As apprentices to architect Frank Lloyd Wright, Cornelia Brierly and Peter Berndtson learned how to design homes that were in harmony with nature.

Snow flurried often in April 1940 when the newlyweds arrived here to oversee construction of a West Mifflin home set on a knoll. With Wright's help, Brierly designed the first Usonian home in Pennsylvania for her aunts, Hulda and Louise Notz. Inspired by Wright's design of hexagonal chairs for a Wisconsin home, she used the six-sided shape to lay out the Lutz Lane house, even employing it in the concrete floors.

Usonian homes are characterized by flat roofs, a carport, radiant heat embedded in the floors, built-in furniture and lighting, and natural wood on the walls. Wood, stone and brick were the typical building materials.

The two architects began supervising construction of the West Mifflin house after the inexperienced contractor defaulted. They eventually pitched a sheepherder's tent on the 14-acre property. Inside were two cots and a Coleman burner. As Taliesin fellows, the couple had become accustomed to living in tents, a common practice at the group's winter retreat in Scottsdale, Ariz.

Brierly was pregnant with her first child. Eventually, Wright named her Anna, after his own mother. Berndtson, whose roots were Swedish, suggested Brunhilda and his wife offered Svenya. Wright's third wife, Olgivanna, objected, saying that Svenya meant pig in five languages. One evening at Taliesin in Wisconsin, Wright showed the infant around the room and christened her Anna. When Berndtson suggested Brita as a middle name, Wright insisted that was too much of a name for a baby.

Fallingwater had just been completed and during construction, local masons who worked on that house learned how to lay stone in the way it appears in a quarry.

"When we needed help, these dedicated young men drove down from the mountains every day to lay the stone work for my aunts," Brierly wrote in her 1999 memoir, "Tales of Taliesin."

The Notz House went through several owners, then sat empty for four years until Jeree and David Kiefer bought it in March 2006. The roof leaked and burgundy carpet had been glued to the concrete floors. Over the past seven years, Mrs. Kiefer, who is from Baldwin Borough, and her husband, who is from Plum, have devoted themselves to restoring interior and exterior cypress woodwork. The year 2008 brought the "summer of sanding" because, Mrs. Kiefer recalled, "We sanded the entire exterior of the house."

Inside, the couple removed a chartreuse Formica kitchen counter and plywood cabinetry. The original bulkheads remain but Mr. Kiefer built new cabinets and installed Paperstone counters. The couple upgraded a master and guest bathroom while maintaining the simplicity prevalent in Wright homes.

"I do all the sanding, the staining, the finishing," said Mrs. Kiefer.

"We did not really understand how hard it was going to be," she said, adding that the couple, who are avid cyclists, always take a break from projects in November to enjoy the holidays.

"We've done a lot of rewiring because we keep adding lights," Mr. Kiefer said.

The dining room table is made of solid cypress.

"You couldn't put your chairs underneath," Mr. Kiefer said. Using archival pictures of the home, he plans to re-create the hexagonal chairs that Berndtson created for the table.

The couple's cat, Molly, loves sleeping inside a built-in wooden vanity in the master bedroom; a friend created a custom-made cushion for her.

Internet shopping made the search for wood and furnishings somewhat easier.

"You literally have to buy stuff online," Mrs. Kiefer said, adding that that's how she found pull chains for lights.

Another commission

Later in their partnership, during the 1950s, Brierly and Berndtson designed a home for Saul and Edith Lipkind in Swisshelm Park. Set on slightly more than an acre of land and sited on the brow of a hill, the home's layout is fan-shaped and its major rooms face east.

On the eastern side is a curved red deck cantilevered over concrete piers. It affords a spectacular view of the woods and connects each room to the outdoors. The home's western side features a circular garden with an entrance trellis draped in trumpet vine and a round 12-foot-wide pool.

"We call it the cocktail pool," said Bob Moore, who grew up on Long Island, N.Y., and lives there with Scott Wise.

Concrete block walls that surround the garden provide privacy.

The pair learned the home was for sale through one of Mr. Wise's relatives, who lived nearby. After Mr. Wise wrote a letter to the Lipkind family, the two men toured the property in August 2006. Mr. Wise loved it, but Mr. Moore was less than enthralled because he encountered a bevy of bees.

To reassure Lipkind family members that the house would not be torn down or ruined by an incongruous addition, Mr. Wise wrote to them, saying, "We're just going to respect it, fix it up and live in it."

The Lipkinds' triangular Henredon Heritage table remains in the dining room. The living room's comfortable, built-in sofa faces a vertical, sunken fireplace where they have occasionally cooked stew, cornbread and chili. In front of the sofa stands the Lipkinds' elegant, rectangular coffee table streaked with pink, gray and white marble.

After Mrs. Lipkind died, the new homeowners also adopted her cat, Miss Candy, now 17. Four colorful portraits of the feline's face, done in pop art style, hang in the guest bedroom.

After they bought the home, Mr. Wise wrote a letter to every person in this region who owns a home designed by Brierly and Berndtson, creating a collegial fraternity where people swap stories and ask the question: "Did you ever run into this problem and what did you do about it?"

"The guy who restored all of the wood at Fallingwater spent a whole afternoon here. He looked at every scrap of wood in the house and gave us some advice," Mr. Wise said. "It's the most peaceful place I've ever been. You just sort of soften up and expand."

Besides the living room fireplace, there's a fireplace in the master bedroom. There are two bedrooms and two baths; built-in closets line the wall closest to the garden.

To renovate the guest bath, they chose a textured pearlescent tile for the shower but kept the original "toe tester," designed to let a bather check the water's temperature before stepping inside. A chrome Thermidor heats the room; a Pennsylvania black slate counter frames the white sink. The next projects are restoring the master bath, kitchen and outdoor pool.

Both men love the wooded setting.

"You can't tell you're in the city during the summer," Mr. Wise said. Large and small potted plants decorate the curved deck; a hand cast bell made by Paolo Soleri, a Taliesin fellow who died this past week, rings occasionally. The bell was a gift from Bob Moore's brother, Kevin Moore, a landscape architect who will help them reimagine the garden.

Through South Side architect Jerry Morosco, they met Cornelia Brierly when she was 93 and living at Taliesin West. She died at age 99 in August 2012.

"This circular pattern was Cornelia's idea," Mr. Moore said, recalling that she asked them, "Don't you just love sitting out on your deck in the morning?"

The men asked her to suggest rugs for the house and specific trees for the garden but she replied with questions: "What kind of trees do you like? What would you like to have on your floor?"

Her point, Mr. Moore said, was, "Don't make it a museum. It's not meant just to be looked at. She never said, 'You're living in one of my houses.' "