It was literally a project that could make or break the house.

"The entire weight of the home rested on a center support in the back wall," explained retired Westinghouse engineer Don Miller.

Unfortunately, that was also the wall that had to come out if Mr. Miller and his wife, Cordelia, were to expand their tiny kitchen in Irwin. Add in the fact that their stone house is more than 200 years old, and you have the recipe for a disaster.

The Millers have lived here for 30 years, raising two boys and constantly renovating. There was a lot to do. The house, which is listed on the National Register of Historic Places, was constructed by Col. John Irwin between 1792 and 1798.

"We always wanted an old house," said Mrs. Miller. "It had no character when we found it."

Much of the original character had been erased by a parade of previous owners trying to update the simple house. "Improvements" ranged from a new central staircase installed in 1870 to dropped ceilings added in the 1950s. But structural problems were mostly ignored.

"At one point, we had to dig up the cellar and jack up the whole first floor of the house, which was sagging," said Mr. Miller.

"He has done just about everything in this house himself," his wife added.

With the structure's integrity on the line, the family insisted he get some help.

"My family implored me to get an architect," recalled Mr. Miller, laughing.

He found architect John Timko of Timko and Associates in North Huntingdon. Together with master stone mason Lou Durka of Custom Concrete in Mount Pleasant, he managed to make a wide pass-through in the 2-foot-thick exterior wall. By the time Mr. Durka was finished creating stone arches in the style of a Roman aqueduct, there was enough original stone left over to cover the new back wall of the house. The addition extends 8 feet beyond the original outer wall.

A new bay window added another 2 1/2 feet and created a well-lit nook with room for the kitchen table and chairs.

To delineate the old space from the new, the Millers decided not to extend the wide-plank oak flooring from the 1800s. In the addition, they had installed a radiant-heated terra-cotta tile floor. There was no thought given to replicating the house's original kitchen.

"The property had no interior kitchen at all," Mr. Miller noted. "When it was built, they had three slaves and the kitchen was in a separate building."

The walls on the addition are finished in slightly wavy Colonial-style plaster. Green granite counter tops and custom cabinets hug the new back wall, and plenty of light floods the space from multiple windows. The kitchen has three sinks, two dishwashers and two garbage disposals. To mimic the stone arch, Mr. Miller built a cabinet of the same shape. A radiant-heated center island bridges the old and new spaces.

"I didn't think we'd ever use it, and I wasn't even sure I would like it. But now it's where we spend most of the time," noted Mrs. Miller.

Mr. Miller, who designed the kitchen, said, "Dilly can never make up her mind, so I just chose a design and did it."

Mrs. Miller admitted she had trouble visualizing the end result from the blueprints. Her husband, meanwhile, excels at finding new uses for old house pieces. He refitted an 1890s armoire they found at an antique store in Chautauqua, N.Y., where they spend their summers. It's now a pantry.

"It's a wonderful use of space," Mrs. Miller said.

Travel is another of their passions, and they are particularly fond of Italy. They used decorative ceramic tiles imported from Orvieto in the backsplash behind the Viking cooktop. The platter above the hood is also from Orvieto.

Restoring the house has been a monumental task.

"It's definitely addicting," Mr. Miller confessed.

And he's not finished.

"We are planning to enclose the second-floor porch next," he said, smiling.