The front door of Joan and Victor Johnson's Center City penthouse is no ordinary portal.

This circa-1810 paneled-wood masterpiece, sturdy, beautiful, and evocative of the past, was seized like pirate's booty from a dealer at the Philadelphia Antiques Show several years ago - just after they had purchased another door.

"The timing wasn't great," says Joan, "but the find was."

A legendary collector and volunteer for the show that begins Friday night with a preview party at the Pennsylvania Convention Center, Joan knew that its rugged charm would set the stage for what they were creating beyond the threshold: a farmhouse in the heart of the city.

In 2008, after years of searching for an urban space to relieve them from maintaining their expansive Meadowbrook house and grounds, the Johnsons discovered a raw penthouse space in Center City that had the kind of character and grace they had grown to love in the suburbs. It even met Victor's ironclad requirement - "nonnegotiable," he insists - that there be on-site parking.

Then, the couple made an unusual decision: They would replicate, detail by detail, the farmhouse they had loved and were reluctantly leaving.

With painstaking care, the Johnsons re-created the handsome moldings, the room configurations, and the rural, rugged country look artfully mixed with magnificent rugs, collections of Pennsylvania German redware, weather vanes, stoneware jugs, and folk art that had surrounded them for decades.

"It was such a gift to know that our new space was totally familiar and that everything we loved would come with us," Joan explains. "Change is hard, but this one really wasn't."

Case in point: The pine apple-peeling table that has served as the Johnsons' dining room table is again the room's superstar, with comfortable seating for 10.

The Johnsons, who married in November 1955, have been collecting antiques since those early married years, when they tackled the restoration of an old farm they had bought in Huntingdon Valley.

Joan, who had majored in art history at Goucher College in Baltimore, and also in Oslo, Norway, had always assumed she'd be a modernist when it came to design.

But Victor had grown up in an antique-filled home, and although he became a pioneer in adapting large banks and other businesses to computer technology, he didn't like the idea of coming home to a hard-edged look and feel.

In those early years, there was also the question of budget. "We filled that old farmhouse with things we could afford," says Joan, "and back then, older things were the perfect solution."

Victor, who quickly recognized his wife's keen eye, was delighted to see the first 1937 farmhouse transformed into a bucolic haven.

"Joan has always had this gift for design, but I still retained veto power," explains Victor. "I just almost never used it."

When a housing development cropped up and changed the landscape, the couple sold the farm and found another property in Meadowbrook designed as a classic farmhouse. This time, they got the look and feel without all the sweat equity.

The search for very special American art and antiques continued, strongly favoring Pennsylvania German. The New England countryside also provided a fertile area for finds.

That second farmhouse was the family anchor, starting from the years when their two daughters were at home. It was filled with things they loved, and its charms so captivated others that Joan was persuaded to launch her own interior design business, Joan Johnson Interiors, which she still operates from home. Clients often tap her encyclopedic knowledge of American antiques and art.

At the annual Philadelphia Antiques Show, it was Joan who served as the first loan exhibit chair, a volunteer position she then held for 38 years, through 2012, gathering antiques from various institutions. This year, the show's loan exhibit is Historic Deerfield, a display of the decorative arts of the Connecticut River Valley.

The couple's home, too, is host to many collections, including the historic weather vanes that once were scattered around the farmhouse, now clustered in the kitchen to dramatic and charming effect.

The couple also have an extensive collection of frakturs, American German folk art that is depicted on blessings, bookplates, and baptismal and marriage records.

It's these folksy touches that make this two-story space more farmhouse than penthouse.

While the living room is the most formal area, with decorative antique tables, side chairs, a daybed from 1720, a bride's chest, and a Chippendale-style sofa, the homespun feel is there, too, especially through the rugs that anchor the space.

Rooms are layered with a lifetime of objects that build harmony even as they showcase collections. Quilts dress upstairs beds, craft pieces are in nooks and crannies.

"For us," said Victor, "it's just the place where we can look around and see things that make us feel good. In other words, it's home."