monumental task of transforming the parking lot into a backyard with a fire pit, garden and swings.
After her three children moved out, she and her husband opened their home to the community. They hosted parties, plays, operas, weddings, even a firewalk in the backyard. But, they never figured out the perfect solution for keeping the place warm on cold winter nights. And cleaning never gets easier when everything is big, from the floors and walls to kitchen table and bookshelves.
Like Johnson, Carlson eventually decided it was time to move on. The time came a few years after she and her husband divorced and she bought him out. She had given as much as she was willing to give to the church and wanted to focus more on her art.
At 2,000 square feet, her new home, a rental near a dairy barn, is still sizable. But, she can tell the difference in the amount of time it takes to clean.
She feels good about the young couple who took over the place. They remind Carlson of her and her ex-husband, "good, strong backs and lots of ideas." They kept her chickens and plan to execute on an idea for a patio that she never got around to.
"They're continuing the work of keeping the place alive," she said. "But they have their own ideas, and I trust them."
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