Richard Miller recalls meeting the neighbors for the first time after moving into a Federal-style townhouse in the embassy-lined neighborhood of Kalorama. "My wife, Ellen, and I were standing outside on the stoop, and the garage door opened next door and a Rolls Royce came out, and inside was a second Rolls Royce. Across the street, the garage opened, and a fancy Mercedes came out. We thought, My god, who lives here? This was 1975, before prices were so out of control," says the retired educator and psychologist.

Exemplary members of the nonprofit world and practitioners of the afterhours mantra "family, food, and friends," the couple took a giant leap of faith that year, moving from a tiny, 11-foot-wide Georgetown two-bedroom townhouse into a 3,500-square-foot, four-bedroom Federal-style townhouse with a study and a sunroom.

"It was in bad repair," recalls Ellen, a high-profile lobbyist who in 2006 founded the Sunlight Foundation, a watchdog group that harnesses the power of the Internet to monitor and disseminate information about government spending. "We had plasterers in the house for six weeks just putting plaster on the walls." An architect friend was kinder: He told Richard that trying to warm up this formal home would be a lifelong project—but, in the end, a rewarding one. "You will be wrestling with this house your whole life to make it yours," said the friend. "But it's solid, it's substantial, and it's all you'll ever need."

Fast-forward to 2012, and the home, having sheltered Richard, Ellen, and daughters Annie and Elizabeth—not to mention guests from all over the globe and, most recently, frequent visits from grandchildren Eli, three, and Abigail, one—has indeed undergone a startling transformation. The most recent redevelopments: the kitchen, the sun porch, and the library. This new heart of the home was envisioned by Vincent Sagart of Poliform and Sagartstudio, and built by contractor Richard Kroos of Kroos Construction, who replaced the space's homey Southwestern décor with a modern look. Stone tiles, Spessart oak cabinetry, wooden stools, Silestone quartz counters, Nakashima chairs, and Kreon light fixtures come together to create a style that Sagart describes as "streamlined, peaceful, and organized." "This was not about redesigning someone's lifestyle," he says, "but about expanding, observing, adjusting to them."

"We loved our old kitchen. It was beautiful and functioned perfectly—but fingerprints wouldn't come off the redwood cabinets, and there were chips in the floor tile," says Ellen. Inspired by the family's George Nakashima dining table, Sagart suggested an Asian minimalist look to bring the home up to the present and into the future. The new space, in Ellen's words, is "all about the appliances." Their Wolf cooktop combination has a top-of-the-line wok burner for the couple's frequent forays into Chinese cooking, an induction burner ("It gets the kids' pasta cooking immediately," says Richard), and an indoor grill for steaks. "I'm obsessed with our dishwasher [by Miele]," says Ellen. "The faucet [Tara Profi by Dornbracht] is a big statement piece and works brilliantly for cleaning out the sink." And a visitor would never guess from the super-sleek appearance of the kitchen that it also houses a washer and dryer.

"We wanted the home, especially the kitchen, to work for both kids and adults," says Richard. "We needed to have a counter with stools and a stove and a table, but also plenty of room for kids to roll around on the floor." The sunroom, formerly a TV room and a playroom for their children, now serves as an adult reading area—though it is still a playroom for the couple's grandchildren.

One quirky feature of the home was a wine cellar, reachable through a floor plank in the kitchen. Sealing this entrance and replacing it with integrated Sub-Zero wine storage allows more space for counters and chairs, and room for the grandkids to play—even if it also poses a slight inconvenience. "It is now only accessible by going through the basement," Richard says.